Patent Application
20080121903
The present invention contains subject matter related to Japanese Patent Application JP 2006-316885 filed in the Japanese Patent Office on Nov. 24, 2006, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a method for manufacturing a light-emitting diode, a light-emitting diode, a light source cell unit, a light-emitting diode backlight, a light-emitting diode illuminating device, a light-emitting diode display, and an electronic apparatus, and more particularly, relates to a light-emitting diode using a nitride-based III-V compound semiconductor and to various devices and/or apparatuses using this light-emitting diode.
2. Description of the Related Art
When a GaN-based semiconductor is epitaxial-grown on a different type substrate such as a sapphire substrate, since the differences in lattice constant and coefficient of thermal expansion therebetween are large, crystal defects, in particular threading dislocations, occur at a high density.
In order to avoid this problem, heretofore, a technique to decrease the dislocation density by a selective lateral-direction growth has been widely used. In this technique, after a GaN-based semiconductor is epitaxially grown on a sapphire substrate or the like, the substrate is recovered from a crystal growth apparatus, a growth mask is then formed on the GaN-based semiconductor layer using a SiO2 film or the like, this substrate is then again placed in the crystal growth apparatus, and subsequently, a GaN-based semiconductor layer is again epitaxially grown using this growth mask.
According to this technique, the dislocation density of the upper-side GaN-based semiconductor layer can be decreased; however, since epitaxial growth is performed twice in this case, the manufacturing cost is unfavorably increased.
Accordingly, a method has been proposed in which after an irregularity-forming process is performed beforehand on a different type substrate, a GaN-based semiconductor is epitaxially grown on this processed substrate (for example, see “Development of high-output UV LED using a LEPS method” Mitsubishi Cable Industries Review, No. 98, October 2001, and Japanese Unexamined Patent Application Publications Nos. 2004-6931 and 2004-6937). This method is schematically shown in
As shown in
In
In
Growth methods have also been proposed in which convex portions are formed on a substrate using a material different therefrom, and the growth of a nitride-based III-V compound semiconductor is started from concave portions between the convex portions (for example, see Japanese Unexamined Patent Application Publication No. 2003-324069 and Japanese Patent No. 2830814); however, the above growth manner is apparently different from that of the present invention.
According to the related method shown in
On the other hand, by the related growth method shown in
Furthermore, in both related growth methods shown in
Accordingly, it is desirable to provide a light-emitting diode and a manufacturing method thereof, the light-emitting diode having a significantly high luminous efficiency due to significant improvement in light extraction efficiency and improvement in internal quantum efficiency by significant improvement in crystallinities of nitride-based III-V compound semiconductor layers forming a light-emitting diode, being manufactured at a reasonable cost by one epitaxial growth, and using a substrate which can be easily processed by an irregularity-forming process.
In addition, it is also desirable to provide a high-performance light source cell unit, light-emitting diode backlight, light-emitting diode illuminating device, light-emitting diode display, and electronic apparatus, each using the light-emitting diode as described above.
The light-emitting diode, the manufacturing method thereof, and the various electronic devices and apparatuses using the above light-emitting diode described above will become apparent from the following description with reference to the accompanying drawings.
In order to solve the problems described above, the inventors of the present invention carried out intensive research, and the results obtained therefrom are as described below.
According to the knowledge of the inventors of the present invention, in the case in which nitride-based III-V compound semiconductor layers forming a light-emitting diode structure are grown, when a substrate provided with convex portions on one major surface, which are formed of a different material from the substrate, that is, a concavo-convex substrate, is used, a first nitride-based III-V compound semiconductor layer is first grown in a concave portion on the substrate through the state of a triangle cross-sectional shape using the bottom surface of the concave portion as the base, and a second nitride-based III-V compound semiconductor layer is then grown on the substrate from the first nitride-based III-V compound semiconductor layer in a lateral direction, spaces can be prevented from being formed among the substrate, the first nitride-based III-V compound semiconductor layer, and the second nitride-based III-V compound semiconductor layer. In addition, since the crystallinity of the second nitride-based III-V compound semiconductor layer can be made superior, the crystallinities of a third nitride-based III-V compound semiconductor layer, an active layer, and a fourth nitride-based III-V compound semiconductor layer, which are sequentially grown on the second nitride-based III-V compound semiconductor layer, can also be significantly improved.
In addition, through intensive research carried out by the inventors of the present invention, it was found that when the substrate as described above is used, by appropriately selecting a material for the convex portions, the far-field pattern (intensity distribution at a far-field point) of a light-emitting diode can be controlled without using an optical component such as a lens. In this case, appropriate selection of a material for the convex portions means that the ratio between the radiant flux from the upper surface and that from the side surface of a light-emitting diode is changed, and the far-field pattern can be controlled while the decrease in luminous efficiency is suppressed which is caused by attenuation of light emitted from the active layer due to the total reflection thereof in semiconductor layers forming the light-emitting diode structure. Light-emitting diodes are used in various application fields, such as displays, backlights, and illuminating devices, and since desired light emission intensity distribution varies depending on applications, it is very significant to be able to control the far-field pattern as described above. Hereinafter, the particular findings obtained by the inventors of the present invention will be schematically described.
The luminous efficiency of the light-emitting diode is determined by the internal quantum efficiency and the light extraction efficiency. The light extraction efficiency indicates the ratio of light beams escaping outside the light-emitting diode to light beams emitted from the active layer thereof, and improvement in light extraction efficiency is particularly important to improve the brightness of the light-emitting diode. In general, since light beams emitted from the active layer are difficult to escape out of the semiconductor layers forming the light-emitting diode due to the total reflection, while traveling to and from in the semiconductor layers, the light beams are attenuated. Inside the semiconductor layers, although light beams in an escape cone can escape outside, many light beams which are not in the escape cone are attenuated, and as a result, the light extraction efficiency is decreased.
In the light-emitting diode in which the nitride-based III-V compound semiconductor layer forming a light-emitting diode structure is grown using the above concavo-convex substrate, by its concavo-convex structure, the attenuation caused by the total refection inside the nitride-based III-V compound semiconductor layer can be suppressed, and the number of light beams entering the escape cone can be increased. That is, when the cross-sectional shape of the nitride-based III-V compound semiconductor layer forming a light-emitting diode is an ideal rectangular shape, light beams which do not enter the escape cone continue to be reflected at the interface between this nitride-based III-V compound semiconductor layer and the external medium, and as a result, the light beams are attenuated. However, on the other hand, as shown in
In general, the far-field pattern of light emitted from an upper surface of a light-emitting diode as shown in
In the light-emitting diode shown in
By a distance D from a luminous point to a reflection surface shown in
In the light-emitting diode having a concavo-convex structure as shown in
Also in a light-emitting diode shown in
The most preferable range of the refractive index of the convex portion 2 described above is effective regardless of the angle θ between the major surface of the substrate 1 and the side surface of the convex portion 2, the width Wt of the convex portion 2, the height d thereof, the width Wg of the concave portion 6, the plan shape of the convex portion 2, the two-dimensional arrangement pattern thereof, the light-emitting wavelength λ, and the like.
In addition, when a ferroelectric substance is selected as the medium of the convex portion 2, by applying an external electric field to the convex portion 2, the refractive index of the convex portion 2 can be changed by the electro-optical effect. In this case, as is the case described above, since the side-surface luminous ratio and the light extraction efficiency are changed, the far-field pattern can be continuously changed by electric field application.
The present invention has been conceived based on the findings described above by the inventors of the present invention.
That is, in order to solve the problems described above, according to a first embodiment of the present invention, there is provided a method for manufacturing a light-emitting diode, comprising the steps of: preparing a substrate provided with convex portions on one major surface, the convex portions being formed from a dielectric substance which is different from the substrate and which has a refractive index of 1.7 to 2.2; growing a first nitride-based III-V compound semiconductor layer in a concave portion on the substrate through the state of a triangle cross-sectional shape using the bottom surface of the concave portion as the base; growing a second nitride-based III-V compound semiconductor layer on the substrate from the first nitride-based III-V compound semiconductor layer in a lateral direction; and sequentially growing, on the second nitride-based III-V compound semiconductor layer, a first conductive type third nitride-based III-V compound semiconductor layer, an active layer, and a second conductive type fourth nitride-based III-V compound semiconductor layer.
The first nitride-based III-V compound semiconductor layer and the second nitride-based III-V compound semiconductor layer may have any conductive type, that is, any one of a p-type, an n-type, and an i-type, and may have or may have not the same conductive type. In addition, in the first nitride-based III-V compound semiconductor layer or the second nitride-based III-V compound semiconductor layer, at least two portions having different conductive types may be simultaneously present.
Typically, in the growth of the first nitride-based III-V compound semiconductor layer, when dislocation is generated from the interface with the bottom surface of the concave portion on the substrate in a direction perpendicular to one major surface thereof and then extends to the inclined surface of the first nitride-based III-V compound semiconductor layer in the state of the above triangle cross-sectional shape or to the vicinity of the inclined surface, the dislocation is bent in a direction parallel to the above major surface so as to be apart from the triangle shape portion. In this case, the triangle cross-sectional shape or the triangle of the triangle shape portion does not only indicate a precise triangle shape but also includes a shape approximately regarded as a triangle, such as a triangle having a round apex (hereinafter, the triangle indicates the same as described above). In addition, preferably, at the early growth stage of the first nitride-based III-V compound semiconductor layer, minute nuclei are generated from the bottom surface of the concave portion on the substrate, and during the process including the growth and coalescence of the minute nuclei, dislocations generated from the interfaces with the bottom surfaces of the concave portions on the substrate in a direction perpendicular to one major surface thereof are repeatedly bent in a direction parallel to the major surface described above. Accordingly, when the first nitride-based III-V compound semiconductor layer is grown, the number of dislocations propagated to the upper side can be decreased.
Typically, the convex portions and the concave portions are alternately and periodically formed on one major surface of the substrate. In this case, the interval of the convex portions and that of the concave portions are each preferably 3 to 6 μm; however, the interval is not limited thereto. In addition, the ratio of the length of the bottom surface of the convex portion to the length of the bottom surface of the concave portion is preferably in the range of 0.5 to 3 and most preferably approximately 0.5; however, the ratio is not limited thereto. The height of the convex portion from the major surface of the substrate is preferably 0.3 μm or more and more preferably 1 μm or more. This convex portion preferably has at least one inclined surface with respect to the major surface of the substrate, and when the angle between this side surface and the major surface of the substrate is represented by θ, in order to improve the light extraction efficiency, for example, 30°<θ<80° preferably holds, and θ is most preferably approximately 40°; however, the angle θ is not limited thereto. The convex portion may have various cross-sectional shapes, and the side surface thereof may also be a curved surface as well as a flat surface; for example, an n-polygon (in which n is an integer of 3 or more), such as a triangle, a quadrangle, a pentagon, or a hexagon; an n-polygon as mentioned above having at least one truncated or rounded apex; a circle; or an oval may be mentioned. Among those mentioned above, a shape having one apex at a highest position from the major surface of the substrate is preferable, and in particular, a triangle or a triangle having a truncated or rounded apex is most preferable. The cross-section of the concave portion may also have various shapes, and for example, an n-polygon (in which n is an integer of 3 or more), such as a triangle, a quadrangle, a pentagon, or a hexagon; an n-polygon as mentioned above having at least one truncated or rounded apex; a circle; or an oval may be mentioned. In order to improve the light extraction efficiency, the cross-section of this concave portion preferably has an inverted trapezoid. In this case, the inverted trapezoid does not only indicate a precise inverted trapezoid but also includes a shape approximately regarded as an inverted trapezoid (hereinafter, the inverted trapezoid indicates the same as described above). In this case, in order to minimize the dislocation density of the second nitride-based III-V compound semiconductor layer, when the depth of the concave portion (same as the height of the convex portion), the width of the bottom surface of the concave portion, and the angle between one major surface of the substrate and the inclined surface of the first nitride-based III-V compound semiconductor layer in the state of a triangle cross-sectional shape are represented by d, Wg, and α, respectively, d, Wg, and α are preferably determined so that 2 d≧Wg×tan α holds. Since the angle α is generally constant, d and Wg are determined to satisfy the above equation. When the depth d is excessively large, since a raw material gas is not sufficiently supplied inside the concave portion, the growth of the first nitride-based III-V compound semiconductor layer from the bottom surface of the concave portion may have a problem, and on the other hand, when the depth d is excessively small, in addition to the concave portion on the substrate, the first nitride-based III-V compound semiconductor layer is also grown on the convex portions located at the two sides of the above concave portion. In order to prevent the above problems, the depth d is generally determined in the range of 0.5 to 5 μm and is typically set to 1.0±0.2 μm; however, the depth d is not limited thereto. The width Wg is generally 0.5 to 5 μm and is generally set in the range of 2±0.5 μm; however, the width Wg is not limited thereto. In addition, the width of the upper surface of the convex portion is 0 when the cross-sectional shape thereof is a triangle; however, when the cross-sectional shape of the convex portion is a trapezoid, since this convex portion is a region to be used for the lateral growth of the second nitride-based III-V compound semiconductor layer, an area having a low dislocation density can be increased as the width of the upper surface of the convex portion is increased. When the cross-sectional shape of the convex portion is a trapezoid, the width Wt is generally 1 to 1,000 μm, such as in the range of 4±2 μm; however, the width Wt is not limited thereto.
The convex portions or the concave portions may be formed in a stripe pattern to extend in one direction on the substrate or may be formed in a stripe pattern to extend in a first direction and a second direction on the substrate to intersect each other. In the latter case, the convex portions may have a two-dimensional pattern including an n-polygon (in which n is an integer of 3 or more), such as a triangle, a quadrangle, a pentagon, or a hexagon; an n-polygon as mentioned above having at least one truncated or rounded apex; a circle; an oval; or a dot. As one preferable example, the convex portions each have a hexagonal planar shape and are two-dimensionally arranged to form a honeycomb pattern, and the concave portions are formed so as to surround the convex portions. Accordingly, light emitted from the active layer can be efficiency extracted in all the directions of 36020 . Alternatively, the concave portions each have a hexagonal planar shape and are two-dimensionally arranged to form a honeycomb pattern, and the convex portions may be formed to surround the concave portions. When the concave portions on the substrate have a stripe pattern, the concave portions may extend, for example, in the <1-100> direction of the first nitride-based III-V compound semiconductor layer or, when a sapphire substrate is used as the substrate, the concave portions may extend in the <11-20> direction of this sapphire substrate. The shape of the convex portion is, for example, an n-polygonal pyramid (in which n is an integer of 3 or more), such as a triangular pyramid, a quadrangular pyramid, a pentagonal pyramid, or a hexagonal pyramid; an n-polygonal pyramid as mentioned above having at least one truncated or rounded apex; an circular cone; or an oval cone.
As the dielectric substance forming the convex portions, any material which has a refractive index of 1.7 to 2.2 and which preferably does not remarkably absorb light having a light-emitting wavelength may be basically used, and for example, an oxide, a nitride, an oxynitride, or a fluoride may be mentioned. Whenever necessary, the convex portion may be formed by mixing at least two types of dielectric substances or by using a laminated film composed of at least two types of dielectric substances. The particular examples of this dielectric substance are shown below. However, besides the dielectric substances having the following stoichiometric compositions, dielectric substances having non-stoichiometric compositions slightly deviated therefrom may also be used.
In order to improve the light extraction efficiency of the light-emitting diode, the refractive index of the dielectric substance forming the convex portions is preferably in the range of 1.7 to 2.1 and most preferably approximately 2.0 (such as 1.9 to 2.1), and in order to improve the light-scattering property, the refractive index is most preferably approximately 2.0 (such as 1.9 to 2.1).
In order to grow the first nitride-based III-V compound semiconductor layer only in the convex portion on the substrate, for example, at least the surface of the convex portion is preferably formed of an amorphous layer. The reason for this is to use a phenomenon in which nuclear formation is not likely to occur on an amorphous layer during the growth.
In addition, since threading dislocations are concentrated at coalescent portions of the second nitride-based III-V compound semiconductor layers located above the convex portions, when dislocation-propagation inhibitory parts made of an insulating material, a void, or the like are formed beforehand on the convex portions so as to inhibit the propagation of dislocations in a direction parallel to one major surface of the substrate, the propagation of dislocations to the surface of the second nitride-based III-V compound semiconductor layer is inhibited, thereby preventing the formation of threading dislocations.
On the third nitride-based III-V compound semiconductor layer, a first conductive type electrode is formed so as to be electrically connected thereto. In a manner similar to that described above, on the fourth nitride-based III-V compound semiconductor layer, a second conductive type electrode is formed so as to be electrically connected thereto.
Various materials may be used for the substrate. As the substrate formed from a material different from the nitride-based III-V compound semiconductor, for example, in particular, there may be used a substrate formed from sapphire (c-plane, a-plane, r-plane, a plane offset from the aforementioned plane, or the like), SiC (6H, 4H, 3C, or the like), Si, ZnS, ZnO, LiMgO, GaAs, spinel (MgAl2O4, or ScAlMgO4), garnet, CrN (such as CrN(111)), or the like. A hexagonal substrate or a cubic substrate made of aforementioned materials is preferably used, and in particular, a hexagonal substrate is more preferably used. As the substrate, a substrate made of a nitride-based III-V compound semiconductor (GaN, AlGaInN, AlN, GaInN, or the like) may also be used. Alternatively, as the substrate, a nitride-based III-V compound semiconductor layer may be used which is grown on a base plate formed of a material different therefrom, and the convex portions may then be formed on this nitride-based III-V compound semiconductor layer.
In addition, for example, when a layer, such as a nitride-based III-V compound semiconductor layer, grown on a base plate is used as the substrate, as a material for the convex portions, a material different from that for a layer in direct contact therewith is used.
In the case described above, the substrate is not removed and is allowed to remain in a light-emitting diode which is finally manufactured as a product.
The first to the fourth nitride-based III-V compound semiconductor layers and the nitride-based III-V compound semiconductor layer forming the active layer are most commonly represented by AlxByGa1-x-y-zInzAsuN1-u-vPv (where 0≦x≦1, 0≦y≦1, 0≦z≦1, 0≦u≦1, 0≦v≦1, 0≦x+y+z<1, and 0≦u+v<1), in particular, represented by AlxByGa1-x-y-zInzN (where 0≦x≦1, 0≦y≦1, 0≦z≦1, and 0≦x+y+z<1), and typically, represented by AlxGa1-x-zInzN (where 0≦x≦1 and 0≦z≦1). As a concrete example, for example, GaN, InN, AlN, AlGaN, InGaN, or AlGaInN may be mentioned. Since an effect to facilitate the bending of dislocations is obtained, for example, when B, Cr, or the like is contained in GaN, the first to the fifth nitride-based III-V compound semiconductor layers and the nitride-based III-V compound semiconductor layer forming the active layer may be formed of BGaN, GaN:B obtained from GaN doped with B, GaN:Cr obtained from GaN doped with Cr, or the like. In particular, as the first nitride-based III-V compound semiconductor layer which is first formed in the convex portion on the substrate, GaN, InxGa1-xN (0<x<0.5), AlxGa1-xN (0<x<0.5), or AlxInyGa1-x-yN (0<x<0.5, 0<y<0.2) is preferably used. The first conductive type may be either an n-type or a p-type, and in accordance therewith, the second conductive type is a p-type or an n-type. In addition, as a so-called low-temperature buffer layer which is first formed on the substrate, a GaN buffer layer, an AlN buffer layer, an AlGaN buffer layer, or the like may be generally used, and in addition, a buffer layer formed by doping the aforementioned layer with Cr, a CrN buffer layer, or the like may also be used.
The thickness of the second nitride-based III-V compound semiconductor layer is appropriately determined and is typically approximately several micrometers or less; however, depending on applications or the like, the thickness may be larger than that described above, such as approximately several tens of micrometers to 300 μm.
As a method for growing the first to the fourth nitride-based III-V compound semiconductor layers and the nitride-based III-V compound semiconductor layer forming the active layer, for example, there may be used various epitaxial growth methods, such as metal organic chemical vapor deposition (MOCVD), hydride vapor phase epitaxial growth or halide vapor phase epitaxial growth (HVPE), and molecular beam epitaxial growth (MBE).
In accordance with a second embodiment of the present invention, there is provide a light-emitting diode comprising: a substrate provided with convex portions on one major surface, the convex portions being composed of a dielectric substance which is different from the substrate and which has a refractive index of 1.7 to 2.2; a fifth nitride-based III-V compound semiconductor layer grown on the substrate without forming a space in a concave portion on the substrate; and a first conductive type third nitride-based III-V compound semiconductor layer, an active layer, and a second conductive type fourth nitride-based III-V compound semiconductor layer, which are provided on the fifth nitride-based III-V compound semiconductor layer. In the light-emitting diode described above, in the fifth nitride-based III-V compound semiconductor layer, dislocation generated from the interface with the bottom surface of the concave portion in a direction perpendicular to said one major surface extends to an inclined surface of a triangle portion using the bottom surface of the concave portion as the base or to the vicinity of the inclined surface and is then bent in a direction parallel to said one major surface.
In the second embodiment and the following fourth to sixteenth embodiments of the present invention, the fifth nitride-based III-V compound semiconductor layer corresponds to the first and the second nitride-based III-V compound semiconductor layers according to the first embodiment of the present invention.
To the second and the following third to the sixteenth embodiments of the present invention, the description relating to the first embodiment of the present invention can also be applied, as long as materials to be used have common properties, that is, in other words, as long as particular materials or substances are not used.
In accordance with a third embodiment of the present invention, there is provide a method for manufacturing a light-emitting diode, comprising the steps of: preparing a substrate provided with convex portions on one major surface, the convex portions being formed from a dielectric substance which is different from the substrate and which has a refractive index of 1.0 to 2.3; growing a first nitride-based III-V compound semiconductor layer in a concave portion on the substrate through the state of a triangle cross-sectional shape using the bottom surface of the concave portion as the base; growing a second nitride-based III-V compound semiconductor layer on the substrate from the first nitride-based III-V compound semiconductor layer in a lateral direction; sequentially growing, on the second nitride-based III-V compound semiconductor layer, a first conductive type third nitride-based III-V compound semiconductor layer, an active layer, and a second conductive type fourth nitride-based III-V compound semiconductor layer; and removing the substrate.
In accordance with a fourth embodiment of the present invention, there is provided a light-emitting diode comprising: a fifth nitride-based III-V compound semiconductor layer; and a first conductive type third nitride-based III-V compound semiconductor layer, an active layer, and a second conductive type fourth nitride-based III-V compound semiconductor layer, which are provided on the fifth nitride-based III-V compound semiconductor layer. In the light-emitting diode described above, in one major surface of the fifth nitride-based III-V compound semiconductor layer located at a side opposite to that of the active layer, convex portions composed of a dielectric substance having a refractive index of 1.0 to 2.3 are buried, and in the fifth nitride-based III-V compound semiconductor layer, dislocation generated from between the convex portions in said one major surface in a direction perpendicular to said one major surface extends to an inclined surface of a triangle portion using a part between the convex portions as the base or to the vicinity of the inclined surface and is then bent in a direction parallel to said one major surface.
In this embodiment, the structure in which the convex portions composed of a dielectric substance having a refractive index of 1.0 to 2.3 are buried in one major surface of the fifth nitride-based III-V compound semiconductor layer located at a side opposite to the active layer is the same structure in the third embodiment of the present invention which is obtained by removing the substrate while the convex portions are allowed to remain.
In the third and the fourth embodiments of the present invention, as the dielectric substance forming the convex portions, any material may be basically used as long as it has a refractive index of 1.0 to 2.3 and preferably does not remarkably absorb light of a light-emitting wavelength, and in particular, besides the materials described in the first embodiment of the present invention by way of example, the following dielectric substances may also be mentioned. The convex portions may be formed by mixing at least two types of dielectric substances or may be formed from a laminated film containing at least two types of dielectric substances. However, besides the dielectric substances having the following stoichiometric compositions, dielectric substances having non-stoichiometric compositions slightly deviated therefrom may also be used. As the dielectric substance forming the convex portions, air (refractive index: approximately 1.0) may also be used.
In order to improve the light extraction efficiency of the light-emitting diode, the refractive index of the dielectric substance forming the convex portions is preferably in the range of 1.0 to 1.8 and is, in particular, more preferably approximately 1.55, and in order to improve the light-scattering property, the refractive index is preferably in the range of 1.3 to 1.85.
In accordance with a fifth embodiment of the present invention, there is provided a light source cell unit comprising: a plurality of arranged cells, each having at least one red light-emitting diode, at least one green light-emitting diode, and at least one blue light-emitting diode, in which at least one light-emitting diode of the red light-emitting diode, the green light-emitting diode, and the blue light-emitting diode includes, a substrate provided with convex portions on one major surface, the convex portions being composed of a dielectric substance which is different from the substrate and which has a refractive index of 1.7 to 2.2; a fifth nitride-based III-V compound semiconductor layer grown on the substrate without forming a space in a concave portion on the substrate; and a first conductive type third nitride-based III-V compound semiconductor layer, an active layer, and a second conductive type fourth nitride-based III-V compound semiconductor layer, which are provided on the fifth nitride-based III-V compound semiconductor layer. In addition, in the fifth nitride-based III-V compound semiconductor layer, dislocation generated from the interface with the bottom surface of the concave portion in a direction perpendicular to said one major surface extends to an inclined surface of a triangle portion using the bottom surface of the concave portion as the base or to the vicinity of the inclined surface and is then bent in a direction parallel to said one major surface.
In accordance with a sixth embodiment of the present invention, there is provided a light source cell unit comprising: a plurality of arranged cells, each having at least one red light-emitting diode, at least one green light-emitting diode, and at least one blue light-emitting diode, in which at least one light-emitting diode of the red light-emitting diode, the green light-emitting diode, and the blue light-emitting diode includes, a fifth nitride-based III-V compound semiconductor layer; and a first conductive type third nitride-based III-V compound semiconductor layer, an active layer, and a second conductive type fourth nitride-based III-V compound semiconductor layer, which are provided on the fifth nitride-based III-V compound semiconductor layer. In the light source cell unit described above, in one major surface of the fifth nitride-based III-V compound semiconductor layer located at a side opposite to that of the active layer, convex portions composed of a dielectric substance having a refractive index of 1.0 to 2.3 are buried, and in the fifth nitride-based III-V compound semiconductor layer, dislocation generated from between the convex portions in said one major surface in a direction perpendicular to said one major surface extends to an inclined surface of a triangle portion using a part between the convex portions as the base or to the vicinity of the inclined surface and is then bent in a direction parallel to said one major surface.
In accordance with a seventh embodiment of the present invention, there is provided a light-emitting diode backlight comprising: a plurality of red light-emitting diodes, a plurality of green light-emitting diodes, and a plurality of blue light-emitting diodes, the light-emitting diodes being arranged; wherein at least one light-emitting diode of the red light-emitting diodes, the green light-emitting diodes, and the blue light-emitting diodes includes, a substrate provided with convex portions on one major surface, the convex portions being composed of a dielectric substance which is different from the substrate and which has a refractive index of 1.7 to 2.2; a fifth nitride-based III-V compound semiconductor layer grown on the substrate without forming a space in a concave portion on the substrate; and a first conductive type third nitride-based III-V compound semiconductor layer, an active layer, and a second conductive type fourth nitride-based III-V compound semiconductor layer, which are provided on the fifth nitride-based III-V compound semiconductor layer; wherein in the fifth nitride-based III-V compound semiconductor layer, dislocation generated from the interface with the bottom surface of the concave portion in a direction perpendicular to said one major surface extends to an inclined surface of a triangle portion using the bottom surface of the concave portion as the base or to the vicinity of the inclined surface and is then bent in a direction parallel to said one major surface.
In accordance with an eighth embodiment of the present invention, there is provided a light-emitting diode backlight comprising: a plurality of red light-emitting diodes, a plurality of green light-emitting diodes, and a plurality of blue light-emitting diodes, the light-emitting diodes being arranged; wherein at least one light-emitting diode of the red light-emitting diodes, the green light-emitting diodes, and the blue light-emitting diodes includes, a fifth nitride-based III-V compound semiconductor layer; and a first conductive type third nitride-based III-V compound semiconductor layer, an active layer, and a second conductive type fourth nitride-based III-V compound semiconductor layer, which are provided on the fifth nitride-based III-V compound semiconductor layer; wherein in one major surface of the fifth nitride-based III-V compound semiconductor layer located at a side opposite to that of the active layer, convex portions composed of a dielectric substance having a refractive index of 1.0 to 2.3 are buried, and in the fifth nitride-based III-V compound semiconductor layer, dislocation generated from between the convex portions in said one major surface in a direction perpendicular to said one major surface extends to an inclined surface of a triangle portion using a part between the convex portions as the base or to the vicinity of the inclined surface and is then bent in a direction parallel to said one major surface.
In accordance with a ninth embodiment of the present invention, there is provided a light-emitting diode illuminating device comprising: a plurality of red light-emitting diodes, a plurality of green light-emitting diodes, and a plurality of blue light-emitting diodes, the light-emitting diodes being arranged; wherein at least one light-emitting diode of the red light-emitting diodes, the green light-emitting diodes, and the blue light-emitting diodes includes, a substrate provided with convex portions on one major surface, the convex portions being composed of a dielectric substance which is different from the substrate and which has a refractive index of 1.7 to 2.2; a fifth nitride-based III-V compound semiconductor layer grown on the substrate without forming a space in a concave portion on the substrate; and a first conductive type third nitride-based III-V compound semiconductor layer, an active layer, and a second conductive type fourth nitride-based III-V compound semiconductor layer, which are provided on the fifth nitride-based III-V compound semiconductor layer; wherein in the fifth nitride-based III-V compound semiconductor layer, dislocation generated from the interface with the bottom surface of the concave portion in a direction perpendicular to said one major surface extends to an inclined surface of a triangle portion using the bottom surface of the concave portion as the base or to the vicinity of the inclined surface and is then bent in a direction parallel to said one major surface.
In accordance with a tenth embodiment of the present invention, there is provided a light-emitting diode illuminating device comprising: a plurality of red light-emitting diodes, a plurality of green light-emitting diodes, and a plurality of blue light-emitting diodes, the light-emitting diodes being arranged; wherein at least one light-emitting diode of the red light-emitting diodes, the green light-emitting diodes, and the blue light-emitting diodes includes, a fifth nitride-based III-V compound semiconductor layer; and a first conductive type third nitride-based III-V compound semiconductor layer, an active layer, and a second conductive type fourth nitride-based III-V compound semiconductor layer, which are provided on the fifth nitride-based III-V compound semiconductor layer; wherein in one major surface of the fifth nitride-based III-V compound semiconductor layer located at a side opposite to that of the active layer, convex portions composed of a dielectric substance having a refractive index of 1.0 to 2.3 are buried, and in the fifth nitride-based III-V compound semiconductor layer, dislocation generated from between the convex portions in said one major surface in a direction perpendicular to said one major surface extends to an inclined surface of a triangle portion using a part between the convex portions as the base or to the vicinity of the inclined surface and is then bent in a direction parallel to said one major surface.
In accordance with an eleventh embodiment of the present invention, there is provided a light-emitting diode display comprising: a plurality of red light-emitting diodes, a plurality of green light-emitting diodes, and a plurality of blue light-emitting diodes, the light-emitting diodes being arranged; wherein at least one light-emitting diode of the red light-emitting diodes, the green light-emitting diodes, and the blue light-emitting diodes includes, a substrate provided with convex portions on one major surface, the convex portions being composed of a dielectric substance which is different from the substrate and which has a refractive index of 1.7 to 2.2; a fifth nitride-based III-V compound semiconductor layer grown on the substrate without forming a space in a concave portion on the substrate; and a first conductive type third nitride-based III-V compound semiconductor layer, an active layer, and a second conductive type fourth nitride-based III-V compound semiconductor layer, which are provided on the fifth nitride-based III-V compound semiconductor layer; wherein in the fifth nitride-based III-V compound semiconductor layer, dislocation generated from the interface with the bottom surface of the concave portion in a direction perpendicular to said one major surface extends to an inclined surface of a triangle portion using the bottom surface of the concave portion as the base or to the vicinity of the inclined surface and is then bent in a direction parallel to said one major surface.
In accordance with a twelfth embodiment of the present invention, there is provided a light-emitting diode display comprising: a plurality of red light-emitting diodes, a plurality of green light-emitting diodes, and a plurality of blue light-emitting diodes, the light-emitting diodes being arranged; wherein at least one light-emitting diode of the red light-emitting diodes, the green light-emitting diodes, and the blue light-emitting diodes includes, a fifth nitride-based III-V compound semiconductor layer; and a first conductive type third nitride-based III-V compound semiconductor layer, an active layer, and a second conductive type fourth nitride-based III-V compound semiconductor layer, which are provided on the fifth nitride-based III-V compound semiconductor layer; wherein in one major surface of the fifth nitride-based III-V compound semiconductor layer located at a side opposite to that of the active layer, convex portions composed of a dielectric substance having a refractive index of 1.0 to 2.3 are buried, and in the fifth nitride-based III-V compound semiconductor layer, dislocation generated from between the convex portions in said one major surface in a direction perpendicular to said one major surface extends to an inclined surface of a triangle portion using a part between the convex portions as the base or to the vicinity of the inclined surface and is then bent in a direction parallel to said one major surface.
According to the fifth to the twelfth embodiments of the present invention, as the red light-emitting diode, for example, a diode using an AlGaInP-based semiconductor may also be used.
In accordance with a thirteenth embodiment of the present invention, there is provided an electronic apparatus comprising: at least one light-emitting diode; wherein said at least one light-emitting diode includes, a substrate provided with convex portions on one major surface, the convex portions being composed of a dielectric substance which is different from the substrate and which has a refractive index of 1.7 to 2.2; a fifth nitride-based III-V compound semiconductor layer grown on the substrate without forming a space in a concave portion on the substrate; and a first conductive type third nitride-based III-V compound semiconductor layer, an active layer, and a second conductive type fourth nitride-based III-V compound semiconductor layer, which are provided on the fifth nitride-based III-V compound semiconductor layer; wherein in the fifth nitride-based III-V compound semiconductor layer, dislocation generated from the interface with the bottom surface of the concave portion in a direction perpendicular to said one major surface extends to an inclined surface of a triangle portion using the bottom surface of the concave portion as the base or to the vicinity of the inclined surface and is then bent in a direction parallel to said one major surface.
In accordance with a fourteenth embodiment of the present invention, there is provided an electronic apparatus comprising: at least one light-emitting diode; wherein said at least one light-emitting diode includes, a fifth nitride-based III-V compound semiconductor layer; and a first conductive type third nitride-based III-V compound semiconductor layer, an active layer, and a second conductive type fourth nitride-based III-V compound semiconductor layer, which are provided on the fifth nitride-based III-V compound semiconductor layer; wherein in one major surface of the fifth nitride-based III-V compound semiconductor layer located at a side opposite to that of the active layer, convex portions composed of a dielectric substance having a refractive index of 1.0 to 2.3 are buried, and in the fifth nitride-based III-V compound semiconductor layer, dislocation generated from between the convex portions in said one major surface in a direction perpendicular to said one major surface extends to an inclined surface of a triangle portion using a part between the convex portions as the base or to the vicinity of the inclined surface and is then bent in a direction parallel to said one major surface.
In the thirteenth and the fourteenth embodiments of the present invention, the electronic apparatus includes light-emitting diode backlights (such as a backlight for liquid crystal displays), light-emitting diode illuminating devices (besides interior and exterior illuminating devices, such as head lights for automobiles, motorcycles, and the like, and flash lamps for cameras), and light-emitting diode displays, and also includes projectors, rear projection televisions, grating light valves, and the like, which use the light-emitting diode as a light source. In general, an apparatus including at least one light-emitting diode for display, illumination, optical communication, optical transmission, and the like may be basically regarded as the electronic apparatus, and portable and stationary type apparatuses are also regarded as the electronic apparatuses. Besides the apparatuses mentioned above, as concrete examples, there may be mentioned by way of example a mobile phone, a mobile apparatus, a robot, a personal computer, an in-car apparatus, various home electric appliances, light-emitting diode optical communication device, light-emitting diode light transmission device, and a portable security device such as an electronic key. In addition, in the electronic apparatus, an apparatus containing at least two types of light-emitting diodes is also included which emit at least two types of light having different wavelength regions from each other, which may be selected from a far infrared wavelength region, an infrared wavelength region, a red wavelength region, a yellow wavelength region, a green wavelength region, a blue wavelength region, a violet wavelength region, a ultraviolet wavelength region, and the like. In particular, by the light-emitting diode illuminating device, when at least two types of light-emitting diodes emitting visible light having different wavelength regions, such as a red wavelength region, a yellow wavelength region, a green wavelength region, a blue wavelength region, and a violet wavelength region, are combined with each other, and when at least two types of light emitted from the light-emitting diodes are mixed together, natural or white light can be obtained. In addition, when a light-emitting diode emitting light of at least one wavelength region selected from a blue wavelength region, a violet wavelength region, a ultraviolet wavelength region, and the like is used as a light source, and when a phosphor is irradiated with light emitted from the above light-emitting diode for excitation, by mixing at least two types of light obtained thereby, natural or white light can be obtained. In addition, light-emitting diodes emitting visible light of the same wavelength region or different wavelength regions from each other may be assembled to form a cell unit, a quartet unit, or a cluster unit (the number of light-emitting diodes contained in the aforementioned unit is not strictly defined, and when a plurality of equal groups each containing light-emitting diodes having the same wavelength or different wavelengths is formed and is mounted on a wiring board, a wiring package, a wiring housing wall, or the like, the above group is called the unit). That is, in particular, for example, three light-emitting diodes (such as one red light-emitting diode, one green light-emitting diode, and one blue light-emitting diode), four light-emitting diodes (such as one red light-emitting diode, two green light-emitting diodes, and one blue light-emitting diode), or at least five light-emitting diodes may be assembled together to form one unit, and a plurality of the units thus formed may then be mounted on a substrate, a plate, or a housing plate to form a two-dimensional array matrix, one-line pattern, or multiple-line pattern.
In accordance with a fifteenth embodiment of the present invention, there is provided a light-emitting diode comprising; a substrate provided with convex portions on one major surface, the convex portions being composed of a dielectric substance which is different from the substrate and which can change its refractive index by applying a voltage thereto; a fifth nitride-based III-V compound semiconductor layer grown on the substrate without forming a space in a concave portion on the substrate; and a first conductive type third nitride-based III-V compound semiconductor layer, an active layer, and a second conductive type fourth nitride-based III-V compound semiconductor layer, which are provided on the fifth nitride-based III-V compound semiconductor layer; wherein in the fifth nitride-based III-V compound semiconductor layer, dislocation generated from the interface with the bottom surface of the concave portion in a direction perpendicular to said one major surface extends to an inclined surface of a triangle portion using the bottom surface of the concave portion as the base or to the vicinity of the inclined surface and is then bent in a direction parallel to said one major surface.
In accordance with a sixteenth embodiment of the present invention, there is provided a light-emitting diode comprising: a fifth nitride-based III-V compound semiconductor layer; and a first conductive type third nitride-based III-V compound semiconductor layer, an active layer, and a second conductive type fourth nitride-based III-V compound semiconductor layer, which are provided on the fifth nitride-based III-V compound semiconductor layer. In the light-emitting diode described above, in one major surface of the fifth nitride-based III-V compound semiconductor layer located at a side opposite to that of the active layer, convex portions composed of a dielectric substance which can change its refractive index by applying a voltage thereto are buried, and in the fifth nitride-based III-V compound semiconductor layer, dislocation generated from between the convex portions in said one major surface in a direction perpendicular to said one major surface extends to an inclined surface of a triangle portion using a part between the convex portions as the base or to the vicinity of the inclined surface and is then bent in a direction parallel to said one major surface.
In the fifteenth and the sixteenth embodiments of the present invention, as the dielectric substance forming the convex portions and capable of changing its refractive index by voltage application, any material may be basically used, and in particular, for example, there may be used a ferroelectric substance, such as lithium niobate, lithium tantalate, or lanthanum-doped lead zirconate titanate, which preferably does not remarkably absorb light of a light-emitting wavelength. As this ferroelectric substance, besides a material having a stoichiometric composition, a material having a composition slightly deviated therefrom may also be used.
The light-emitting diodes of the fifteenth and the sixteenth embodiment of the present invention may be manufactured by a method similar to that of the first and third embodiments of the present invention. In addition, the fifteenth and the sixteenth embodiments of the present invention may be variously used in a manner similar to that of the second and the fourth embodiment of the present invention.
According to the structures described above of the embodiments of the present invention, when the refractive index of the dielectric substance forming the convex portions is appropriately selected, the far-field pattern of the light-emitting diode can be controlled without using an optical component such as a lens, and when the refractive index is optimized, the light extraction efficiency and the light-scattering property can both be improved. In addition, since the growth of the first nitride-based III-V compound semiconductor layer is started from the bottom surface of the concave portion on the substrate, and the first nitride-based III-V compound semiconductor layer is grown through the state of the triangle cross-sectional shape using the bottom surface of the concave portion as the base, the concave portion can be filled without forming any spaces. Subsequently, from the first nitride-based III-V compound semiconductor layer thus grown, the second nitride-based III-V compound semiconductor layer is grown in the lateral direction. In this step, in the first nitride-based III-V compound semiconductor layer, dislocation is generated from the interface with the bottom surface of the concave portion on the substrate in a direction perpendicular to one major surface of the substrate and then extends to the inclined surface of the first nitride-based III-V compound semiconductor layer or to the vicinity of the inclined surface, and as the second nitride-based III-V compound semiconductor layer is grown, this dislocation is bent in a direction parallel to the major surface of the substrate. When the second nitride-based III-V compound semiconductor layer is grown to have a sufficient thickness, a portion above the dislocation parallel to the major surface of the substrate becomes a region having a significantly low dislocation density. In addition, by the method described above, the first to the fourth nitride-based III-V compound semiconductor layers can be grown by one epitaxial growth. Furthermore, compared to the case in which a concavo-convex structure is directly formed in a substrate by dry etching or the like, the convex portions can be very easily formed on the substrate using a dielectric substance different therefrom, and the process accuracy is also generally high.
According to the embodiments of the present invention, since the refractive index of the dielectric substance forming the convex portions is optimized, and in addition, since spaces between the substrate and the first and/or the second nitride-based III-V compound semiconductor layer are not formed, the light extraction efficiency of the light-emitting diode can be significantly improved. Furthermore, since the crystallinity of the second nitride-based III-V compound semiconductor layer is improved, the crystallinities of the third nitride-based III-V compound semiconductor layer, the active layer, and the fourth nitride-based III-V compound semiconductor layer, which are provided on the second nitride-based III-V compound semiconductor layer, are also significantly improved; hence, the internal quantum efficiency of the light-emitting diode can be improved. Hence, a light-emitting diode having significantly superior luminous efficiency can be obtained. Furthermore, since the light-emitting diode can be manufactured by only one epitaxial growth, the manufacturing cost is low. In addition, the concavo-convex process can be easily performed on the substrate, and the process accuracy is also high. Accordingly, by using the light-emitting diodes having a high luminous efficiency, for example, light source cell units, light-emitting diode backlights, light-emitting diode illuminating devices, light-emitting diode displays, light-emitting diode optical communication devices, optical space transmission devices, and various electronic apparatuses, each having high performance, can be realized.
Hereinafter, the embodiments of the present invention will be described with reference to the accompanying drawings. In all the drawings of the embodiments, the same reference numerals designate the same or corresponding parts.
In this first embodiment, as shown in
In order to form the convex portions 12 each having an isosceles triangle on the substrate 11, a related known technique may be used. For example, by a CVD method, a vacuum deposition method, or a sputtering method, a dielectric film used as a material for the convex portions 12 is formed over the entire surface of the substrate 11. Next, a resist pattern having a predetermined shape is formed on this dielectric film by lithography. Subsequently, by a reactive ion etching (RIE) method or the like, under the conditions in which a taper etching can be performed, this dielectric film is etched using this resist pattern as a mask, so that the convex portions 12 each having an isosceles triangle cross-sectional shape can be formed.
Next, after surfaces of this substrate 11 and the convex portions 12 are cleaned by thermal cleaning or the like, a GaN buffer layer, an AlN buffer layer, a CrN buffer layer, a Cr-doped GaN buffer layer, or a Cr-doped AlN buffer layer (not shown) is formed on this substrate 11 by a related known method at a growth temperature of approximately 550° C. or the like. Subsequently, epitaxial growth of a nitride-based III-V compound semiconductor is performed, for example, by an MOCVD method. This nitride-based III-V compound semiconductor is, for example, GaN. In this case, as shown in
Subsequently, when the nitride-based III-V compound semiconductor is grown while the facet plane orientation of the inclined surface is maintained, as shown in
Next, when the growth conditions are set so that lateral direction growth preferentially occurs, and the growth is further advanced, as shown in
When the lateral direction growth is further continued, as shown in
Subsequently, as shown in
In addition, depending on the case, from the state shown in
Next, as shown in
Subsequently, the substrate 11 on which the nitride-based III-V compound semiconductor layers are formed as described above is recovered from an MOCVD apparatus.
Next, a p-side electrode 19 is formed on the p-type nitride-based III-V compound semiconductor layer 18. As a material for the p-side electrode 19, an ohmic metal having a high reflectance to light having a light-emitting wavelength is preferably used.
Subsequently, in order to activate a p-type impurity of the p-type nitride-based III-V compound semiconductor layer 18, for example, in a mixed gas atmosphere containing N2 and O2 (containing, for example, 99% of N2 and 1% of O2), heat treatment is performed at 550 to 750° C. (such as 650° C.) or 580 to 620° C. (such as 600° C.). In this step, for example, by mixing N2 and O2, activation can be easily obtained. In addition, for example, as a raw material for F, Cl, or the like, which has a high electronegativity similar to that of O and N, a halogenated nitride (NF3, NCl3, or the like) may be mixed in an N2 atmosphere or a mixed gas atmosphere of N2 and O2. The time for this heat treatment is, for example, 5 minutes to 2 hours or 40 minutes to 2 hours, or is generally approximately 10 to 60 minutes. The reason the heat treatment is performed at a relatively low temperature is to prevent the degradation of the active layer 17 during the heat treatment. In addition, this heat treatment may be performed after the p-type nitride-based III-V compound semiconductor layer 18 is epitaxially grown and before the p-side electrode 19 is formed.
Subsequently, the n-type nitride-based III-V compound semiconductor layer 16, the active layer 17, and the p-type nitride-based III-V compound semiconductor layer 18 are patterned into a predetermined shape by an RIE method, a powder blast method, a sandblast method, or the like, so that a mesa portion 20 is formed.
Next, on part of the n-type nitride-based III-V compound semiconductor layer 15 adjacent to this mesa portion 20, an n-side electrode 21 is formed.
Subsequently, whenever necessary, after the substrate 11 on which the light-emitting diode structure is formed as described above is polished or lapped from the rear surface side to decrease the thickness, scribing of this substrate 11 is performed, so that bars are formed. Next, the bars are scribed, so that chips are formed.
By the steps as described above, an intended light-emitting diode can be manufactured.
The planar shapes of the p-side electrode 19 and the n-side electrode 21 are shown by way of example in
As raw materials of the above nitride-based III-V compound semiconductor layers, for example, triethylgallium ((C2H5)3Ga, TEG) or trimethylgallium ((CH3)3Ga, TMG) is used as a raw material for Ga; trimethylaluminum ((CH3)3Al, TMA) is used as a raw material for Al; triethylindium ((C2H5)3In, TEI) or trimethylindium ((CH3)3In, TMI) is used as a raw material for In; and ammonia (NH3) is used as a raw material for N. As for a dopant, for example, silane (SiH4) or disilane (Si2H6) is used as an n-type dopant; bis(methylcyclopentadienyl)magnesium ((CH3C5H4)2Mg), bis(ethylcyclopentadienyl)magnesium ((C2H5C5H4)2Mg), or bis(cyclopentadienyl)magnesium ((C5H5)2Mg) is used as a p-type dopant. In addition, as a carrier gas atmosphere during the growth of the nitride-based III-V compound semiconductor layers, for example, a H2 gas is used.
A particular structural example of this light-emitting diode will be described. That is, for example, the nitride-based III-V compound semiconductor layer 15 is an n-type Gan layer, the n-type nitride-based III-V compound semiconductor layer 16 is formed of an n-type GaN layer and an n-type GaInN layer in that order from the bottom, and the p-type nitride-based III-V compound semiconductor layer 18 is formed of a p-type AlInN layer, a p-type GaN layer, and a p-type GaInN layer in that order from the bottom. The active layer 17 has, for example, a GaInN-based multiquantum well (MQW) structure (for example, a GaInN quantum well layer and a GaN barrier layer are alternately laminated to each other), and the In composition of this active layer 17 is selected in accordance with a light-emitting wavelength of the light-emitting diode and is, for example, 11% or less at a light-emitting wavelength of 405 nm, 18% or less at a wavelength of 450 nm, and 24% or less at a wavelength of 520 nm. As a material for the p-side electrode 19, for example, Ag or Pd/Ag is used, or whenever necessary, besides the above metal, a barrier metal containing Ti, W, Cr, WN, CrN, or the like is used. As the n-side electrode 21, for example, a Ti/Pt/Au structure may be used.
In the light-emitting diode shown in
In this first embodiment, in order to minimize the threading dislocation density of the nitride-based III-V compound semiconductor layer 15, the width Wg of the bottom of the concave portion 13, the depth thereof, that is, the height d of the convex portion 12, and the angle α formed between the major surface of the substrate 11 and the inclined surface of the nitride-based III-V compound semiconductor layer 15 in the state shown in
2 d>Wg·tan α
For example, when Wg is 2.1 μm and α is 59°, d is 1.75 μm or more; when Wg is 2 μm and α is 59°, d is 1.66 μm or more; when Wg is 1.5 μm and α is 59°, d is 1.245 μm or more; and when Wg is 1.2 μm and α is 59°, d is 0.966 μm or more. However, in all the cases, d is preferably set to less than 5 μm.
When the nitride-based III-V compound semiconductor layer 15 is grown in the steps shown in
In
Ga(CH3)3 (g)+3/2 H2 (g)→Ga (g)+3CH4 (g) NH3 (g)→(1−α)NH3 (g)+α/2 N2 (g)+3α/2 H2 (g) Ga (g)+NH3 (g)=GaN (s)+3/2 H2 (g)
According to this reaction, H2 gas is generated, and this H2 gas has as an opposite function, that is, has an etching function. In the steps shown in
In
In addition, in
In
Next, the growth behavior of the nitride-based III-V compound semiconductor layer 15 from the early growth stage and the propagation behavior of dislocations will be described with reference to
When the growth starts, as shown in
With reference to
Next, the difference in behavior of the dislocations generated in the nitride-based III-V compound semiconductor layer will be described between the case in which the minute nuclei 14 are generated at the early growth stage and the case in which the minute nuclei 14 are not generated.
As described above, according to this first embodiment, since a dielectric substance having a refractive index of 1.7 to 2.2 is used as a material for the convex portions 12, the light extraction efficiency of the light-emitting diode can be maximized. In addition, since spaces are not formed between the substrate 11 and the nitride-based III-V compound semiconductor layer 15, the decrease in light extraction efficiency caused by the spaces can be prevented. In addition, since the threading dislocations of the nitride-based III-V compound semiconductor layer 15 are concentrated in the vicinity of the central portion of the convex portion 12, and the dislocation density of the other portions is, for example, approximately 6×107/cm2, which is significantly decreased as compare to that in the case using a related concavo-convex processed substrate, the crystallinity of the nitride-based III-V compound semiconductor layer 15 and that of the nitride-based III-V compound semiconductor layers, such as the active layer 17, formed thereon are significantly improved, and the number of non-luminescent centers is significantly decreased, so that the internal quantum efficiency is improved. Accordingly, a nitride-based III-V compound semiconductor light-emitting diode having a significantly high luminous efficiency can be obtained.
In addition, epitaxial growth for manufacturing this nitride-based III-V compound semiconductor light-emitting diode may be performed only one time, and a growth mask is not used. Furthermore, since the convex portions 12 on the substrate 11 can be formed only by forming a dielectric film using a material for the convex portions 12 and then processing this dielectric film by an etching method, a powder blast method, a sand blast method, or the like, the substrate 11, such as a sapphire substrate, which is difficult to be processed, may not be processed, and the manufacturing process can be simplified; hence, as a result, the nitride-based III-V compound semiconductor light-emitting diode can be manufactured at a reasonable cost.
Next, a second embodiment of the present invention will be described.
In this second embodiment, when the nitride-based III-V compound semiconductor layer 15 is grown to have an isosceles triangle cross-sectional shape using the bottom surface of the concave portion 13 as the base, the height of the convex portion 12 is selected so that the height of this nitride-based III-V compound semiconductor layer 15 is lower than that of the convex portion 12. As one example, in
The configuration other than that described above is similar to that in the first embodiment.
According to this second embodiment, since the nitride-based III-V compound semiconductor layer 15 having a threading dislocation density of substantially zero can be grown, a nitride-based III-V compound semiconductor substrate having substantially no dislocation can be obtained. In addition, for example, when the n-type nitride-based III-V compound semiconductor layer 16, the active layer 17, and the p-type nitride-based III-V compound semiconductor layer 18 are grown on this nitride-based III-V compound semiconductor substrate having substantially no dislocation, the dislocation densities of the layers described above can be significantly decreased, and as a result, a nitride-based III-V compound semiconductor light-emitting diode having significantly superior properties can be advantageously obtained. In addition, of course, advantages similar to those in the first embodiment can also be obtained.
Next, a third embodiment of the present invention will be described.
In this third embodiment, after the p-side electrode 19 is formed through the process similar to that in the first embodiment, without forming the mesa portion 20 in the n-type nitride-based III-V compound semiconductor layer 16, the active layer 17, and the p-type nitride-based III-V compound semiconductor layer 18, the substrate 11 is removed, so that the rear surface of the n-type nitride-based III-V compound semiconductor layer 15 is exposed. Subsequently, as shown in
In this case, as the material for the convex portions 12, a dielectric substance having a refractive index of 1.0 to 2.3, in particular, such as CeO2, HfO2, Ta2O5, Y2O3, ZnO, ZrO2, rhombic sulfur, LiTaO3, LiNbO3, AlON, SiO, Si3N4, Al2O3, BeO, MgO, SiO2, LiF, CaF2, MgF2, NaF, AlF3, CeF3, LaF3, or NdF3, may be used and, for example, may be appropriately selected therefrom.
In addition, since the entire thickness of the light-emitting diode is significantly decreased by removing the substrate 11, in order to improve the mechanical strength, as shown in
The configuration other than that described above is similar to that in the first embodiment.
According to this third embodiment, the flip chip type light-emitting diode obtained by removing the substrate 11 has advantages similar to those of the first embodiment. In addition, since the n-side electrode 21 is formed approximately over the entire rear surface of the nitride-based III-V compound semiconductor layer 15, the generation of a current crowing phenomenon during light-emitting diode operation can be prevented, and in particular, increase in output, increase in brightness, and increase in area of the light-emitting diode can be advantageously performed.
Next, a fourth embodiment of the present invention will be described.
In this fourth embodiment, as shown in
Next, in a manner similar to that in the first embodiment, the nitride-based III-V compound semiconductor layer 15 is grown. In particular, through the process including the generation, the growth, and the coalescence of the minute nuclei 14 on the bottom surface of the concave portion 13, as shown in
Subsequently, in a manner similar to that in the first embodiment, the steps are sequentially performed, and as shown in
The configuration other than that described above is similar to that described in the first embodiment.
In
A light-emitting diode was formed by using Si3N4 having a refractive index of 2.0 as a dielectric substance forming the convex portions 12. As a comparative example, a light-emitting diode was formed by using SiO2 having a refractive index of 1.46 as a dielectric substance forming the convex portions 12. The shape and the arrangement of the convex portions 12 were the same as those shown in
Next, a fifth embodiment according to the present invention will be described.
In this fifth embodiment, after the p-side electrode 19 is formed through the process similar to that in the fourth embodiment, without forming the mesa portion 20 in the n-type nitride-based III-V compound semiconductor layer 16, the active layer 17, and the p-type nitride-based III-V compound semiconductor layer 18, the substrate 11 is removed, so that the rear surface of the n-type nitride-based III-V compound semiconductor layer 15 is exposed. Subsequently, as shown in
In this case, as the material for the convex portions 12, a dielectric substance having a refractive index of 1.0 to 2.3 may be used as is the case of the third embodiment.
In addition, since the entire thickness of the light-emitting diode is significantly decreased by removing the substrate 11, in order to improve the mechanical strength, as is the case shown in
The configuration other than that described above is similar to that in the fourth embodiment.
According to this fifth embodiment, advantages similar to those obtained in the third embodiment can be obtained.
Next, a sixth embodiment according to the present invention will be described.
In this sixth embodiment, after the mesa portion 20 is formed through the process similar to that in the fourth embodiment, the substrate 11 is removed, so that the rear surface of the n-type nitride-based III-V compound semiconductor layer 15 is exposed. The planar shape and arrangement of the convex portions 12 are the same as those shown in
Next, as shown in
Next, as shown in
Next, as shown in
Subsequently, as shown in
In the case described above, as the material for the convex portions 12, a dielectric substance capable of changing the refractive index by applying a voltage, in particular, such as lithium niobate, lithium tantalate, or lanthanum-doped lead zirconate titanate, may be used, and for example, may be appropriately selected therefrom.
According to this sixth embodiment, as shown in
Next, a seventh embodiment of the present invention will be described.
In this seventh embodiment, a process similar to that in the first embodiment was performed until the step of forming the p-side electrode 19, and steps thereafter are different from those in the first embodiment. In this embodiment, a technique is preferably applied to this p-side electrode 19 in which a layer containing Pd is provided to prevent diffusion of an electrode material (such as Ag), and/or in order to prevent the generation of defects caused, for example, by stress, heat, and/or diffusion of Au or Sn to the p-side electrode 19 from a layer (solder layer, bump, or the like) which contains Au or Sn and which is formed at an upper side, a layer composed of a high melting point metal, such as Ti, W, Cr, or an alloy thereof, or composed of a metal nitride thereof (TiN, WN, TiWN, CrN, or the like) is further formed on the above Pd-containing layer so as to be used as an amorphous barrier metal layer having no grain boundaries. As for the technique providing a layer containing Pd, a Pd interstitial layer is known, for example, in a metal plating technique, and the above barrier layer material is well known, for example, in an Al wiring technique or a Ag wiring technique for Si-based electronic devices.
In addition, in this embodiment, in order to protect the p-side electrode 19 which is directly in contact with the p-type nitride-based III-V compound semiconductor layer 18 and which has inferior resistance against thermal stress, an example is disclosed in which a high melting point metal, such as Ti, W, Cr, or an alloy thereof, or a nitride of the aforementioned metal is provided to form a protective layer. However, since this protective layer itself can be used as an electrode in direct contact with the p-type nitride-based III-V compound semiconductor layer 18 and has stress resistance and an adhesion enhancing force, besides the electrode at the p-type nitride-based III-V compound semiconductor layer 18 side, it may also be used as an n-side electrode for the first layer instead of a Ti/Pt/Au electrode which has been used as the n-side electrode 21 in contact with the n-type nitride-based III-V compound semiconductor layer 15. As a method using an adhesion enhancing force, for example, a substrate bonding technique may be used at the p side and/or the n side to enhance a bonding strength of a metal-metal bonding portion, a metal-dielectric substance bonding portion, or the like. As one particular example for obtaining stress resistance and/or adhesion enhancing force, when an outermost surface of the p-side electrode 19 composed of a monolayer metal film or a multilayer metal film is formed of Au, after a high melting point metal film of Ti, W, Cr, or an alloy thereof, or a nitride of the aforementioned metal is formed on a conductive support substrate, a Au film is further formed on the film described above, and this Au film can be bonded to the p-side electrode 19.
That is, in this seventh embodiment, as shown in
Next, as shown in
Next, as shown in
Subsequently, as shown in
Next, as shown in
Subsequently, as shown in
Next, as shown in
Next, as shown in
Subsequently, as shown in
Next, as shown in
Next, whenever necessary, after the rear surface of the substrate 11 on which the light-emitting diode structure is formed as described above is polished or lapped to decrease the thickness, this substrate 11 is scribed to form bars. Subsequently, this bar is scribed to form chips.
The electrode lamination structure of the light-emitting diode described with reference to
Next, an eighth embodiment of the present invention will be described.
In this eighth embodiment, the case will be described in which a light-emitting diode backlight is manufactured by using a red light-emitting diode (such as an AlGaInP-based light-emitting diode), which is separately prepared, together with a blue light-emitting diode and a green light-emitting diode obtained by the method according to the first embodiment.
After blue light-emitting diode structures are formed on the substrate 11 by the method according to the first embodiment, and bumps (not shown) are then formed on the corresponding p-side electrodes 19 and n-side electrodes 21, the substrate 11 is scribed to form chips, so that flip chip type blue light-emitting diodes are obtained. In a manner similar to that described above, flip chip type green light-emitting diodes are obtained. In addition, diode structures are formed by laminating AlGaInP-based semiconductor layers on an n-type GaAs substrate, followed by forming p-side electrodes on the laminate, so that chip-type AlGaInP-based light-emitting diodes are each obtained as a red light-emitting diode.
Subsequently, the red light-emitting diode chip, the green light-emitting diode chip, and the blue light-emitting diode chip are mounted on respective submounts made of AlN or the like and are then mounted at predetermined positions on a substrate, such as an Al substrate, so that the submounts are brought into contact with the substrate. This state is shown in
However, without using the submounts 62, the red light-emitting diode chip 63, the green light-emitting diode chip 64, and the blue light-emitting diode chip 65 may be directly mounted on an arbitrary printed circuit board having heat dissipation properties, or on a plate or an internal or an external wall (such as an internal wall of a chassis) having a printed circuit board function, and by this direct mounting, the cost of the light-emitting diode backlight or the cost of the entire panel can be reduced.
As described above, the red light-emitting diode chip 63, the green light-emitting diode chip 64, and the blue light-emitting diode chip 65 are used as one unit (cell), and a necessary number of the cells is disposed on the substrate 61 in a predetermined pattern. One pattern example is shown in
This light-emitting diode backlight is preferably used, for example, for a backlight for liquid crystal panels.
Next, a ninth embodiment of the present invention will be described.
In this ninth embodiment, as is the eighth embodiment, after a necessary number of cells each containing the red light-emitting diode chip 63, the green light-emitting diode chip 64, and the blue light-emitting diode chip 65 is disposed on the substrate 61 in a predetermined pattern, as shown in
This light-emitting diode backlight is preferably used, for example, for a backlight for liquid crystal panels.
Next, a tenth embodiment of the present invention will be described.
In this tenth embodiment, the case will be described in which a light source cell unit is manufactured by using a red light-emitting diode, which is separately prepared, together with a blue light-emitting diode and a green light-emitting diode obtained by the method according to the first embodiment.
As shown in
Concrete examples of the arrangement of the cells 75 on the printed circuit board 76 are shown in
In
When at least one light source cell unit described above is disposed, a light-emitting diode backlight can be obtained which is preferably used, for example, as a backlight of liquid crystal panels.
Although the pad electrode portion, the wiring portion, and the like on the printed circuit substrate 76 are generally formed from Au, after those mentioned above are all or partly formed from a high melting point metal, such as Ti, W, Cr, or an alloy thereof, having durability and an adhesion enhancing force or from a nitride of the aforementioned metal, Au may then be formed thereon. The pad electrode portion, the wiring portion, and the like described above may be formed, for example, by electroplating, electroless plating, vacuum deposition (flash deposition), or sputtering using the materials mentioned above. Alternatively, after the pad electrode portion, the wiring portion, and the like are formed from Au, films may be formed thereon using the materials mentioned above. In addition, for example, the following may also be performed. That is, after the pad electrode portion, the wiring portion, and the like are formed from a high melting point metal, such as Ti, W, Cr, or an alloy thereof, and are then nitrided, a high melting point metal, such as Ti, W, Cr, or an alloy thereof, is again deposited thereon so that the surface is placed in the state before nitridation, and on the surface thereof, the light-emitting diode chips 63 to 65 may be die-bonded from TiW electrode or Au electrode sides with films of Ti, W, Cr, Au, or the like interposed therebetween, whenever necessary.
In addition, when a protective chip (circuit), a base-opened transistor element (circuit), a trigger diode element (circuit), a negative resistance element (circuit), and the like are mounted which are to be connected to the light-emitting diode chips 63 to 65 mounted on the printed circuit board 76, in order to improve the reliability, such as adhesion strength and heat-stress resistance, of the light source cell, the above electrode structure using a high melting point metal such as Ti, W, Cr, or an alloy thereof, or a nitride of the aforementioned metal may also be used.
In addition, on areas on the printed circuit board 76 other than those on which the transparent resins 68 to 71 are potted, a white resist may be applied as thick as possible so as to suppress light emitted from the light-emitting diode chips 63 to 65 from being absorbed by the printed circuit board 76.
Heretofore, although the embodiments of the present invention are particularly described, the present invention is not limited to the above embodiments, and various modifications may be made without departing from the sprit and the scope of the present invention.
For example, the numeric values, materials, structures, shapes, substrates, raw materials, processes, directions of the convex portions 12 and the concave portions 13, and the like of the first to the tenth embodiments are described by way of example, and whenever necessary, numeric values, materials, structures, shapes, substrates, raw materials, processes, and the like different from those described above may be used.
In particular, for example, in the above first to tenth embodiments, the conductance of the p-type conductive layer and that of the n-type conductive layer may be set opposite to each other.
Furthermore, whenever necessary, at least two of the first to the tenth embodiments may be used in combination.
It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-316885 | Nov 2006 | JP | national |
