Patent Application
20140239251
This application claims the benefit of Japanese Priority Patent Application JP 2013-034821 filed Feb. 25, 2013, the entire contents of which are incorporated herein by reference.
The present disclosure relates to a semiconductor light emitting element and a display device including the semiconductor light emitting element.
A display device, such as a projector device including a semiconductor light emitting element formed of a semiconductor laser element as a light source, that is, a so-called laser display device, has been disclosed, for example, in Japanese Unexamined Patent Application Publication No. 2009-025462. Since being compact and lightweight and having a feature of low electrical power consumption besides a high luminance and a high definition, the laser display device has drawn significant attention. However, in the laser display device, a speckle noise has been partially but not totally responsible for degradation in quality of various types of images. This speckle noise is generated by a phenomenon in which because of a high coherence of laser light, scattered light beams thereof interfere with each other on a laser irradiation surface, such as a screen or a wall surface, on which various types of images are to be displayed, and this phenomenon is caused by the presence of fine irregularities of the laser irradiation surface. Incidentally, a speckle contrast C can be represented by the following equation (1) when the wavelength of laser light, the surface roughness of the laser irradiation surface, and the oscillation wavelength width of laser light are represented by λ, σh, and Δλ, respectively. In addition, it is found that from the equation (1), as the value of the oscillation wavelength width Δλ is increased, the reduction in speckle noise can be performed.
C=[1/{2(2·π·σh·Δλ/λ2)2+1}]1/4 (1)
A semiconductor light emitting element which reduces a speckle noise has been disclosed in Japanese Unexamined Patent Application Publication No. 2010-171316. The semiconductor light emitting element disclosed in the above patent document includes: an active multimode waveguide which allows light in a fundamental transverse mode and light in a first-order transverse mode to pass therethrough; and an active layer having a first active layer region in which the fundamental transverse mode is distributed more than the first-order transverse mode and a second active layer region in which the first-order transverse mode is distributed more than the fundamental transverse mode. In addition, in this semiconductor light emitting element described above, the light emission wavelength of the first active layer region is different from that of the second active layer region.
In the semiconductor light emitting element disclosed in Japanese Unexamined Patent Application Publication No. 2010-171316, the fundamental transverse mode and the first-order transverse mode are alternately oscillated. In this case, since the oscillation wavelengths are different from each other, the oscillation spectrum is widened on the time-average basis, the coherence of laser light is reduced, and hence the speckle noise can be reduced. However, since the optical intensity distribution of the first-order transverse mode is not the normal distribution, the light collection properties are degraded, and as a result, a highly fine image may not be disadvantageously obtained.
Accordingly, it is desirable to provide a semiconductor light emitting element which emits light, the optical intensity distribution of which is the normal distribution, and which can display a highly fine image, and it is also desirable to provide a display device including the semiconductor light emitting element described above.
According to a first embodiment of the present disclosure, there is provided a semiconductor light emitting element in which first regions and second regions are periodically and alternately arranged in an optical waveguide along an extending direction thereof; when the number of the first regions and the number of the second regions are represented by P1 and P2, respectively, if (P1−P2)=1 holds, P2 is an integer of 2 or more, and if (P2−P1)=1 holds, P1 is an integer of 2 or more; and an effective refractive index of the first region is different from an effective refractive index of the second region.
According to a second embodiment of the present disclosure, there is provided a semiconductor light emitting element in which first regions and second regions are periodically and alternately arranged in an optical waveguide along an extending direction thereof; when the number of the first regions and the number of the second regions are represented by P1 and P2, respectively, if (P1−P2)=1 holds, P2 is an integer of 2 or more, and if (P2−P1)=1 holds, P1 is an integer of 2 or more; and the width of the first region is different from the width of the second region.
According to a third embodiment of the present disclosure, there is provided a semiconductor light emitting element in which first regions and second regions are periodically and alternately arranged in an optical waveguide along an extending direction thereof; when the number of the first regions and the number of the second regions are represented by P1 and P2, respectively, if (P1−P2)=1 holds, P2 is an integer of 2 or more, and if (P2−P1)=1 holds, P1 is an integer of 2 or more; and two types of light in a fundamental transverse mode are emitted.
According to a fourth embodiment of the present disclosure, there is provided a display device including one of the semiconductor light emitting elements according to the first to the third embodiments of the present disclosure.
In the semiconductor light emitting element according to the first embodiment of the present disclosure, the first regions and the second regions are periodically and alternately arranged, and the effective refractive index of the first region is different from the effective refractive index of the second region, and in the semiconductor light emitting element according to the second embodiment of the present disclosure, the first regions and the second regions are periodically and alternately arranged, and the width of the first region is different from the width of the second region; hence, a wavelength λ2 of light in a fundamental transverse mode generated in the second region is different from a wavelength λ1 of light in a fundamental transverse mode generated in the first region. In addition, in the semiconductor light emitting element according to the third embodiment of the present disclosure, in the first regions and the second regions, the two types of light in a fundamental transverse mode are generated. In this case, the value of P1 or P2 is an integer of 2 or more. Incidentally, when light in a fundamental transverse mode generated in one of the first region and the second region is propagated through the other region of the optical waveguide, the light is coupled with light in a fundamental transverse mode generated in the other region (energy conversion is performed). That is, for example, light in a fundamental transverse mode generated in the second region is generally absorbed, in a way, in light in a fundamental transverse mode generated in the first region. Hence, in the semiconductor light emitting elements according the first to the third embodiments of the present disclosure, for example, if (P1−P2)=1 holds, since at least two second regions are present, light in a fundamental transverse mode generated in one second region reaches an adjacent second region before coupling with light in a fundamental transverse mode generated in the first region is completed. As a result, two types of light in a fundamental transverse mode (light having a wavelength λ1 and light having a wavelength λ2) can be present. Accordingly, the value of the wavelength width Δλ of the total light emitted from the semiconductor light emitting element can be increased. Hence, without using a complicated element structure and/or circuit, by the above equation (1), the speckle noise can be reduced by the semiconductor light emitting element itself. In addition, since the light generated in the first region and the light generated in the second region are each in a fundamental transverse mode, the optical intensity distribution of the total light to be emitted is the normal distribution, and hence a highly fine image can be obtained.
Hereinafter, with reference to the drawings, although the present disclosure will be described using examples, the present disclosure is not limited thereto, and various numerical values and materials disclosed in the examples are merely shown by way of example. In addition, description will be made in the following order.
[Description relating to the semiconductor light emitting elements according to the first to the third embodiments of the present disclosure, the display device according to the fourth embodiment of the present disclosure, and the others]
In the following description, the semiconductor light emitting elements according to the first, the second, and the third embodiments of the present disclosure and the semiconductor light emitting element included in the display device according to the fourth embodiment of the present disclosure may be collectively referred to, for example, as the “semiconductor light emitting element according to an embodiment of the present disclosure” in some cases.
The semiconductor light emitting element according to the first or the second embodiment of the present disclosure may be configured to emit two types of light in a fundamental transverse mode.
In the semiconductor light emitting element according to the first embodiment of the present disclosure including the above preferable configuration, when the length of the first region along the extending direction of the optical waveguide is represented by L1, the average wavelength of light to be emitted is represented by λave, the effective refractive index of the first region is represented by neff-1, and the effective refractive index of the second region is represented by neff-2, the following equation is preferably satisfied.
0.7×{λave/(neff-1−neff-2)}≦L1≦1.3×{λave/(neff-1−neff-2)}
In the semiconductor light emitting element according to the first embodiment of the present disclosure including the preferable configuration described above, when the effective refractive index of the first region is represented by neff-1, and the effective refractive index of the second region is represented by neff-2, the following equation is preferably satisfied.
1×10−3≦(neff-1−neff-2)/neff-1≦1.33 10−2
When the value of {(neff-1−neff-2)/neff-1} is excessively increased, light in a fundamental transverse mode may not be emitted, the intensity distribution of light beams emitted from the semiconductor light emitting element is deviated from the normal distribution, the light collection properties are degraded, and as a result, a highly fine image may not be obtained in some cases. Hence, the value of {(neff-1−neff-2)/neff-1} is preferably set as described above so that a higher-order transverse mode is not generated.
In addition, in the semiconductor light emitting element according to the second embodiment of the present disclosure including the above preferable configuration, when the width of the first region and the width of the second region are represented by W1 and W2, respectively, the following equation is preferably satisfied.
1.2<W2/W1<2.5
Furthermore, for example, in the semiconductor light emitting element according to an embodiment of the present disclosure including the preferable configuration described above, when the total length of the first regions along the extending direction of the optical waveguide and the total length of the second regions along the extending direction of the optical waveguide are represented by L1 and L2, respectively, the following equation is preferably satisfied.
0.1≦L2/(L1+L2)≦0.4
Furthermore, for example, in the semiconductor light emitting element according to an embodiment of the present disclosure including the preferable configuration described above, when the maximum peak value of the wavelength of light to be emitted from the semiconductor light emitting element and the wavelength width of the light are represented by λmax and Δλ, respectively, in view of reduction in speckle noise, a higher value of Δλ/λmax is more preferable. Although the lower limit of Δλ/λmax is not particularly limited, for example, a value of 1.5×10−4 may be mentioned. When the semiconductor light emitting element is formed of a semiconductor laser element, the maximum peak value λmax of the wavelength of light to be emitted from the semiconductor light emitting element and the wavelength width Δλ of the light correspond to the maximum peak value of the oscillation wavelength and the width thereof, respectively, and when the semiconductor light emitting element is formed of a super luminescent diode, the maximum peak value λmax of the wavelength of light to be emitted from the semiconductor light emitting element and the wavelength width Δλ of the light correspond to the maximum peak value of the emission wavelength and the width thereof, respectively.
Furthermore, in the semiconductor light emitting element according to the first embodiment of the present disclosure including the preferable configuration described above, the structure may be formed in which one ridge portion is occupied with the first regions and the second regions, and in the vicinity of each second region (one side or both sides of the ridge portion), a refractive index control region (a refractive index change region, a refractive index disturbance region, a disorder region, or a waveguide loss decrease region) is provided which makes the effective refractive index of the second region different from the effective refractive index of the first region. In addition, in the refractive index control region, a substance (or a substance/impurity which increases the energy bandgap in the refractive index control region) which decreases the refractive index may be contained. In this case, as the substance which decreases the refractive index, for example, zinc oxide (ZnO) may be mentioned, and when zinc oxide is heat-diffused, an active layer is disordered, and the refractive index can be decreased. Alternatively, the refractive index control region may have the structure formed of a metal film. In this case, as a material forming the metal film, for example, Ti, Pt, and Au may be mentioned, and when those materials are each formed into a film, for example, by a vacuum deposition method or a sputtering method, the refractive index can be decreased. As a method for forming the refractive index control region, the following may be mentioned by way of example.
In addition, in the semiconductor light emitting element according to the second or the third embodiment of the present disclosure including the preferable configuration and structure described above, the structure in which one ridge portion is occupied with the first regions and the second regions may be formed.
Furthermore, for example, in the semiconductor light emitting element according to an embodiment of the present disclosure including the preferable configuration and structure described above, a configuration may be formed in which a predetermined drive current is allowed to pass through the first regions and the second regions of the optical waveguide, and in addition, a high frequency signal (such as 100 to 300 MHz) is superimposed on the current. Accordingly, since fluctuation of the gain is generated, the value of Δλ/λmax can be further increased, and as a result, the reduction in speckle noise can be more effectively achieved.
Furthermore, for example, in the semiconductor light emitting element according to an embodiment of the present disclosure including the preferable configuration and structure described above, a configuration may be formed in which an active layer is provided for the optical waveguide, and the active layer is formed from an AlGaInP-based compound semiconductor, and in this case, the active layer may be configured to have a quantum well structure in which at least one well layer formed of a GaInP layer or an AlGaInP layer and at least two barrier layers each formed of an AlGaInP layer are laminated to each other. Alternatively, a configuration may be formed in which an active layer is provided for the optical waveguide, and the active layer is formed from a GaInN-based compound semiconductor, and in this case, the active layer may be configured to have a quantum well structure in which at lease one well layer formed of a GaInN layer and at least two barrier layers each formed of an GaInN layer having an In composition different from that of the well layer are laminated to each other. A compound semiconductor-laminate structure forming the ridge portion itself may have a common configuration, and in particular, the compound semiconductor-laminate structure is formed on a substrate and includes a first region compound semiconductor layer, an active layer, and a second compound semiconductor layer laminated in this order from a substrate side. A first electrode is connected to the first compound semiconductor layer or the substrate, and a second electrode is connected to the second compound semiconductor layer.
Furthermore, for example, in the semiconductor light emitting element according to an embodiment of the present disclosure including the preferable configuration and structure described above, the semiconductor light emitting element may be formed of a semiconductor laser element or a super luminescent diode (SLD). In this case, in the semiconductor laser element, when the optical reflectance of a light emission surface and the optical reflectance of a light reflection surface are optimized, a resonator may be formed. On the other hand, in the super luminescent diode, when the optical reflectance of a light emission surface is set to a very low value, and the optical reflectance of a light reflection surface is set to a very high value, without forming a resonator, light generated in the active layer is reflected on the light reflection surface and is emitted from the light emission surface. In general, on the light emission surface, an anti-reflection (AR) coating layer or a low-reflection coating layer is formed. In addition, on the light reflection surface, a high-reflection (HR) coating layer is formed. As the anti-reflection coating layer (or the low-reflection coating layer), for example, there may be mentioned a laminate structure formed from at least two types of layers selected from the group consisting of a titanium oxide layer, a tantalum oxide layer, a zirconium oxide layer, a silicon oxide layer, an aluminum oxide layer, an aluminum nitride layer, and a silicon nitride layer.
As the display device according to the fourth embodiment of the present disclosure, for example, a projector device, an image display device, a monitor device, a reflection type liquid crystal display device, a head mount display (HMD), a head up display (HUD), and a laser lighting device, each including a semiconductor light emitting element as a light source, may be mentioned. In addition, the semiconductor light emitting element according to an embodiment of the present disclosure may also be used as a light source of a laser microscope.
As the width W1 of the ridge portion, a width of 1.0 to 2.5 μm may be mentioned by way of example. Since a higher-order transverse mode may be generated in some cases when the width of the ridge portion is excessively large, the widths W1 and W2 of the ridge portion are preferably determined so as not to generate a higher-order transverse mode. In particular, as the upper limit of the width W2, a width of 3.0 μm may be mentioned.
As the substrate, for example, there may be mentioned a GaAs substrate, a GaP substrate, an AIN substrate, an AlP substrate, an InN substrate, an InP substrate, an AlGaInN substrate, an AlGaN substrate, an AlInN substrate, an AlGaInP substrate, an AlGaP substrate, an AlInP substrate, a GaInP substrate, a ZnS substrate, a sapphire substrate, a SiC substrate, an alumina substrate, a ZnO substrate, a LiMgO substrate, a LiGaO2 substrate, an MgAl2O4 substrate, a Si substrate, and a Ge substrate. In addition, a substrate prepared by forming a buffer layer or an intermediate layer on a surface (principal surface) of the substrate mentioned above may also be used. In addition, as for the principal surface of the substrate, depending on the crystalline structure (such as a cubic system or a hexagonal system), a crystalline orientation plane, such as a so-called A plane, B plane, C plane, R plane, M plane, N plane, or S plane, or a plane shifted in a specific direction from any of those planes mentioned above, may also be used.
As an n-type impurity added to the compound semiconductor layer forming the compound semiconductor-laminate structure, for example, Silicon (Si), germanium (Ge), selenium (Se), tin (Sn), carbon (C), tellurium (Te), sulfur (S), oxygen (O), and Pd (palladium) may be mentioned, and as a p-type impurity, zinc (Zn), magnesium (Mg), beryllium (Be), cadmium (Cd), calcium (Ca), and barium (Ba) may be mentioned. The active layer may have either a single quantum well structure [QW structure] or a multiquantum well structure [MQW structure]. As a method for forming the compound semiconductor-laminate structure (film formation method), an organometallic chemical vapor phase growth method (MOCVD method or MOVPE method), an organometallic molecular beam epitaxy method (MOMBE method), a hydride vapor phase epitaxial method (HVPE method) in which a halogen contributes for transportation or reaction, and a plasma assisted physical vapor phase growth method (PPD method) may be mentioned. As a method for etching the compound semiconductor-laminate structure to form the ridge portion, for example, a combination between a lithographic technique and a wet etching technique and a combination between a lithographic technique and a dry etching technique may be mentioned.
The compound semiconductor-laminate structure is connected to the first electrode and the second electrode. When the first electrode or the second electrode is formed on the substrate or the compound semiconductor layer having a p-type conductivity, as the electrode (p-side electrode), for example, there may be mentioned Au/AuZn, Au/Pt/Ti(/Au)/AuZn, Au/AuPd, Au/Pt/Ti(/Au)/AuPd, Au/Pt/TiW(/Ti) (/Au)/AuPd, Au/Pt/Ti, or Au/Ti. In addition, when the first electrode or the second electrode is formed on the substrate or the compound semiconductor layer having an n-type conductivity, as the electrode (n-side electrode), for example, there may be mentioned Au/Ni/AuGe, Au/Pt/Ti(/Au)/Ni/AuGe, or Au/Pt/TiW(/Ti)/Ni/AuGe. In addition, the former layer of the “/” shown above is located apart from the active layer from an electrical point of view. Although the first electrode is electrically connected to the first compound semiconductor layer, the case in which the first electrode is formed on the first compound semiconductor layer or the case in which the first electrode is connected to the first compound semiconductor layer with an electrically conductive material layer or an electrically conductive substrate interposed therebetween is also included. The first electrode and the second electrode may be formed, for example, by various types of PVD methods, such as a vacuum deposition method and a sputtering method. In order to electrically connect an external electrode or a circuit to the first electrode and/or the second electrode, a pad electrode may also be provided. The pad electrode preferably has a single layer structure or a multilayer structure, each containing at least one type of metal selected from the group consisting of titanium (Ti), aluminum (Al), platinum (Pt), gold (Au), and nickel (Ni). Alternatively, the pad electrode may also be formed to have a multilayer structure, such as a Ti/Pt/Au multilayer structure or a Ti/Au multilayer structure.
Example 1 relates to the semiconductor light emitting element according to the first and the third embodiments of the present disclosure. A schematic arrangement view of constituents of the semiconductor light emitting element of Example 1 is shown in
The semiconductor light emitting element (in particular, a semiconductor laser element) of Example 1 will be described with reference to the semiconductor light emitting element according to the first embodiment of the present disclosure. First regions 21 and second regions 22 are periodically and alternately arranged in an optical waveguide (in particular, a ridge portion 20) along an extending direction thereof, and when the number of the first regions 21 and the number of the second regions 22 are represented by P1 and P2, respectively, if (P1−P2)=1, P2 is an integer of 2 or more, and if (P2−P1)=1, P1 is an integer of 2 or more. In addition, the effective refractive index neff-1 of the first region 21 is different from the effective refractive index neff-2 of the second region 22. In addition, the semiconductor light emitting element of Example 1 emits two types of light in a fundamental transverse mode (the semiconductor light emitting element of each of Examples 2 to 4 described later also has the same performance as described above). Alternatively, the semiconductor light emitting element of Example 1 will be described with reference to the semiconductor light emitting element according to the third embodiment of the present disclosure. First regions 21 and second regions 22 are periodically and alternately arranged in an optical waveguide (in particular, a ridge portion 20) along an extending direction thereof, and when the number of the first regions 21 and the number of the second regions 22 are represented by P1 and P2, respectively, if (P1−P2)=1, P2 is an integer of 2 or more, if (P2−P1)=1, P1 is an integer of 2 or more. In addition, the semiconductor light emitting element of Example 1 emits two types of light in a fundamental transverse mode. In this case, in particular, the value of P1 is “4”, and the value of P2 is “3”. In Examples 2 to 4 which will be described later, as is the case described above, P1 is set to 4, and P2 is set to 3. In addition, the effective refractive index neff-1 of the first region 21 is determined by an active layer, a clad layer, a ridge depth, and an oscillation wavelength. On the other hand, ZnO is diffused to a position in the vicinity of the side of the ridge portion 20 to disorder the active layer, so that the refractive index of the second region 22 is decreased. Hence, the effective refractive index neff-2 of the second region 22 is decreased lower than that of the first region 21. The decrease in refractive index caused by this disordering is determined by a diffusion depth, and this diffusion depth can be controlled by a diffusion temperature and a diffusion time.
Furthermore, in the semiconductor light emitting element of Example 1, when the length of the first region 21 along the extending direction of the optical waveguide (ridge portion 20) is represented by L1, and the average wavelength of light to be emitted is represented by λave, the following equation is satisfied.
0.7×{λave/(neff-1−neff-2)}≦L1≦1.3×{λave/(neff-1−neff-2)}
In particular, L1=λave/(neff-1−neff-2) holds. Alternatively, the following equation is satisfied.
1×10−3≦(neff-1−neff-2)/neff-1≦1×10−2
In addition, when the total length of the first regions 21 along the extending direction of the optical waveguide (ridge portion 20) and the total length of the second regions 22 along the extending direction of the optical waveguide (ridge portion 20) are represented by L1 and L2, respectively, the following equation is satisfied.
0.1≦L2/(L1+L2)≦0.4
Furthermore, when the maximum peak value of the wavelength of light to be emitted from the semiconductor light emitting element and the wavelength width of the light are represented by λmax and Δλ, respectively, the following equation is satisfied.
Δλ/λmax≧1.5×10−4
In more particular, in the semiconductor light emitting element of Example 1, the total length of the ridge portion 20 is 1.00 mm, and the width of the ridge portion 20 is 1.8 μm. In addition, the other physical values are as shown below.
neff-1=3.2700
neff-2=3.2655
λave=648.75 nm
λmax=650.0 nm (=λ1)
λ2=647.5 nm
Δλ=2.5 nm
Although an anti-reflection (AR) coating layer or a low reflection coating layer is formed on a light emission surface 25, and a high reflection (HR) coating layer is formed on a light reflection surface 26, those coating layers are omitted in the drawings.
In Example 1, one ridge portion 20 is occupied with the first regions 21 and the second regions 22. In addition, in the vicinity of the second region 22, a refractive index control region (a refractive index change region, a refractive index disturbance region, a disorder region, or a waveguide loss decrease region) 23 is formed which makes the effective refractive index neff-2 of the second region 22 different from the effective refractive index neff-1 of the first region 21. The refractive index control region 23 is formed 2 μm apart from one side of the ridge portion 20. The length of the refractive index control region 23 along the extending direction of the optical waveguide (ridge portion 20) is 90 μm, and the width of the refractive index control region 23 is 20 μm. In Example 1, in the refractive index control region 23, a substance decreasing the refractive index (substance/impurity increasing the bandgap in the refractive index control region 23), in particular, zinc oxide (ZnO), is contained.
In Example 1, as a substrate 10, an n-GaAs substrate is used. In addition, the semiconductor light emitting element of Example 1 emits red light. In this case, an active layer 33 is provided for the optical waveguide (ridge portion 20), and the active layer 33 is formed of an AlGaInP-based compound semiconductor. In addition, the active layer 33 has a quantum well structure in which at least one well layer formed of a GaInP layer or an AlGaInP layer and at least two barrier layers each formed of an AlGaInP layer are laminated to each other. The structure of a compound semiconductor-laminate structure 30 formed of a GaPInP-based compound semiconductor of the semiconductor light emitting element of Example 1 is shown in the following Table 1, and the compound semiconductor layer described in the lowermost column is formed on the substrate 10. The active layer 33 has a multiquantum well structure, and in particular, the barrier layer is configured to include four layers, and the well layer is configured to include three layers. The structure described above is the same as that in Examples 2 to 4 which will be described later.
Hereinafter, with reference to
First, on the substrate 10, the compound semiconductor-laminate structure 30 including the active layer 33 is formed. In particular, although various types of compound semiconductor layers are crystal-grown by an MOCVD method, in this case, for example, phosphine (PH3) may be used as a phosphorous raw material, a trimethyl gallium (TMG) gas or a triethyl gallium (TEG) gas may be used as a gallium raw material, a trimethyl aluminum (TMA) gas may be used as an aluminum raw material, a trimethyl indium (TMI) gas may be used as an In raw material, a monosilane gas (SiH4 gas) may be used as a silicon raw material, and a cyclopentadienyl magnesium gas may be used as a Mg source. In more particular, on a principal surface of the substrate 10 formed of an n-GaAs substrate, the buffer layer 10′, the first compound semiconductor layer 31, the active layer 33, and the second compound semiconductor layer 32 are epitaxial-grown by a general MOCVD method, that is, by a MOCVD method using an organic metal and/or a hydrogen compound as a raw material gas. Accordingly, the structure shown in a schematic partial cross-sectional view of
Subsequently, based on common photolithographic and etching techniques, the compound semiconductor-laminate structure 30 is partially etched, so that a ridge portion 20 having a predetermined width is formed. In particular, a predetermined portion of the second compound semiconductor layer 32 is etched in a thickness direction thereof, so that the part of the second compound semiconductor layer 32 in the thickness direction is removed. Accordingly, the ridge portion 20 can be formed as shown in
Next, in order to make the effective refractive index neff-2 of the second region 22 different from the effective refractive index neff-1 of the first region 21, the refractive index control region 23 is provided in the vicinity of the second region 22. In particular, by a lift-off method, a ZnO layer 23′ is formed on an exposed portion of the second compound semiconductor layer 32 located in the vicinity of the second region 22 (see
Next, an insulating layer 36 of SiO2, SiN, or Al2O2 is formed (film formation) on the entire surface by a CVD method. In addition, the insulating layer 36 on the top surface of the second compound semiconductor layer 32 is removed by photolithographic and etching techniques, and by a lift-off method, a second electrode 35 is formed from the exposed top surface of the second compound semiconductor layer 32 onto the insulating layer 36. In addition, by a common method, a first electrode 34 is formed on the rear surface of the substrate 10. Accordingly, the semiconductor light emitting element of Example 1 can be obtained (see
The results of the emission angle distribution and the wavelength spectrum obtained when the semiconductor light emitting element of Example 1 is continuously driven are shown in
In the semiconductor light emitting element of Example 1 or Example 2 which will be described later, the first regions 21 and the second regions 22 are periodically and alternately arranged, the effective refractive index neff-1 of the first region 21 is different from the effective refractive index neff-2 of the second region 22 (in particular, neff-1>neff-2 in Example 1), and in the first regions 21 and the second regions 22, the two types of laser light in a fundamental transverse mode are generated (oscillated). In this case, since (P1−P2)=1, and the value of P2 is an integer of 2 or more, laser light in a fundamental transverse mode generated in one second region 22 reaches an adjacent second region 22 before coupling with laser light in a fundamental transverse mode generated in the first region 21 is completed. As a result, the two types of laser light in a fundamental transverse mode (light having a wavelength λ1 and light having a wavelength λ2) are present. In addition, as a result, as the total light emitted from the semiconductor light emitting element, the value of the oscillation wavelength width Δλ can be increased, and without using a complicated element structure and/or circuit, the reduction in speckle noise can be achieved by the semiconductor light emitting element itself. In addition, since the optical intensity distribution of laser light to be emitted is the normal distribution as described above, a highly fine image can be obtained.
Example 2 is a modification of Example 1. As shown in
neff-1=3.2700
neff-2=3.2666
Example 3 is also a modification of Example 1. In Example 3, a predetermined drive current is allowed to pass through the first regions 21 and the second regions 22 of the optical waveguide, and in addition, a high frequency signal (such as 100 to 300 MHz, and in particular, 200 MHz in Example 3) is superimposed on the current. Accordingly, since the fluctuation in gain is generated, as shown in
Example 4 relates to the semiconductor light emitting element according to the second and the third embodiments of the present disclosure. A schematic arrangement view of constituents of the semiconductor light emitting element of Example 4 is shown in
The semiconductor light emitting element of Example 4 will be described with reference to the semiconductor light emitting element according to the second embodiment of the present disclosure. First regions 21 and second regions 22 are periodically and alternately arranged in an optical waveguide (ridge portion 20) along an extending direction thereof, and when the number of the first regions and the number of the second regions are represented by P1 and P2, respectively, if (P1−P2)=1 holds, P2 is an integer of 2 or more, and if (P2−P1)=1 holds, P1 is an integer of 2 or more. In addition, a width W1 of the first region 21 is different from a width W2 of the second region 22. In particular, in Example 4, W1<W2 holds. Alternatively, the semiconductor light emitting element of Example 4 will be described with reference to the semiconductor light emitting element according to the third embodiment of the present disclosure. First regions 21 and second regions 22 are periodically and alternately arranged in an optical waveguide (ridge portion 20) along an extending direction thereof, and when the number of the first regions and the number of the second regions are represented by P1 and P2, respectively, if (P1−P2)=1 holds, P2 is an integer of 2 or more, and if (P2−P1)=1 holds, P1 is an integer of 2 or more. In addition, two types of light in a fundamental transverse mode are emitted. In this case, in the semiconductor light emitting element of Example 4, one ridge portion 20 is also occupied with the first regions 21 and the second regions 22. In addition, when the width of the first region 21 and the width of the second region 22 are represented by W1 and W2, respectively, the following equation is satisfied.
1.2≦W2/W1≦2.5
Except that the [Step-120] is not performed and that the shape of the ridge portion 20 is different from that formed in the [Step-110], the semiconductor light emitting element of Example 4 can be formed by a method similar to that for the semiconductor light emitting element of Example 1, and hence, detailed description is omitted.
In the semiconductor light emitting element of Example 4, since the widths of the first region 21 and the second regions 22, which are periodically and alternately arranged, are different from each other (in particular, in Example 4, W1<W2), a wavelength λ2 of light in a fundamental transverse mode generated (oscillated) in the second region 22 is different from a wavelength λ1 of light in a fundamental transverse mode generated (oscillated) in the first region 21, and in addition, two types of light in a fundamental transverse mode are generated in the first region 21 and the second region 22. In this case, since (P1−P2)=2 holds, and the value of P2 is an integer of 2 or more, light in a fundamental transverse mode generated in one second region 22 reaches an adjacent second region 22 before coupling with light in a fundamental transverse mode generated in the first region 21 is completed. As a result, the two types of light in a fundamental transverse mode (light having a wavelength λ1 and light having a wavelength λ2) are present. In addition, as a result, as the total light emitted from the semiconductor light emitting element, the value of the oscillation wavelength width Δλ can be increased, and without using a complicated element structure and/or circuit, the reduction in speckle noise can be achieved by the semiconductor light emitting element itself. In addition, according to the result of measurement, it is confirmed that the optical intensity distribution of total light to be emitted is the normal distribution, and hence, a highly fine image can be obtained.
In addition, the configuration and the structure of the semiconductor light emitting element of Example 4 may be used in combination with the configurations and the structures of the semiconductor light emitting elements described in Examples 1 to 3.
Example 5 relates to the display device according to the fourth embodiment of the present disclosure. In Example 5, as shown in a conceptual view of
Alternatively, a plurality of grating light valve (GLV) elements each functioning as a one-dimensional modulation element may be used in combination with a polygon mirror or a galvano scanner. That is, as shown in a conceptual view of
Heretofore, although the present disclosure has been described with reference to the preferable examples, the present disclosure is not limited to the examples described above. The configurations and the structures of the semiconductor light emitting elements and the display device and the methods for manufacturing a semiconductor light emitting element of the examples have been described by way of example and may be appropriately changed and modified. For example, the wavelength λ1 of light in a fundamental transverse mode to be generated in the first region, the wavelength λ2 of light in a fundamental transverse mode to be generated in the second region, the average wavelength λave of light to be emitted, the maximum peak value λmax of the wavelength of light to be emitted, and the wavelength width Δλ of light to be emitted may be determined based on the specifications necessary for the semiconductor light emitting element, and for example, the length L1 of the first region along the extending direction of the optical waveguide, the length L2 of the second region along the extending direction of the optical waveguide, the width W1 of the first region, the width W2 of the second region, the effective refractive index neff-1 of the first region, the effective refractive index neff-2 of the second region, the size of the refractive index control region, and the position at which the refractive index control region is provided may be appropriately determined based on the specifications necessary for the semiconductor light emitting element by performing various types of evaluation tests. Even when the active layer is formed from a GaInN-based compound semiconductor instead of using a GaInP-based compound semiconductor, the same results as described above can also be obtained.
In addition, in the semiconductor light emitting element according to an embodiment of the present disclosure, third regions may be further provided, and three types of light (light having a wavelength λ1, light having a wavelength λ2, and light having a wavelength λ3) in a fundamental transverse mode may be allowed to be present. In particular, for example, a semiconductor light emitting element having an arrangement including the first region, the second region, the first region, the second region, the first region, the third region, the first region, the third region, and the first region in this order may be mentioned. In the examples, although the configuration including the first region, the second region, the first region, the second region, the first region, the second region, and the first region in this order has been described by way of example, for example, the configuration including the second region, the first region, the second region, the first region, the second region, the first region, and the second region in this order may also be used.
In the examples, although the semiconductor light emitting element is formed of a semiconductor laser element, from the compound semiconductor-laminate structure 30 (see Table 1) described in Example 1, a super luminescent diode (SLD) may also be formed. Although having an optical waveguide structure similar to that of the semiconductor laser element described in Example 1, the SLD has no oscillator structure unlike the semiconductor laser element. In the SLD, spontaneous emission light generated by current injection is amplified by stimulated emission while guided through an optical waveguide structure and is then emitted. The SLD as described above can be obtained when the optical reflectance at a light emission surface is set to be a very low value, and when the optical reflectance at a light reflection surface is set to be a very high value.
In addition, according to an embodiment of the present disclosure, the following structures may also be formed.
A semiconductor light emitting element in which first regions and second regions are periodically and alternately arranged in an optical waveguide along an extending direction thereof; when the number of the first regions and the number of the second regions are represented by P1 and P2, respectively, if (P1−P2)=1, P2 is an integer of 2 or more, and if (P2−P1)=1, P1 is an integer of 2 or more; and the effective refractive index of the first region is different from the effective refractive index of the second region.
0.7×{λave/(neff-1−neff-2)}≦L1≦1.3×{λave/(neff-1−neff-2)}
0.1≦L2/(L1+L2)≦0.4
1×10−3≦(neff-1−neff-2)/neff-1≦1×10−2
Δλ/λmax≧1.5×10−4
A semiconductor light emitting element in which first regions and second regions are periodically and alternately arranged in an optical waveguide along an extending direction thereof; when the number of the first regions and the number of the second regions are represented by P1 and P2, respectively, if (P1−P2)=1, P2 is an integer of 2 or more, and if (P2−P1)=1, P1 is an integer of 2 or more; and the width of the first region is different from the width of the second region.
1.2≦W2/W1≦2.5
0.1≦L2/(L1+L2)≦0.4
Δλ/λmax≧1.5×10−4
[19] The semiconductor light emitting element described in the above [18] in which when the length of the first region along the extending direction of the optical waveguide is represented by L1, the average wavelength of light to be emitted is represented by λave, the effective refractive index of the first region is represented by neff-1, and the effective refractive index of the second region is represented by neff-2, the following equation is satisfied.
0.7×{λave/(neff-1−neff-2)}≦L1≦1.3×{λave/(neff-1−neff-2)}
1×10−3≦(neff-1−neff-2)/neff-1≦1×10−2
A semiconductor light emitting element in which first regions and second regions are periodically and alternately arranged in an optical waveguide along an extending direction thereof; when the number of the first regions and the number of the second regions are represented by P1 and P2, respectively, if (P1−P2)=1, P2 is an integer of 2 or more, and if (P2−P1)=1, P1 is an integer of 2 or more; and two types of light in a fundamental transverse mode are emitted.
0.1≦L2/(L1+L2)≦0.4
Δλ/λmax≧1.5×10−4
A display device including the semiconductor light emitting element described in one of the above [1] to [35].
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 |
|---|---|---|---|
| 2013-034821 | Feb 2013 | JP | national |
