Patent Application
20130070801
1. Field of the Invention
The present invention relates to a semiconductor laser device and a method of manufacturing the same, and more particularly, it relates to a semiconductor laser device including a semiconductor element layer having a light emitting layer and a method of manufacturing the same.
2. Description of the Background Art
In general, a semiconductor laser is widely employed as the light source of an optical disk system or an optical communication system. Following improvement in performance of apparatuses constituting the system, characteristic improvement of the semiconductor laser is demanded. In particular, wavelength shortening and higher output of a laser beam are desired as the light source of a high-density optical disk system, and a blue-violet semiconductor laser having a lasing wavelength of about 405 nm has recently been developed with a nitride-based semiconductor, while higher output thereof is examined.
A semiconductor laser device allowing higher output by subjecting cavity facets of the laser device to facet coating treatment is proposed in general. Such a semiconductor laser device is disclosed in Japanese Patent Laying-Open No. 2007-201373, for example.
The aforementioned Japanese Patent Laying-Open No. 2007-201373 discloses a semiconductor laser device in which a first dielectric film made of an oxide film and a second dielectric film made of a nitride film or an oxynitride film are stacked in this order on a cavity facet on a light-emitting side. In the semiconductor laser device described in Japanese Patent Laying-Open No. 2007-201373, adhesiveness between the first dielectric film and the second dielectric film is improved by forming the second dielectric film similar in thermal expansion coefficient to the first dielectric film on the outer side of the first dielectric film, and heat radiability of the semiconductor laser device is improved by the second dielectric film made of the oxynitride film containing nitrogen, and hence higher output of the laser beam can be achieved. In this semiconductor laser device, attempt to employ the nitride film having higher thermal conductivity than the oxide film for the first dielectric film has been made in order to further improve the heat radiability of the dielectric multilayer film.
In the semiconductor laser device disclosed in the aforementioned Japanese Patent Laying-Open No. 2007-201373, the second dielectric film similar in thermal expansion coefficient to the first dielectric film is formed on the outer side of the first dielectric film, whereby adhesiveness between the dielectric films are conceivably improved to some extent. In the semiconductor laser device for which higher output is demanded, on the other hand, the dielectric films tend to separate due to heat generation or heat absorption in the cavity facet, and hence improvement in the adhesiveness between the dielectric films is further demanded.
A semiconductor laser device according to a first aspect of the present invention comprises a semiconductor element layer having a light emitting layer, a first cavity facet formed on an end of the semiconductor element layer on a light-emitting side of a region including the light emitting layer, a first insulating film, made of AlN, formed on a surface of the first cavity facet a second insulating film, made of AlOXNY (0≦X<1.5, 0≦Y≦1), formed on a surface on an opposite side of the first insulating film to the first cavity facet, wherein a first interface between the first insulating film and the second insulating film has a first recess portion and a first projection portion.
In the present invention, the first cavity facet formed on the end on the light-emitting side is distinguished by the large-small relation between the intensity levels of laser beams emitted from a pair of cavity facets formed on the ends of the semiconductor laser device. In other words, the side on which the emission intensity of the laser beam is relatively large is the first cavity facet on the light-emitting side, while the side on which the emission intensity of the laser beam is relatively small is a second cavity facet on a light-reflecting side. In the present invention, as to combination of an oxygen composition ratio (X) and a nitrogen composition ratio (Y) constituting AlOXNY of the second insulating film, for example, when Y approaches zero without limit, X approaches 1.5 without limit. In this case, the mechanical property of the second insulating film (AlOXNY film) approaches the Al2O3 film without limit, and hence the range of the oxygen composition ratio (X) is specified as 0≦X≦1.5.
As hereinabove described, the semiconductor laser device according to the first aspect of the present invention comprises the first insulating film, made of AlN, formed on the surface of the first cavity facet and the second insulating film made of AlOXNY, and the first interface between the first insulating film and the second insulating film has roughness, whereby the first insulating film and the second insulating film are in contact with each other on the first interface having the roughness, and hence the first insulating film and the second insulating film can be in contact with each other through a wider surface area due to formation of the roughness as compared with a case where the first insulating film and the second insulating film are in contact with each other on an flat contact interface with no roughness. Thus, adhesiveness between the dielectric films can be further improved.
The semiconductor laser device comprises the first insulating film, made of AlN, formed on the surface of the first cavity facet and the second insulating film made of AlOXNY film, whereby reflectance for the laser beam emitted from the first cavity facet can be easily controlled by adjusting the thickness of the second insulating film. Thus, the semiconductor laser device allowing higher output can be easily formed.
In the aforementioned semiconductor laser device according to the first aspect, a maximum value H1 of a height from a bottom portion of the first recess portion to a top portion of the first projection portion adjacent to the first recess portion on the first interface is preferably set to H1 <λ/n1 and H1<λ/n2 when a wavelength of a laser beam emitted by the light emitting layer is λ and average refractive indices of the first insulating film and the second insulating film are n1 and n2, respectively. According to this structure, the size of the pluralities of projecting and recess portions on the first interface (height of undulation) is smaller than λ/n1 and λ/n2. Thus, the laser beam emitted from the first cavity facet is transmitted through the interface without being influenced by the state of the roughness and then transmitted through the second insulating film. Consequently, the reflectance control function of the second insulating film set to have a desirable reflectance can be easily inhibited from being influenced by the roughness of the first interface.
According to the aforementioned structure, the reflectance for the laser beam on the interface between AlN and AlOXNY is reduced, and hence the laser beam can be effectively emitted from the first cavity facet.
In the aforementioned semiconductor laser device according to the first aspect, the AlOXNY preferably satisfies X<Y. According to this structure, the second insulating film can be formed on the first insulating film in the state where the interface between the second insulating film and the first insulating film has the roughness, when the cavity facet is subjected to the facet coating treatment. Consequently, the second insulating film can be formed in a state where adhesiveness with the first insulating film is excellent. According to the aforementioned structure, the quantity of diffusion of oxygen contained in the second insulating film to the first insulating film can be suppressed. Thus, diffusion of oxygen from the first insulating film to the semiconductor element layer is suppressed, and hence catastrophic optical damage (COD) on the first cavity facet can be suppressed.
In the aforementioned semiconductor laser device according to the first aspect, a thickness of the first insulating film is preferably smaller than that of the second insulating film. According to this structure, the thickness of the first insulating film made of the nitride film is smaller than that of the second insulating film made of the oxynitride film, and hence stress of the first insulating film (nitride film) in contact with the first cavity facet can be kept small. Thus, separation of the first insulating film from the first cavity facet or separation of the second insulating film from the first insulating film can be suppressed.
The aforementioned semiconductor laser device according to the first aspect preferably further comprises a third insulating film, made of either an oxide film or a nitride film, formed on a surface on an opposite side of the second insulating film to the first cavity facet. According to this structure, the reflectance for the laser beam emitted from the first cavity facet can be easily controlled by adjusting the thickness of the third insulating film. Thus, the semiconductor laser device allowing higher output can be easily formed.
In the aforementioned structure in which the semiconductor laser device further comprises the third insulating film, the second insulating film and the third insulating film preferably contain the same metal element. According to this structure, the second insulating film and the third insulating film which are in contact with each other are materials containing the same kind of metal element, and hence adhesiveness when the second insulating film and the third insulating film are in contact with each other can be improved.
In this case, the second insulating film and the third insulating film preferably each contain Al. According to this structure, the insulating properties of the second insulating film and the third insulating film can be improved since a nitride and an oxide containing Al each have an excellent insulating property. When the nitride film containing Al is employed, incorporation of oxygen into the first insulating film and the semiconductor element layer can be effectively suppressed.
The aforementioned semiconductor laser device according to the first aspect preferably further comprises a second cavity facet formed on an end of the semiconductor element layer on a light-reflecting side of a region including the light emitting layer, a fourth insulating film, made of AlN, formed on a surface of the second cavity facet, and a fifth insulating film, made of AlOXNY (0≦X<1.5, 0<Y≦1), formed on a surface on an opposite side of the fourth insulating film to the second cavity facet, wherein a second interface between the fourth insulating film and the fifth insulating film has a second recess portion and a second projection portion. According to this structure, the fourth insulating film and the fifth insulating film are in contact with each other on the second interface having the roughness, and hence the fourth insulating film and the fifth insulating film can be in contact with each other through a wider surface area due to formation of the roughness as compared with a case where the fourth insulating film and the fifth insulating film are in contact with each other on an flat contact interface with no roughness. Thus, adhesiveness between the dielectric films can be further improved also on the second cavity facet. The semiconductor laser device comprises the fourth insulating film, made of AlN, formed on the surface of the second cavity facet film and the fifth insulating film, made of AlOXNY, whereby reflectance for the laser beam emitted from the second cavity facet can be easily controlled by adjusting the thickness of the fifth insulating film. Thus, the semiconductor laser device allowing higher output can be easily formed.
In the aforementioned structure in which the semiconductor laser device further comprises the second cavity facet, a maximum value H2 of a height from a bottom portion of the second recess portion to a top portion of the second projection portion adjacent to the second recess portion on the second interface is set to H2<λ/n3 and H2<λ/n4 when a wavelength of a laser beam emitted by the light emitting layer is λ and average refractive indices of the fourth insulating film and the fifth insulating film are n3 and n4, respectively. According to this structure, the size of the pluralities of projecting and recess portions on the second interface (height of undulation) is smaller than λ/n3 and λ/n4. Thus, the laser beam emitted from the second cavity facet can be transmitted through the interface without being influenced by the state of the roughness and then transmitted through the fifth insulating film. Consequently, the reflectance control function of the fifth insulating film set to have a desirable reflectance can be easily inhibited from being influenced by the roughness of the second interface.
In the aforementioned structure in which the semiconductor laser device further comprises the second cavity facet, the AlOXNY preferably satisfies X<Y. According to this structure, the fifth insulating film can be formed on the fourth insulating film in the state where the interface between the fifth insulating film and the fourth insulating film has the roughness, when the second cavity facet is subjected to the facet coating treatment. Consequently, the fifth insulating film can be formed in a state where adhesiveness with the fourth insulating film is excellent. According to the aforementioned structure, the quantity of diffusion of oxygen contained in the fifth insulating film to the fourth insulating film can be suppressed. Thus, diffusion of oxygen from the fourth insulating film to the semiconductor element layer is suppressed, and hence COD on the second cavity facet can be suppressed.
In the aforementioned structure in which the semiconductor laser device further comprises the second cavity facet, a thickness of the fourth insulating film is preferably smaller than that of the fifth insulating film. According to this structure, the thickness of the fourth insulating film made of the nitride film is smaller than that of the fifth insulating film made of the oxynitride film, and hence stress of the fourth insulating film (nitride film) in contact with the second cavity facet can be kept small. Thus, separation of the fourth insulating film from the second cavity or separation of the fifth insulating film from the fourth insulating film can be suppressed.
In the aforementioned structure in which the semiconductor laser device further comprises the second cavity facet, the semiconductor laser device preferably further comprises a sixth insulating film, including at least any of an oxide film, a nitride film and an oxynitride film, formed on a surface on an opposite side of the fifth insulating film to the second cavity facet. According to this structure, the reflectance for the laser beam emitted from the second cavity facet can be easily controlled by adjusting the thickness of the sixth insulating film. Thus, the semiconductor laser device allowing higher output can be more easily formed.
In the aforementioned structure in which the semiconductor laser device further comprises the sixth insulating film, the fifth insulating film and the sixth insulating film preferably contain the same metal element. According to this structure, the fifth insulating film and the sixth insulating film which are in contact with each other are materials containing the same kind of metal element, and hence adhesiveness when the fifth insulating film and the sixth insulating film are in contact with each other can be improved.
In this case, the fifth insulating film and the sixth insulating film preferably each contain Al. According to this structure, the insulating properties of the fifth insulating film and the sixth insulating film can be improved since a nitride and an oxide containing Al each have an excellent insulating property. When the nitride film containing Al is employed, incorporation of oxygen into the fourth insulating film and the semiconductor element layer can be effectively suppressed.
In the aforementioned structure in which the semiconductor laser device further comprises the sixth insulating film, the semiconductor laser device preferably further comprises a seventh insulating film, made of a multilayer reflecting film, formed on a surface on an opposite side of the sixth insulating film to the second cavity facet. According to this structure, reflectance for the laser beam emitted from the second cavity facet on the light-reflecting side can be easily controlled by adjusting the thickness of the seventh insulating film.
A method of manufacturing a semiconductor laser device according to a second aspect of the present invention comprises steps of forming a semiconductor element layer having a light emitting layer, forming cavity facets on ends of the semiconductor element layer on a region including the light emitting layer, and forming a first insulating film made of AlN and a second insulating film made of AlOXNY (0≦X<1.5, 0<Y≦1) from the cavity facet side on a surface of the facet on the light-emitting side in the cavity facets so that an interface between the first insulating film and the second insulating film has a first recess portion and a first projection portion.
As hereinabove described, the method of manufacturing a semiconductor laser device according to the second aspect of the present invention comprises the step of forming the first insulating film made of AlN and the second insulating film made of AlOXNY from the surface side of the cavity facet on the surface of the facet on the light-emitting side so that the interface between the first insulating film and the second insulating film has the roughness, whereby the first insulating film and the second insulating film are in contact with each other on the interface having the roughness, and hence the first insulating film and the second insulating film can be in contact with each other through a wider surface area due to formation of the roughness as compared with a case where the first insulating film and the second insulating film are in contact with each other on an flat contact interface with no roughness. Thus, adhesiveness between the dielectric films can be further improved.
In the aforementioned method of manufacturing the semiconductor laser device according to the second aspect, the step of forming the first insulating film and the second insulating film preferably includes a step of forming the first insulating film and the second insulating film by ECR plasma. According to this structure, the first insulating film and the second insulating film can be formed so that the interface between the first insulating film and the second insulating film easily has the roughness.
In the aforementioned structure including the step of forming the first insulating film and the second insulating film by ECR plasma, the step of forming the first insulating film and the second insulating film preferably includes a step of forming the first insulating film on the surface of the cavity facet in a state where ECR plasma is generated in an N2 gas atmosphere, and a step of forming the second insulating film on a surface of the first insulating film formed with the first recess portion and the first projection portion while forming the first recess portion and the first projection portion on the surface of the first insulating film by forming the second insulating film on the surface of the first insulating film in a state where ECR plasma is generated in an atmosphere N2 and O2 gas. According to this structure, the second insulating film covering this roughness can be easily stacked while forming the roughness on the surface of the first insulating film when forming the second insulating film.
In this case, the second insulating film is preferably formed on the surface of the first insulating film in a state where the ECR plasma is generated by applying high-frequency power when forming the second insulating film on the surface of the first insulating film. According to this structure, the roughness for adhering the second insulating film to the surface of the first insulating film can be easily formed.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.
Embodiments of the present invention will be hereinafter described with reference to the drawings.
A structure of a nitride-based semiconductor laser device 100 according to a first embodiment of the present invention will be now described with reference to
In the nitride-based semiconductor laser device 100 according to the first embodiment of the present invention, a semiconductor element layer 20 having a lasing wavelength of about 405 nm is formed on a surface of an oxygen-doped n-type (0001) plane GaN substrate 10 having a thickness of about 100 μm and having a carrier concentration of about 5×1018 cm−3, as shown in
In the nitride-based semiconductor laser device 100, a light emitting surface 1 and a light reflecting surface 2 are formed on respective both end portions in a cavity direction (direction A), as shown in
According to the first embodiment, the dielectric multilayer film 40 in which an AlN film 41 having a thickness of about 10 nm in contact with the light emitting surface 1 and an AlOXNY film 42 having a thickness of about 30 nm in contact with the AlN film 41 are formed successively from a side closer to the light emitting surface 1 is formed on the light emitting surface 1 of the nitride-based semiconductor laser device 100, as shown in
According to the first embodiment, when an interface 3 on which the AlN film 41 and the AlOXNY film 42 are in contact with each other is microscopically viewed, the interface 3 has roughness by a plurality of recess portions 3a and a plurality of projecting portions 3b as viewed from the AlOXNY film 42 side, as shown in
This roughness is formed to have planar spread along a width direction (direction B in
A maximum value H1 (see
The semiconductor element layer 20 having a lasing wavelength λ of about 405 nm is preferably so formed that the maximum value H1 of the height from the bottom portion of each recess portion 3a to the top portion of the projecting portion 3b forming the interface 3 is H1<about 193 nm.
According to the first embodiment, the AlOXNY film 42 is so formed that a nitrogen composition ratio (Y) is higher than an oxygen composition ratio (X) (X<Y). Thus, the interface 3 between the AlN film 41 and the AlOXNY film 42 is formed to easily have the roughness.
As shown in
In the semiconductor element layer 20, an n-type layer 21, made of Ge-doped n-type GaN having a doping quantity of about 5×1018 cm−3, having a thickness of about 100 nm is formed on the n-type (0001) plane GaN substrate 10, as shown in
An n-type carrier blocking layer 23, made of Ge-doped n-type Al0.16Ga0.84N having a doping quantity of about 5×1018 cm−3 and a carrier concentration of about 5×1018 cm−3, having a thickness of about 5 nm is formed on the n-type cladding layer 22. An n-side optical guide layer 24, made of undoped GaN, having a thickness of about 100 nm is formed on the n-type carrier blocking layer 23. An active layer 25 is formed on the n-side optical guide layer 24. This active layer 25 has an MQW structure in which four barrier layers made of undoped In0.02Ga0.98N each having a thickness of about 20 nm and three well layers made of undoped In0.1Ga0.9N each having a thickness of about 3 nm are alternately stacked.
As shown in
A p-type cladding layer 28, made of p-type Al0.07Ga0.93N doped with Mg having a doping quantity of about 4×1019 cm−3 and a carrier concentration of about 5×1017 cm−3, having a projecting portion 28a and planar portions 28b other than the projecting portion 28a is formed on the cap layer 27. The planar portions 28b of the p-type cladding layer 28 each have a thickness of about 80 nm on both sides of the projecting portion 28a. A height from the planar portions 28b of the p-type cladding layer 28 to the projecting portion 28a is about 320 nm and a width of the projecting portion 28a is about 1.5 μm.
A p-side contact layer 29, made of undoped In0.02Ga0.98N, having a thickness of about 10 nm is formed on the projecting portion 28a of the p-type cladding layer 28. A ridge 30 is formed by the p-side contact layer 29 and the projecting portion 28a of the p-type cladding layer 28. The ridge 30 has a width of about 1.5 μm on the lower portion and is formed to extend in a [1-100] direction (direction A in
As shown in
As shown in
A manufacturing process for the nitride-based semiconductor laser device 100 according to the first embodiment will be now described with reference to
As shown in
A method of forming the cavity facets constituting the nitride-based semiconductor laser device 100 (see
First, dotted scribed lines are formed on prescribed portions, except the ridge 30, of a wafer formed with the aforementioned semiconductor laser structure by laser scribing or mechanical scribing. Then, a pair of the cavity facets (the light emitting surface 1 and the light reflecting surface 2) are formed by cleaving the wafer along the scribed lines. Thereafter, the wafer in a bar state provided with the cavity facets is introduced into an electron cyclotron resonance (ECR) sputtering film forming apparatus.
Further, ECR plasma is applied to the light emitting surface 1 (see
According to the first embodiment, the AlN film 41 is first formed on the surface of the light emitting surface 1 by ECR plasma, as shown in
Thereafter, the Al2O3 film 51 is formed on the surface of the dielectric multilayer film 40 (see
Similarly to the aforementioned step of cleaning the light emitting surface 1, ECR plasma is applied to the light reflecting surface 2 (see
Finally, the wafer in the form of a bar is divided into device along the cavity direction, thereby forming a large number of the separated nitride-based semiconductor laser devices 100.
According to the first embodiment, as hereinabove described, the AlN film 41 and the AlOXNY film 42 are so formed in this order on the surface of the light emitting surface 1 that the interface 3 has the roughness, whereby the AlN film 41 and the AlOXNY film 42 are in contact with each other through the interface 3 having the roughness, and hence the AlN film 41 and the AlOXNY film 42 can be in contact with each other through a wider surface area due to formation of the roughness as compared with a case where the AlN film 41 and the AlOXNY film 42 are in contact with each other on an flat contact interface with no roughness. Thus, adhesiveness between the AlN film 41 and the AlOXNY film 42 can be further improved.
The AlN film 41 and the AlOXNY film 42 are formed on the surface of the light emitting surface 1, whereby a reflectance for the laser beam emitted from the light emitting surface 1 can be easily controlled by adjusting the thickness of the AlOXNY film 42. Thus, the nitride-based semiconductor laser device 100 allowing higher output can be easily formed.
According to the first embodiment, the plurality of projecting portions or recess portions which the AlOXNY film 42 has are fitted into the plurality of recess portions or projecting portions which the AlN film 41 on the interface 3, so that the roughness of the interface 3 is formed, whereby the AlN film 41 and the AlOXNY film 42 are stacked in contact with each other with no clearance through the pluralities of recess portions and projecting portions formed on the respective interface 3 sides, and hence adhesiveness between the AlN film 41 and the AlOXNY film 42 can be reliably obtained.
According to the first embodiment, the roughness of the interface 3 is formed by the pluralities of recess portions 3a and projecting portions 3b, and the maximum value H1 of the height from the bottom portion of each recess portion 3a to the top portion of the projecting portions 3b adjacent to the recess portion 3a on the interface 3 is set to H1<λ/n1 and H1<λ/n2 when the wavelength of the laser beam emitted by the active layer 25 is λ, and the average refractive indices of the AlN film 41 and the AlOXNY film 42 are n1 and n2, respectively, whereby the size of the pluralities of projecting and recess portions on the interface 3 (height from the bottom portion of each recess portion 3a to the top portion of the projecting portions 3b adjacent to the recess portion 3a) is smaller than λ/n1 and λ/n2. Thus, the laser beam emitted from the light emitting surface 1 is transmitted through the interface 3 without being influenced by the state of the roughness and then transmitted through the AlOXNY film 42. Consequently, the reflectance control function of the AlOXNY film 42 set to have a desirable reflectance can be easily inhibited from being influenced by the roughness of the interface 3.
According to the first embodiment, the interface 3 has the roughness which is set to H1<λ/n1 and H1<λ/n2 described later, whereby the reflectance for the laser beam on the interface 3 between the AlN film 41 and the AlOXNY film 42 is reduced, and hence the laser beam can be effectively emitted from the light emitting surface 1.
According to the first embodiment, the nitrogen composition ratio (Y) in the AlOXNY film 42 is higher than the oxygen composition ratio (X) (X<Y), whereby the AlOXNY film 42 can be formed on the surface of the AlN film 41 in the state where the interface 3 between the AlOXNY film 42 and the AlN film 41 has the roughness, when the light emitting surface 1 is subjected to facet coating treatment. Consequently, the AlOXNY film 42 can be formed in a state where adhesiveness with the AlN film 41 is excellent.
The nitrogen composition ratio of the AlOXNY film 42 is higher than the oxygen composition ratio, and hence the quantity of diffusion of oxygen contained in the AlOXNY film 42 to the AlN film 41 can be suppressed. Thus, diffusion of oxygen from the AlN film 41 to the semiconductor element layer 20 is suppressed, and hence COD on the light emitting surface 1 can be suppressed.
According to the first embodiment, the thickness (about 10 nm) of the AlN film 41 is smaller than the thickness (about 30 nm) of the AlOXNY film 42, whereby stress of the AlN film 41 (nitride film) in contact with the light emitting surface 1 can be kept small. Thus, separation of the AlN film 41 from the light emitting surface 1 or separation of the AlOXNY film 42 from the AlN film 41 can be suppressed.
According to the first embodiment, the Al2O3 film 51 formed on the surface of the AlOXNY film 42 on the side opposite to the light emitting surface 1 is provided, whereby the reflectance for the laser beam emitted from the light emitting surface 1 can be easily controlled by adjusting the thickness of the Al2O3 film 51. Thus, the nitride-based semiconductor laser device 100 allowing higher output can be easily formed.
According to the first embodiment, the AlOXNY film 42 and the Al2O3 film 51 contain the same Al element, whereby adhesiveness between the AlOXNY film 42 and the Al2O3 film 51 can be improved. The insulating properties of the AlOXNY film 42 and the Al2O3 film 51 can be improved, since a nitride and an oxide containing Al each have an excellent insulating property.
According to the first embodiment, the semiconductor element layer 20 including the active layer 25 is made of a nitride-based semiconductor. Thus, breakage of the cavity facet (light emitting surface 1) on the light-emitting side especially resulting from heat generation in laser beam emission can be effectively suppressed in the nitride-based semiconductor laser device 100 having a short lasing wavelength of about 405 nm and emitting a high-energy laser beam.
In the manufacturing process of the first embodiment, the AlOXNY film 42 is formed on the surface of the AlN film 41 by ECR plasma, whereby the interface 3 between the AlN film 41 and the AlOXNY film 42 can be easily formed to have the roughness.
In the manufacturing process of the first embodiment, the cleaved light emitting and reflecting surfaces 1 and 2 are cleaned by applying the ECR plasma, whereby the nitride-based semiconductor laser device 100 in which deterioration of the cavity facets in the vicinity of the optical waveguide or COD is suppressed by cleaning can be easily formed.
In the manufacturing process of the first embodiment, the AlN film 41 is formed on the surface of the light emitting surface 1 in the state of generating the ECR plasma in the N2 gas atmosphere and the flow ratio of N2 gas and O2 gas is thereafter adjusted, so that the AlOXNY film 42 is formed on the surface of the AlN film 41 formed with roughness while forming the roughness on the surface of the AlN film 41, whereby the AlOXNY film 42 covering this roughness can be easily stacked while roughness is formed on the surface of the AlN film 41 when forming the AlOXNY film 42.
In the manufacturing process of the first embodiment, the AlOXNY film 42 is formed on the surface of the AlN film 41 in the state of applying high-frequency power (RF power) to generate the ECR plasma, whereby the roughness for adhering the AlOXNY film 42 to the surface of the AlN film 41 can be easily formed.
A second embodiment will be described with reference to
According to the second embodiment, the dielectric multilayer film 70 in which an AlN film 71 having a thickness of about 10 nm in contact with the light reflecting surface 2 and an AlOXNY film 72 having a thickness of about 30 nm in contact with the AlN film 71 are formed successively from a side closer to the light reflecting surface 2 is formed on light reflecting surface 2 of a nitride-based semiconductor laser device 200, as shown in
According to the second embodiment, when an interface 4 on which the AlN film 71 and the AlOXNY film 72 are in contact with each other is microscopically viewed, the interface 4 has roughness by a plurality of recess portions 4a and a plurality of projecting portions 4b as viewed from the AlOXNY film 72 side, as shown in
This roughness is formed to have planar spread along a width direction (direction B in
A maximum value H2 (see
According to the second embodiment, the AlOXNY film 72 is so formed that a nitrogen composition ratio (Y) is higher than an oxygen composition ratio (X) (X<Y) in addition to the AlOXNY film 42. Thus, the interface 4 between the AlN film 71 and the AlOXNY film 72 is formed to easily have the roughness.
According to the second embodiment, a dielectric multilayer film 80 in which an Al2O3 film 81 having a thickness of about 60 nm in contact with the dielectric multilayer film 70, an SiO2 film 82 having a thickness of about 140 nm in contact with the Al2O3 film 81, and a multilayer reflecting film 83, in contact with the SiO2 film 82, having a thickness of about 720 nm, formed by alternately stacking six SiO2 films each having a thickness of about 70 nm as a low refractive index film and six ZrO2 films each having a thickness of about 50 nm as a high refractive index film are formed is formed on a surface of the dielectric multilayer film 70 on a side opposite to the light reflecting surface 2. The multilayer reflecting film 83 has a function of controlling a reflectance, and the light reflecting surface 2 side is set to have a high reflectance of about 98% for the laser beam due to the multilayer reflecting film 83. The Al2O3 film 81 and the SiO2 film 82 are each an example of the “sixth insulating film” in the present invention, and the multilayer reflecting film 83 is an example of the “seventh insulating film” in the present invention. The dielectric multilayer film 80 shown in
The remaining structure of the nitride-based semiconductor laser device 200 according to the second embodiment is similar to that of the aforementioned first embodiment. As to a manufacturing process for the nitride-based semiconductor laser device 200 according to the second embodiment, the AlN film 71 and the AlOXNY film 72 are stacked in this order on the surface of the light reflecting surface 2 through a manufacturing process similar to that of the aforementioned first embodiment, thereby forming the dielectric multilayer film 70. Thus, the interface 4 is formed to have the roughness.
According to the second embodiment, as hereinabove described, the AlN film 71 and the AlOXNY film 72 are so formed in this order on the surface of the light reflecting surface 2 that the interface 4 has the roughness, whereby the AlN film 71 and the AlOXNY film 72 are in contact with each other through the interface 4 having the roughness, and hence the AlN film 71 and the AlOXNY film 72 can be in contact with each other through a wider surface area due to formation of the roughness as compared with a case where the AlN film 71 and the AlOXNY film 72 are in contact with each other on an flat contact interface with no roughness. Thus, adhesiveness between the AlN film 71 and the AlOXNY film 72 can be further improved on the light reflecting surface 2, in addition to the light emitting surface 1.
According to the second embodiment, the maximum value H2 of the height from the bottom portion of each recess portion 4a to the top portion of the projecting portions 4b adjacent to the recess portion 4a on the interface 4 is set to H2<λ/n3 and H2<λ/n4, when the roughness of the interface 4 is formed by the pluralities of recess portions 4a and projecting portions 4b, and the average refractive indices of the AlN film 71 and the AlOXNY film 72 are n3 and n4, respectively, whereby the size of the pluralities of projecting and recess portions on the interface 4 (height from the bottom portion of each recess portion 4a to the top portion of the projecting portions 4b adjacent to the recess portion 4a) is smaller than λ/n3 and λ/n4. Thus, the laser beam emitted from the light reflecting surface 2 is transmitted through the interface 4 without being influenced by the state of the roughness and then transmitted through the AlOXNY film 72. Consequently, the reflectance control function of the multilayer reflecting film 83 set to have a desirable reflectance can be easily inhibited from being influenced by the roughness of the interface 4.
According to the second embodiment, the nitrogen composition ratio (Y) in the AlOXNY film 72 is higher than the oxygen composition ratio (X) (X<Y), whereby the AlOXNY film 72 can be formed on the surface of the AlN film 71 in the state where the interface 4 between the AlOXNY film 72 and the AlN film 71 has the roughness, when the light reflecting surface 2 is subjected to facet coating treatment. Consequently, the AlOXNY film 72 can be formed in a state where adhesiveness with the AlN film 71 is excellent.
According to the second embodiment, the thickness (about 10 nm) of the AlN film 71 is smaller than the thickness (about 30 nm) of the AlOXNY film 72, whereby stress of the AlN film 71 (nitride film) in contact with the light reflecting surface 2 can be kept small. Thus, separation of the AlN film 71 from the light reflecting surface 2 or separation of the AlOXNY film 72 from the AlN film 71 can be suppressed.
According to the second embodiment, the nitride-based semiconductor laser device 200 comprises the Al2O3 film 81 and the SiO2 film 82 formed on the surface of the AlOXNY film 72 on the side opposite to the light reflecting surface 2, whereby the reflectance for the laser beam emitted from the light reflecting surface 2 can be easily controlled by adjusting the respective thicknesses of the Al2O3 film 81 and the SiO2 film 82. Thus, the nitride-based semiconductor laser device 200 allowing higher output can be easily formed.
According to the second embodiment, the AlOXNY film 72, the Al2O3 film 81 and the SiO2film 82 contain the same Al element, whereby adhesiveness between the AlOXNY film 72 and the Al2O3film 81, and adhesiveness between the Al2O3 film 81 and the SiO2 film 82 can be improved. The insulating properties of the AlOXNY film 72 and the Al2O3 film 81 can be improved since an oxynitride and an oxide containing Al each have an excellent insulating property.
According to the second embodiment, the nitride-based semiconductor laser device 200 comprises the multilayer reflecting film 83, obtained by alternately stacking the six SiO2 films and the six ZrO2 films, formed on the surface of the SiO2film 82 on the side opposite to the light reflecting surface 2, whereby the reflectance for the laser beam emitted from the light reflecting surface 2 can be easily controlled by adjusting the thickness of the multilayer reflecting film 83.
The remaining effects of the second embodiment are similar to those of the aforementioned first embodiment.
A first modification of the second embodiment will be described with reference to
According to the first modification of the second embodiment, a dielectric multilayer film 270 in which an AlN film 71 having a thickness of about 10 nm and an AlOXNY film 272 having a thickness of about 60 nm are formed successively from a side closer to a light reflecting surface 2 is formed on the light reflecting surface 2 of a nitride-based semiconductor laser device 210, as shown in
Further, a dielectric multilayer film 280 in which an SiO2 film 82 having a thickness of about 140 nm and a multilayer reflecting film 83, having a thickness of about 720 nm, formed by alternately stacking six SiO2 films each having a thickness of about 70 nm and six ZrO2 films each having a thickness of about 50 nm are formed is formed on a surface of the dielectric multilayer film 270 on a side opposite to the light reflecting surface 2. The light reflecting surface 2 side is kept to have a reflectance of about 98% for a laser beam due to the dielectric multilayer film 280. The dielectric multilayer film 280 shown in
The remaining structure and manufacturing process of the nitride-based semiconductor laser device 210 according to the first modification of the second embodiment are similar to those of the aforementioned second embodiment.
According to the first modification of the second embodiment, as hereinabove described, the dielectric multilayer film 280 is formed to be in contact with the AlOXNY film 272 (thickness of about 60 nm) of the dielectric multilayer film 270, whereby since no Al2O3 film 81 is formed, the manufacturing process in forming the dielectric multilayer film 270 can be simplified as compared with the dielectric multilayer film 70 according to the aforementioned second embodiment. Further, a total thickness of a facet coating film constituted by the dielectric multilayer film 270 and the dielectric multilayer film 280 can be reduced.
A second modification of the second embodiment will be described with reference to
According to the second modification of the second embodiment, a dielectric multilayer film 275 in which an AlN film 71 having a thickness of about 10 nm, an AlOXNY film 72 having a thickness of about 30 nm and an AlN film 273 having a thickness of about 10 nm are formed successively from a side closer to a light reflecting surface 2 is formed on the light reflecting surface 2 of a nitride-based semiconductor laser device 220, as shown in
The remaining structure and manufacturing process of the nitride-based semiconductor laser device 220 according to the second modification of the second embodiment are similar to those of the aforementioned second embodiment.
According to the second modification of the second embodiment, as hereinabove described, the dielectric multilayer film 275 is constituted by the AlN film 71, the AlOXNY film 72 and the AlN film 273, whereby AlN which is a material for suppressing diffusion of oxidation can further suppress diffusion of oxygen contained in the Al2O3 film 81 of the dielectric multilayer film 80 or the like toward the light reflecting surface 2.
A third modification of the second embodiment will be described with reference to
According to the third modification of the second embodiment, a dielectric multilayer film 276 in which an AlN film 71 having a thickness of about 10 nm, an AlOXNY film 72 having a thickness of about 30 nm, an AlN film 273 having a thickness of about 10 nm and an AlOXNY film 274 having a thickness of about 60 nm are formed successively from a side closer to a light reflecting surface 2 is formed on the light reflecting surface 2 of a nitride-based semiconductor laser device 230, as shown in
The remaining structure and manufacturing process of the nitride-based semiconductor laser device 230 according to the third modification of the second embodiment are similar to those of the aforementioned second embodiment.
According to the third modification of the second embodiment, as hereinabove described, the dielectric multilayer film 276 is constituted by the AlN film 71, the AlOXNY film 72, the AlN film 273 and the AlOXNY film 274, whereby since the nitride film (AlN film 273) and the oxide film (SlO2 film 82) are stacked through the oxynitride film (AlOXNY film 274), adhesiveness between the nitride film and the oxynitride film on the contact interface and adhesiveness between the oxynitride film and the oxide film on the contact interface can be improved, in addition to the effects of the aforementioned second modification of the second embodiment.
A third embodiment will be described with reference to
According to the third embodiment, only the dielectric multilayer film 340 in which an AlN film 41 having a thickness of about 10 nm in contact with a light emitting surface 1 and an AlOXNY film 342 having a thickness of about 70 nm in contact with the AlN film 41 are formed successively from a side closer to the light emitting surface 1 is formed on the light emitting surface 1 of the nitride-based semiconductor laser device 300, as shown in
According to the third embodiment, as hereinabove described, only the dielectric multilayer film 340 constituted by the AlN film 41 and the AlOXNY film 342 is formed on the light emitting surface 1, whereby since no Al2O3 film 51 according to the aforementioned first embodiment is formed, the manufacturing process in forming the dielectric multilayer film 340 can be simplified, and a total thickness of the dielectric multilayer film 340 can be reduced.
A confirmatory experiment conducted for confirming the effects of the aforementioned first embodiment will be described with reference to
In this confirmatory experiment, a nitride-based semiconductor laser device 100 (see
In the nitride-based semiconductor laser device 100 according to the aforementioned Example, a composition of oxygen and nitrogen in each dielectric film (analytical points A to C: see
Further, a stress value of each dielectric film was also investigated. More specifically, the AlN film, the AlOXNY film and the Al2O3 film were independently formed on an Si substrate under a condition (temperature, pressure, flow ratio of atmosphere gas, and the like) similar to the formation condition of each dielectric film in the aforementioned Example. Then, stress values of the respective dielectric films were calculated on the basis of measurement data of a warp of an Si substrate formed with no dielectric films and warps of Si substrates formed with respective dielectric films.
Referring to
From the results of calculation of stress of the respective dielectric films, difference in stress value between the AlN film and the Al2O3 film was 10 times. On the other hand, it has been confirmed that the AlOXNY film had an approximate intermediate stress value (about 60%) between the AlN film and the Al2O3 film. Therefore, it has been proved that the AlOXNY film was able to relax large stress difference between the AlN film and the Al2O3 film by holding the AlOXNY film between the AlN film and the Al2O3 film in the nitride-based semiconductor laser device 100 (see
Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.
For example, while the semiconductor element layer 20 is formed by the nitride-based semiconductor layer in each of the aforementioned first to third embodiments, the present invention is not restricted to this but the semiconductor element layer may be formed by a semiconductor material other than the nitride-based semiconductor layer.
While the AlN film and the AlOXNY film are formed in this order on the cavity facets (light emitting and reflecting surfaces 1 and 2) by ECR plasma in the manufacturing process of each of the aforementioned first to third embodiments, the present invention is not restricted to this but the AlOXNY film may be formed in a state where the roughness is formed on the surface of the AlN film by etching after forming the AlN film. The roughness where a maximum value H of the height from the bottom portion of each recess portion to the top portion of the projecting portion adjacent to the recess portion is H <λ/n (n: average refractive index of each insulating film) can be formed by properly adjusting the etching condition.
While the Al2O3 film 51 which is the oxide film is employed for the insulating film controlling the reflectance on the light emitting surface 1 side in the aforementioned first embodiment, the present invention is not restricted to this but the insulating film may be formed by an oxidized compound containing an Si element, a Zr element, a Ta element, an Hf element and a Nb element. For example, an Si3N4 film, other than the aforementioned oxide film, which is a nitride film may be formed. The Si3N4 film is an example of the “third insulating film” in the present invention. For example, an AlON film or an SiON film, different from the aforementioned oxide film and nitride film, which is an oxynitride film may be formed.
While the facet coating film on the light reflecting surface 2 side is formed similarly to the aforementioned first embodiment (dielectric multilayer film 60) in the aforementioned third embodiment, the present invention is not restricted to this but the facet coating film on the light reflecting surface 2 side may be formed similarly to the facet coating film (combination of the dielectric multilayer films 70 and 80) employed in the aforementioned second embodiment or the facet coating film (combination of the dielectric multilayer films 270 and 280) employed in the aforementioned first modification of the second embodiment. Alternately, the facet coating film on the light reflecting surface 2 side may be formed similarly to the facet coating film (combination of the dielectric multilayer films 275 and 80) employed in the aforementioned second modification of the second embodiment or the facet coating film (combination of the dielectric multilayer films 276 and 80) employed in the aforementioned third modification of the second embodiment.
While the AlOXNY film 342 is formed to have a thickness of about 70 nm in each of the aforementioned third embodiment and the modification thereof, the present invention is not restricted to this but the reflectance of the light emitting surface 1 is periodically changed by the thickness of the formed AlOXNY film 342, and hence the thickness of the AlOXNY film 342 for obtaining a desired reflectance may be other than 70 nm described above.
While the multilayer reflecting film (66 or 83) controlling the reflectance on the light reflecting surface 2 side is formed by alternately stacking the six SiO2 films and the six ZrO2 films in each of the aforementioned first to third embodiment, the present invention is not restricted to this but the SiO2 films and the ZrO2 films may be alternately stacked in numbers other than six. Further, different two types of insulating films having other refractive indices other than the SiO2 film and the ZrO2 film may be combined as the multilayer reflecting film. For example, a multilayer reflecting film made of SiO2films and Ta2O5 films may be employed, or a multilayer reflecting film made of SiO2films and Hf2O films may be employed. Alternately, a multilayer reflecting film made of SiO2 films and Nb2O5 films may be employed, or a multilayer reflecting film made of SiO2 films and TiO2 films may be employed. Further, a multilayer reflecting film made of Al2O3 films and Ta2O5 films may be employed or a multilayer reflecting film made of Al2O3 films and Hf2O films may be employed. Alternately, a multilayer reflecting film made of Al2O3 films and Nb2O5 films may be employed, or a multilayer reflecting film made of Al2O3 films and TiO2 films may be employed.
While the semiconductor element layer 20 is so formed on the main surface of the n-type (0001) plane GaN substrate 10 that the ridge 30 extends in a [1-100] direction in each of the aforementioned first to third embodiment, the present invention is not restricted to this but the semiconductor element layer may be formed on an n-type GaN substrate having a main surface, the plane orientation of which is an a-plane ((11-20) plane) or an m-plane ((1-100) plane) so that the nitride-based semiconductor laser device is formed. In particular, when the semiconductor element layer is formed on the main surface of the nonpolar face such as the a-plane or the m-plane, the semiconductor element layer is formed with a ridge extending along a [0001] direction and a (0001) plane and a (000-1) plane of the semiconductor element layer are the “first cavity facet” and the “second cavity facet” in the present invention, respectively. The semiconductor element layer is grown on the a-plane or the m-plane of the n-type GaN substrate, whereby a piezoelectric field caused in the active layer can be further reduced, and hence a nitride-based semiconductor laser device having more improved luminous efficiency can be obtained. When the semiconductor element layer is formed on a main surface of the aforementioned c-plane, a ridge extending along a [11-20] direction can be formed on the semiconductor element layer, for example. In this case, a (11-20) plane and a (−1-120) place of the semiconductor element layer are the “first cavity facet” and the “second cavity facet” in the present invention, respectively. When the semiconductor element layer is formed on the main surface of the aforementioned c-plane, a ridge extending along a [1-100] direction can be formed on the semiconductor element layer. In this case, a (1-100) plane and a (−1-1100) plane of the semiconductor element layer are the “first cavity facet” and the “second cavity facet” in the present invention, respectively.
This application is a divisional of pending U.S. application Ser. No. 12/608,549 filed Oct. 29, 2010 and claims priority to Japanese application number JP2008-279562, entitled, “Semiconductor Laser Device and Method of Manufacturing the Same”, filed Oct. 30, 2008, Yoshiki Murayama et al, the disclosure of which is incorporated herein, in its entirety by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12608549 | Oct 2009 | US |
| Child | 13675779 | US |
