JP2009099958A - Nitride-based semiconductor laser element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitride-based semiconductor laser element whose light emission efficiency is sufficiently improved. <P>SOLUTION: A light emission facet 1F of the nitride-based semiconductor laser element 1 is formed along a (0001) plane, and a rear facet 1B is formed along a (000-1) plane. A first dielectric multilayer film 210 is formed on the light emission facet 1F of the nitride-based semiconductor laser element. The first dielectric multilayer film 210 has a structure of a stack of an AlN film 211 and an Al<SB>2</SB>O<SB>3</SB>film 212 in this order. At the same time, on the rear facet 1B of the nitride-based semiconductor laser element 1, a second dielectric multilayer film 220 is formed. The second dielectric multilayer film 220 has a structure of a stack of an Al<SB>2</SB>O<SB>3</SB>film 221, a reflective film 222, and an AlN film 223 in this order. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a nitride semiconductor laser element having a nitride semiconductor layer.

In recent years, the use of nitride-based semiconductor laser elements has been promoted as a light source for next-generation large-capacity disks, and its development has been actively conducted.
In such a nitride semiconductor laser element, the plane orientation of the main surface of the active layer is set to (H, K, -HK, 0) plane such as (11-20) plane or (1-100) plane. Thus, it is known that the piezoelectric field generated in the active layer can be reduced, and as a result, the light emission efficiency of the laser light can be improved. Here, the above H and K are arbitrary integers, and at least one of H and K is an integer other than 0.
Further, it is known that the gain of a nitride-based semiconductor laser device can be improved by using the (0001) plane and the (000-1) plane as a pair of resonator planes (for example, Patent Document 1). And Non-Patent Document 1).
Japanese Patent Laid-Open No. 8-213692 Japanese Journal of Applied Physics Vol.46, No.9, 2007, pp.L187-L189

In the nitride-based semiconductor laser elements described in Patent Document 1 and Non-Patent Document 1, one (0001) plane of the pair of resonator surfaces is a Ga (gallium) polar plane and the other (000-1). ) Plane is an N (nitrogen) polar plane. The (0001) plane which is a Ga polar plane is easily covered with Ga atoms, and the (000-1) plane which is an N polar plane is easily covered with N atoms.
A protective film made of, for example, an oxide film is formed on the pair of resonator surfaces of the semiconductor laser element.
However, in the above nitride semiconductor laser element, when an oxide film is formed on the (0001) plane, it is caused by the bond between Ga atoms and O (oxygen) atoms at the interface between the (0001) plane and the oxide film. To generate surface levels. Due to the surface level, the laser beam is easily absorbed at the interface between the (0001) plane and the oxide film. Therefore, the light emission efficiency of the laser beam cannot be sufficiently improved.
An object of the present invention is to provide a nitride-based semiconductor laser device with sufficiently improved luminous efficiency.

(1) A nitride-based semiconductor laser device according to the present invention has an optical waveguide extending in the [0001] direction, and has one end face made of a (0001) plane and the other end face made of a (000-1) face as a resonator face. A nitride-based semiconductor layer, a first protective film that is provided on one end face of the nitride-based semiconductor layer, and that is provided on the other end face of the nitride-based semiconductor layer, and that includes oxygen as a constituent element. And a second protective film included.
In this nitride-based semiconductor laser device, one end face composed of the (0001) plane and the other end face composed of the (000-1) plane serve as a pair of resonator surfaces of the optical waveguide extending in the [0001] direction. Laser light is emitted from the end face.
Since one end face made of the (0001) plane is a group 13 element polar plane, it is easily covered with a group 13 element such as gallium. Here, since the first protective film containing nitrogen as a constituent element is provided on one end face, a surface level is generated at the interface between the one end face and the first protective film due to the bond between the group 13 element and oxygen. Is prevented. This prevents the laser light from being absorbed at the surface level at the interface between the one end face and the first protective film.
On the other hand, the other end surface composed of the (000-1) plane is a nitrogen polar surface and is therefore easily covered with nitrogen atoms. Therefore, on the other side, the surface level due to the bond between the group 13 element and oxygen is hardly generated. A second protective film containing oxygen as a constituent element is provided on the other end surface. When the second protective film contains oxygen as a constituent element, the absorption of laser light is smaller than when nitrogen is contained as a constituent element. Therefore, absorption of laser light by the second protective film is suppressed.
As a result, the light emission efficiency of the laser light can be sufficiently improved.
(2) The intensity of the laser beam emitted from the one end surface may be larger than the intensity of the laser beam emitted from the other end surface.
In this case, one end surface composed of the (0001) plane is the main light exit surface. Here, the one end face is chemically stable as compared to the other end face composed of the (000-1) plane. Therefore, at the time of manufacture, the (0001) plane is less likely to have a concavo-convex shape than the (000-1) plane. Thereby, the laser beam is hardly scattered on one end face. Therefore, a good far-field image with little ripple can be obtained efficiently.
(3) The one end face portion of the optical waveguide and the other end face portion of the optical waveguide each have a concavo-convex shape, and the depth of the concavo-convex recess on the one end surface is smaller than the depth of the concavo-convex recess on the other end surface. Also good.
In this case, since the laser beam is not easily scattered on the one end face, a good far-field image with little ripple can be efficiently obtained from the one end face.
(4) The intensity of the laser beam emitted from the other end surface may be larger than the intensity of the laser beam emitted from the one end surface.
In this case, the other end surface composed of the (000-1) plane is the main light exit surface. Here, the one end face composed of the (0001) plane is easily covered with the group 13 element, and thus has a characteristic of being easily oxidized. On the other hand, the other end surface composed of the (000-1) plane is easily covered with nitrogen atoms, and therefore has a characteristic that it is difficult to be oxidized. As a result, deterioration of the main light exit surface due to oxidation is suppressed, and stable high output operation can be realized.
(5) The first protective film may further contain oxygen as a constituent element, and the composition ratio of nitrogen may be larger than the composition ratio of oxygen.
In this case, by further including oxygen as a constituent element, the refractive index of the first protective film can be easily changed by the composition ratio of nitrogen and oxygen, and the degree of freedom in designing the protective film can be increased. . In addition, the composition ratio of the first protective film is such that the ratio of oxygen that generates surface levels due to the bond with the group 13 element at the interface between the one end face and the first protective film is smaller than the ratio of nitrogen. The laser beam is prevented from being absorbed at the surface level at the interface between the one end face and the first protective film.
(6) The second protective film may further contain nitrogen as a constituent element, and the composition ratio of oxygen may be larger than the composition ratio of nitrogen.
In this case, by further including nitrogen as a constituent element, the refractive index of the second protective film can be easily changed by the composition ratio of nitrogen and oxygen, and the degree of freedom in designing the protective film can be increased. . In addition, since the composition ratio of the second protective film is such that the ratio of oxygen that absorbs less laser light is larger than the ratio of nitrogen, laser light is prevented from being absorbed by the second protective film.
In addition, the axial direction and plane orientation of the crystal shown by the optical waveguide extending in the [0001] direction of the present invention, the one end face composed of the (0001) plane, and the other end face composed of the (000-1) plane are as described in (1) above. Similarly to the above, as long as the effect of suppressing the absorption of laser light by the first and second protective films can be obtained, it may be slightly deviated from the axial direction or the plane orientation of the crystal.

  According to the present invention, laser light is prevented from being absorbed at the surface level at the interface between the one end face and the first protective film, and absorption of the laser light by the second protective film is suppressed. Thereby, it is possible to sufficiently improve the light emission efficiency of the laser beam.

1. First embodiment
(1) Structure of nitride semiconductor laser device
1 and 2 are longitudinal sectional views of the nitride-based semiconductor laser device according to the first embodiment. The A1-A1 line in FIG. 1 indicates the vertical cross-sectional position in FIG. 2, and the A2-A2 line in FIG. 2 indicates the vertical cross-sectional position in FIG.
As shown in FIGS. 1 and 2, the nitride-based semiconductor laser device 1 according to the present embodiment has an n-type GaN substrate 101 having a thickness of about 100 μm doped with Si (silicon). The carrier concentration of the substrate 101 is about 5 × 10 ¹⁸ cm ^-3 It is.
The substrate 101 is an off-substrate having a crystal growth surface inclined by about 0.3 degrees in the [000-1] direction from the (11-20) plane. As shown in FIG. 1, a pair of stepped portions ST extending in the [0001] direction is formed on the upper surface of the substrate 101. A pair of stepped portions ST are located on both sides of the substrate 101. Each step ST has a depth of about 0.5 μm and a width of about 20 μm.
On the upper surface of the substrate 101, an n-type layer 102 doped with Si and having a thickness of about 100 nm is formed. The n-type layer 102 is made of n-type GaN, and the doping amount of Si into the n-type layer 102 is about 5 × 10. ¹⁸ cm ^-3 It is.
On the n-type layer 102, an n-type Al doped with Si and having a thickness of about 400 nm. _0.07 Ga _0.93 An n-type cladding layer 103 made of N is formed. The doping amount of Si into the n-type cladding layer 103 is about 5 × 10 ¹⁸ cm ^-3 The carrier concentration of the n-type cladding layer 103 is about 5 × 10 ¹⁸ cm ^-3 It is.
On the n-type cladding layer 103, an n-type Al doped with Si and having a thickness of about 5 nm. _0.16 Ga _0.84 An n-type carrier block layer 104 made of N is formed. The doping amount of Si into the n-type carrier block layer 104 is about 5 × 10 ¹⁸ cm ^-3 The carrier concentration of the n-type carrier block layer 104 is about 5 × 10 ¹⁸ cm ^-3 It is.
On the n-type carrier block layer 104, an n-type light guide layer 105 made of n-type GaN doped with Si and having a thickness of about 100 nm is formed. The doping amount of Si into the n-type light guide layer 105 is about 5 × 10 ¹⁸ cm ^-3 The carrier concentration of the n-type light guide layer 105 is about 5 × 10 ¹⁸ cm ^-3 It is.
An active layer 106 is formed on the n-type light guide layer 105. The active layer 106 has an undoped In thickness of about 20 nm. _0.02 Ga _0.98 Four barrier layers 106a made of N (see FIG. 3 described later) and undoped In having a thickness of about 3 nm _0.6 Ga _0.4 It has an MQW (multiple quantum well) structure in which three well layers 106b made of N (see FIG. 3 described later) are alternately stacked.
A p-type light guide layer 107 made of p-type GaN having a thickness of about 100 nm doped with Mg (magnesium) is formed on the active layer 106. The doping amount of Mg into the p-type light guide layer 107 is about 4 × 10. ¹⁹ cm ^-3 The carrier concentration of the p-type light guide layer 107 is about 5 × 10 ¹⁷ cm ^-3 It is.
On the p-type light guide layer 107, Mg-doped p-type Al having a thickness of about 20 nm. _0.16 Ga _0.84 A p-type cap layer 108 made of N is formed. The doping amount of Mg into the p-type cap layer 108 is about 4 × 10. ¹⁹ cm ^-3 The carrier concentration of the p-type cap layer 108 is about 5 × 10 ¹⁷ cm ^-3 It is.
On the p-type cap layer 108, p-type Al doped with Mg. _0.07 Ga _0.93 A p-type cladding layer 109 made of N is formed. The doping amount of Mg into the p-type cladding layer 109 is about 4 × 10 ¹⁹ cm ^-3 The carrier concentration of the p-type cap layer 108 is about 5 × 10 ¹⁷ cm ^-3 It is.
Here, the p-type cladding layer 109 includes a flat portion 109b formed on the p-type cap layer 108 and a convex portion 109a formed in the central portion on the flat portion 109b so as to extend in the [0001] direction. Have.
The thickness of the flat portion 109b of the p-type cladding layer 109 is about 80 nm, and the height from the upper surface of the flat portion 109b to the upper surface of the convex portion 109a is about 320 nm. Further, the width of the convex portion 109a is about 1.75 μm.
On the protrusion 109a of the p-type cladding layer 109, a p-type In doped with Mg and having a thickness of about 10 nm. _0.02 Ga _0.98 A p-type contact layer 110 made of N is formed. The doping amount of Mg into the p-type contact layer 110 is about 4 × 10 ¹⁹ cm ^-3 The carrier concentration of the p-type contact layer 110 is about 5 × 10 ¹⁷ cm ^-3 It is.
A ridge portion Ri is constituted by the convex portion 109 a of the p-type cladding layer 109 and the p-type contact layer 110. As a result, the optical waveguide WG along the [0001] direction is formed below the ridge Ri and in a portion including the active layer 106.
An ohmic electrode 111 is formed on the p-type contact layer 110. The ohmic electrode 111 has a structure in which Pt (platinum), Pd (palladium), and Au (gold) are stacked in this order. The film thicknesses of Pt, Pd and Au are about 5 nm, about 100 nm and about 150 nm, respectively.
A current confinement layer 112 made of an insulating film having a thickness of about 250 nm is formed so as to cover the upper surface of the flat portion 109b, the upper surface of the n-type cladding layer 103, and the side surfaces of the respective layers 103 to 111. In this example, the insulating film is SiO. ₂ A (silicon oxide) film is used.
A pad electrode 113 is formed on the upper surface of the ohmic electrode 111 and predetermined regions on the side surface and upper surface of the current confinement layer 112. The pad electrode 113 has a structure in which Ti (titanium), Pd, and Au are laminated in this order. The thicknesses of Ti, Pd, and Au are about 100 nm, about 100 nm, and about 3 μm, respectively.
An n-side electrode 114 is formed on the back surface of the substrate 101. The n-side electrode 114 has a structure in which Al (aluminum), Pt, and Au are laminated in this order. The thicknesses of Al, Pt and Au are about 10 nm, about 20 nm and about 300 nm, respectively.
N-type cladding layer 103, n-type carrier block layer 104, n-type light guide layer 105, active layer 106, p-type light guide layer 107, p-type cap layer 108, p-type cladding layer 109 and p-type contact layer 110 are nitrided A physical semiconductor layer is formed.
Here, of the pair of resonator surfaces of the nitride-based semiconductor laser device 1, a resonator surface having a low reflectance is referred to as a light emitting surface, and a resonator surface having a high reflectance is referred to as a rear surface.
As shown in FIG. 2, the light emitting surface 1F of the nitride semiconductor laser element 1 is a (0001) cleaved surface, and the rear surface 1B is a (000-1) cleaved surface. Thereby, the light emission surface 1F becomes a Ga (gallium) polar surface, and the rear surface 1B becomes an N (nitrogen) polar surface. A portion of the light emitting surface 1F located in the optical waveguide WG and a portion of the rear surface 1B located in the optical waveguide WG form a pair of resonator surfaces.
A first dielectric multilayer film 210 is formed on the light emitting surface 1 </ b> F of the nitride semiconductor laser element 1. The first dielectric multilayer film 210 includes an AlN film 211 and an AlN film. ₂ O ₃ The film 212 has a stacked structure in this order. Thereby, the AlN film 211 which is a nitride film functions as a protective film for the light emitting surface 1F.
AlN film 211 and Al ₂ O ₃ The thickness of the film 212 is about 10 nm and about 85 nm, respectively. The reflectance of the first dielectric multilayer film 210 is about 8%.
On the other hand, a second dielectric multilayer film 220 is formed on the rear surface 1B of the nitride-based semiconductor laser device 1. The second dielectric multilayer film 220 is made of Al. ₂ O ₃ The film 221, the reflective film 222, and the AlN film 223 are stacked in this order. As a result, the oxide film Al ₂ O ₃ The film 221 functions as a protective film for the rear surface 1B.
Al ₂ O ₃ The film 221 has a thickness of 120 nm. The reflective film 222 is made of SiO having a thickness of about 70 nm. ₂ A TiO 2 film and a film thickness of about 45 nm ₂ The film has a 10-layer structure in which 5 layers are alternately stacked one by one. SiO ₂ The film is used as a low refractive index film, TiO ₂ The film is used as a high refractive index film. The thickness of the AlN film 223 is about 10 nm. The reflectance of the second dielectric multilayer film 220 is about 95%.
When a voltage is applied between the pad electrode 113 and the n-side electrode 114 of the nitride semiconductor laser element 1 described above, laser light is emitted from the light emitting surface 1F and the rear surface 1B.
In the present embodiment, as described above, the first dielectric multilayer film 210 having a reflectance of about 8% is provided on the light emitting surface 1F, and the second dielectric multilayer film having a reflectance of about 95% is provided on the rear surface 1B. 220 is provided. As a result, the intensity of the laser light emitted from the light emitting surface 1F is significantly higher than the intensity of the laser light emitted from the rear surface 1B. That is, the light emission surface 1F becomes the main emission surface of the laser light.
(2) Details of light exit surface 1F and rear surface 1B
3 and 4 are partially enlarged cross-sectional views of the nitride-based semiconductor laser device 1 of FIG. FIG. 3 shows an enlarged sectional view of the light emitting surface 1F and its vicinity in the optical waveguide WG, and FIG. 4 shows an enlarged sectional view of the rear surface 1B and its vicinity in the optical waveguide WG.
As shown in FIGS. 3 and 4, the active layer 106 has a structure in which four barrier layers 106a and three well layers 106b are alternately stacked. In the light emitting surface 1F and the rear surface 1B, the well layer 106b of the active layer 106 protrudes outward from the other layers of the nitride-based semiconductor layer. Therefore, irregularities are formed on the active layer 106 on the light emitting surface 1F and the rear surface 1B.
The depth D1 (FIG. 3) of the concave and convex portions of the unevenness of the active layer 106 on the light emission surface 1F is about 1 nm. On the other hand, the depth D2 (FIG. 4) of the concave / convex concave portion of the active layer 106 on the rear surface 1B of the nitride-based semiconductor laser device 1 is about 6 nm. The high refractive index film (TiO 2) of the reflective film 222 ₂ Film) and low refractive index film (SiO2) ₂ Thin film (in this example, TiO) ₂ The thickness of the film) is adjusted to be larger than the depth D2 of the concave and convex portions on the rear surface 1B. In this case, the second dielectric multilayer film 220 can be easily formed so as to reliably cover the unevenness of the rear surface 1B. Thereby, a high reflectance of the second dielectric multilayer film 220 can be ensured.
The reason why irregularities are formed in the active layer 106 is as follows. As will be described later, when the nitride semiconductor laser device 1 is manufactured, the light emitting surface 1F and the rear surface 1B are cleaned. In this cleaning step, ECR (electron cyclotron resonance) plasma is applied to the light emitting surface 1F and the rear surface 1B. Thereby, the light emission surface 1F and the rear surface 1B are etched.
Here, the composition of the well layer 106b of the active layer 106 is greatly different from the composition of other layers of the nitride-based semiconductor layer such as the barrier layer 106a, the n-type light guide layer 105, and the p-type light guide layer 107. Therefore, there is a difference between the etching amount of the well layer 106b of the active layer 106 and the etching amount of other layers of the nitride-based semiconductor layer. Thereby, irregularities are formed in the active layer 106 on the light emitting surface 1F and the rear surface 1B.
As the In composition ratio of the well layer 106b is higher, the unevenness becomes more prominent. This is because when the In composition ratio of the well layer 106b is larger than the Ga composition ratio (when 0.5 <x ≦ 1), the difference between the composition of the well layer 106b and the composition of other layers becomes larger. Because. In the present embodiment, the In composition ratio x of the well layer 106b is 0.6.
In particular, the (000-1) plane of the nitride-based semiconductor layer is chemically more unstable than the (0001) plane. Therefore, the difference in etching amount between the well layer 106b and the other layer on the (000-1) plane is larger than the difference in etching amount between the well layer 106b and the other layer on the (0001) plane. As a result, the depth D2 of the concave / convex concave portion of the rear surface 1B becomes larger than the depth D1 of the concave / convex concave portion of the light emitting surface 1F.
When the depth of the concave and convex portions on the cavity surface increases, the laser light is greatly scattered by the concave and convex portions. In the present embodiment, since the light exit surface 1F is composed of a (0001) surface with small irregularities, the scattering of the laser light on the light exit surface 1F can be suppressed. As a result, it is possible to obtain a good far-field image with little ripple during laser oscillation.
(3) Manufacturing method of nitride-based semiconductor laser device 1
A method for manufacturing the nitride-based semiconductor laser device 1 having the above configuration will be described.
First, a substrate 101 having a plurality of grooves G (see FIG. 1) extending in the [0001] direction formed on the upper surface is prepared. The depth of the groove G is about 0.5 μm and the width is about 40 μm. The interval between two adjacent grooves G is about 400 μm. The groove G is formed in advance in order to chip the element in a later process. A part of the groove G constitutes the above-described stepped portion ST.
An n-type layer 102 having a thickness of about 100 nm, an n-type cladding layer 103 having a thickness of about 400 nm, an n-type carrier block layer 104 having a thickness of about 5 nm, an n-type light guide layer 105 having a thickness of about 100 nm, and a thickness of about 100 nm. For example, an active layer 106 having a thickness of 90 nm, a p-type light guide layer 107 having a thickness of about 100 nm, a p-type cap layer 108 having a thickness of about 20 nm, a p-type cladding layer 109 having a thickness of about 400 nm, and a p-type contact layer 110 having a thickness of about 10 nm The layers are sequentially formed by metal vapor phase epitaxy (MOVPE).
The thickness of the active layer 106 represents the total thickness of the four barrier layers 106a and the three well layers 106b.
Thereafter, p-type annealing treatment and formation of the ridge Ri in FIG. 1 are performed. In addition, the ohmic electrode 111, the current confinement layer 112, and the pad electrode 113 are formed. Further, the n-side electrode 114 is formed on the back surface of the substrate 101.
Subsequently, the resonator surfaces (light emitting surface 1F and rear surface 1B) are formed as described below, and the first dielectric multilayer film 210 and the second dielectric multilayer film 220 are formed on the resonator surface.
A scribe flaw extending in the [1-100] direction is formed on the substrate 101 on which each of the layers 102 to 110, the ohmic electrode 111, the current confinement layer 112, and the pad electrode 113 are formed. The scribe scratch is formed in a broken line shape in a portion excluding the ridge Ri by laser scribe or mechanical scribe.
Next, the substrate 101 is cleaved so that the light emitting surface 1F and the rear surface 1B are formed. Thereby, the substrate 101 is separated into a rod shape.
Thereafter, the separated substrate 101 is introduced into an ECR sputtering film forming apparatus.
ECR plasma is irradiated to the light emission surface 1F for 5 minutes. The plasma is N of about 0.02 Pa. ₂ It is generated in a gas atmosphere under conditions of a microwave output of 500 W. Thereby, the light emitting surface 1F is cleaned and slightly etched. At this time, RF power (high frequency power) is not applied to the sputtering target. Thereafter, a first dielectric multilayer film 210 (see FIG. 2) is formed on the light emitting surface 1F by ECR sputtering.
Similarly, the rear surface 1B is irradiated with plasma for 5 minutes. Thus, the rear surface 1B is cleaned and slightly etched. At this time, RF power is not applied to the sputtering target. Thereafter, a second dielectric multilayer film 220 (see FIG. 2) is formed on the rear surface 1B by ECR sputtering.
Thus, by cleaning the light emission surface 1F and the rear surface 1B with ECR plasma, the deterioration of the resonator surface and the occurrence of optical destruction of the resonator surface are suppressed. Thereby, the laser characteristics of the nitride-based semiconductor laser device 1 can be improved.
Thereafter, the rod-shaped substrate 101 is separated into chips at the center of the groove G formed on the substrate 101. Thereby, the nitride-based semiconductor laser device 1 of FIG. 1 is completed.
2. Second embodiment
The nitride semiconductor laser element according to the second embodiment will be described while referring to differences from the nitride semiconductor laser element 1 according to the first embodiment.
FIG. 5 is a longitudinal sectional view of a nitride-based semiconductor laser device according to the second embodiment. FIG. 5 shows a longitudinal sectional view of the nitride-based semiconductor laser device 1 along the [0001] direction, similar to the longitudinal sectional view of FIG. 2 in the first embodiment. 5 is the same as the longitudinal sectional view of the nitride-based semiconductor laser device 1 in FIG.
A first dielectric multilayer film 210 is formed on the light emitting surface 1 </ b> F of the nitride semiconductor laser element 1. The first dielectric multilayer film 210 is made of AlO. _X N _Y Film (X <Y) 211a and Al ₂ O ₃ The film 212a has a stacked structure in this order. Where AlO _X N _Y The refractive index of the film 211a is about 1.9. AlO which is an oxynitride film in which the composition ratio of nitrogen is larger than the composition ratio of oxygen _X N _Y The film 211a functions as a protective film for the light emitting surface 1F.
AlO _X N _Y Film 211a and Al ₂ O ₃ The film thickness of the film 212a is about 30 nm and about 65 nm, respectively. The reflectance of the first dielectric multilayer film 210 is about 8%.
On the other hand, a second dielectric multilayer film 220 is formed on the rear surface 1B of the nitride-based semiconductor laser device 1. The second dielectric multilayer film 220 is made of AlO. _X N _Y The film (X> Y) 221a and the reflective film 222a are stacked in this order. AlO _X N _Y The refractive index of the film 221a is about 1.7. AlO is an oxynitride film in which the composition ratio of oxygen is larger than the composition ratio of nitrogen _X N _Y The film 221a functions as a protective film for the rear surface 1B.
AlO _X N _Y The film thickness of the film 221a is about 30 nm. The reflective film 222a is made of SiO with a film thickness of about 70 nm. ₂ A TiO 2 film and a film thickness of about 45 nm ₂ The film has a 10-layer structure in which 5 layers are alternately stacked one by one. SiO ₂ The film is used as a low refractive index film, TiO ₂ The film is used as a high refractive index film. The reflectance of the second dielectric multilayer film 220 is about 95%.
3. Third embodiment
The nitride semiconductor laser element according to the third embodiment will be described while referring to differences from the nitride semiconductor laser element 1 according to the first embodiment.
FIG. 6 is a longitudinal sectional view of a nitride-based semiconductor laser device according to the third embodiment. FIG. 6 shows a longitudinal sectional view of the nitride-based semiconductor laser device 1 along the [0001] direction, similarly to the longitudinal sectional view of FIG. 2 in the first embodiment. 6 is the same as the longitudinal sectional view of the nitride-based semiconductor laser device 1 in FIG.
A first dielectric multilayer film 210 is formed on the light emitting surface 1 </ b> F of the nitride semiconductor laser element 1. The first dielectric multilayer film 210 includes an AlN film 211b, AlO _X N _Y Film (X <Y) 212b and Al ₂ O ₃ The film 213b has a stacked structure in this order. AlO _X N _Y The refractive index of the film 211b is about 1.9. The AlN film 211b, which is a nitride film, functions as a protective film for the light emitting surface 1F.
AlN film 211b, AlO _X N _Y Film 212b and Al ₂ O ₃ The film thickness of the film 213b is about 10 nm, about 30 nm, and about 62 nm, respectively. The reflectance of the first dielectric multilayer film 210 is about 8%.
On the other hand, a second dielectric multilayer film 220 is formed on the rear surface 1B of the nitride-based semiconductor laser device 1. The second dielectric multilayer film 220 is made of Al. ₂ O ₃ Film 221b, AlO _X N _Y Film (X <Y) 222b, Al ₂ O ₃ The film 223b and the reflective film 224b have a structure in which they are stacked in this order. AlO _X N _Y The refractive index of the film 222b is about 1.9. Al is an oxide film ₂ O ₃ The film 221b functions as a protective film for the rear surface 1B.
Al ₂ O ₃ Film 221b, AlO _X N _Y Film 222b and Al ₂ O ₃ The film thickness of the film 223b is about 60 nm, about 30 nm, and about 60 nm. The reflective film 224b is made of SiO with a film thickness of about 70 nm. ₂ A TiO 2 film and a film thickness of about 45 nm ₂ The film has a 10-layer structure in which 5 layers are alternately stacked one by one. SiO ₂ The film is used as a low refractive index film, TiO ₂ The film is used as a high refractive index film. The reflectance of the second dielectric multilayer film 220 is about 95%.
4). Fourth embodiment
The nitride semiconductor laser element according to the fourth embodiment will be described while referring to differences from the nitride semiconductor laser element 1 according to the first embodiment.
FIG. 7 is a longitudinal sectional view of a nitride-based semiconductor laser device according to the fourth embodiment. FIG. 7 shows a longitudinal sectional view of the nitride-based semiconductor laser device 1 along the [0001] direction, similar to the longitudinal sectional view of FIG. 2 in the first embodiment. A vertical cross-sectional view taken along line A2-A2 of FIG. 7 is the same as the vertical cross-sectional view of the nitride-based semiconductor laser device 1 of FIG.
A first dielectric multilayer film 210 is formed on the light emitting surface 1 </ b> F of the nitride semiconductor laser element 1. The first dielectric multilayer film 210 is made of AlO. _X N _Y Film (X <Y) 211c, AlO _X N _Y Film (X> Y) 212c and Al ₂ O ₃ The film 213c has a structure in which the films are stacked in this order. AlO _X N _Y The refractive index of the film 211c is about 1.9, and AlO _X N _Y The refractive index of the film 212c is about 1.7. AlO which is an oxynitride film in which the composition ratio of nitrogen is larger than the composition ratio of oxygen _X N _Y The film 211c functions as a protective film for the light emitting surface 1F.
AlO _X N _Y Film 211c, AlO _X N _Y Film 212c and Al ₂ O ₃ The film thickness of the film 213c is about 30 nm, about 30 nm, and about 35 nm, respectively. The reflectance of the first dielectric multilayer film 210 is about 8%.
On the other hand, a second dielectric multilayer film 220 is formed on the rear surface 1B of the nitride-based semiconductor laser device 1. The second dielectric multilayer film 220 is made of AlO. _X N _Y Film (X> Y) 221c, AlO _X N _Y The film (X <Y) 222c and the reflective film 223c are stacked in this order. AlO _X N _Y The refractive index of the film 221c is about 1.7, and AlO _X N _Y The refractive index of the film 222c is about 1.9. AlO is an oxynitride film in which the composition ratio of oxygen is larger than the composition ratio of nitrogen _X N _Y The film 221c functions as a protective film for the rear surface 1B.
AlO _X N _Y Film (X> Y) 221c and AlO _X N _Y The film thickness (X <Y) 222c is about 30 nm and about 30 nm. The reflective film 223c is made of SiO with a film thickness of about 70 nm. ₂ A TiO 2 film and a film thickness of about 45 nm ₂ The film has a 10-layer structure in which 5 layers are alternately stacked one by one. SiO ₂ The film is used as a low refractive index film, TiO ₂ The film is used as a high refractive index film. The reflectance of the second dielectric multilayer film 220 is about 95%.
5). Correspondence between each component of claim and each part of embodiment
Hereinafter, although the example of a response | compatibility with each component of a claim and each part of embodiment is demonstrated, this invention is not limited to the following example.
In the first to fourth embodiments, the optical waveguide WG is an example of an optical waveguide extending in the [0001] direction, the light emission surface 1F is an example of one end surface composed of a (0001) surface, and the rear surface 1B. Is an example of the other end surface composed of the (000-1) plane.
The light exit surface 1F and the rear surface 1B are examples of resonator surfaces, and include an n-type cladding layer 103, an n-type carrier block layer 104, an n-type light guide layer 105, an active layer 106, a p-type light guide layer 107, p The nitride-based semiconductor layer formed by the type cap layer 108, the p-type cladding layer 109, and the p-type contact layer 110 is an example of a nitride-based semiconductor layer.
In the first embodiment, the AlN film 211 is an example of a first protective film containing nitrogen as a constituent element. ₂ O ₃ The film 221 is an example of a second protective film containing oxygen as a constituent element. In the second embodiment, AlO _X N _Y The film (X <Y) 211a is an example of a first protective film containing nitrogen as a constituent element. _X N _Y The film (X> Y) 221a is an example of a second protective film containing oxygen as a constituent element. In the third embodiment, the AlN film 211b is an example of a first protective film containing nitrogen as a constituent element. ₂ O ₃ The film 221b is an example of a second protective film containing oxygen as a constituent element. In the fourth embodiment, AlO _X N _Y The film (X <Y) 211c is an example of a first protective film containing nitrogen as a constituent element. _X N _Y The film (X> Y) 221c is an example of a second protective film containing oxygen as a constituent element.
As each constituent element in the claims, various other elements having configurations or functions described in the claims can be used.
6). Effects in the first to fourth embodiments
In the nitride-based semiconductor laser devices according to the first to fourth embodiments, a pair of optical waveguides in which one end surface composed of the (0001) plane and the other end surface composed of the (000-1) plane extend in the [0001] direction. The laser beam is emitted from one end surface and the other end surface.
Since one end face made of the (0001) plane is a group 13 element polar plane, it is easily covered with a group 13 element such as gallium. Here, since the first protective film containing nitrogen as a constituent element is provided on one end face, a surface level is generated at the interface between the one end face and the first protective film due to the bond between the group 13 element and oxygen. Is prevented. This prevents the laser light from being absorbed at the surface level at the interface between the one end face and the first protective film.
On the other hand, the other end surface composed of the (000-1) plane is a nitrogen polar surface and is therefore easily covered with nitrogen atoms. Therefore, the surface level due to the bond between the group 13 element and oxygen is unlikely to occur on the other end surface. A second protective film containing oxygen as a constituent element is provided on the other end surface. When the second protective film contains oxygen as a constituent element, the absorption of laser light is smaller than when nitrogen is contained as a constituent element. Therefore, absorption of laser light by the second protective film is suppressed.
As a result, the light emission efficiency of the laser light can be sufficiently improved.
Further, the intensity of the laser beam emitted from the one end surface is greater than the intensity of the laser beam emitted from the other end surface.
In this case, one end surface composed of the (0001) plane is the main light exit surface. Here, the one end face is chemically stable as compared to the other end face composed of the (000-1) plane. Therefore, at the time of manufacture, the (0001) plane is less likely to have a concavo-convex shape than the (000-1) plane. Thereby, the laser beam is hardly scattered on one end face. Therefore, a good far-field image with little ripple can be obtained efficiently.
The part of the one end face in the optical waveguide and the part of the other end face in the optical waveguide each have a concavo-convex shape, and the depth of the concavo-convex recess on the one end face is smaller than the depth of the concavo-convex recess on the other end face.
In this case, since the laser beam is not easily scattered on the one end face, a good far-field image with little ripple can be efficiently obtained from the one end face.
(A) Effects relating to the protective film covering the light emitting surface 1F and the rear surface 1B
In the first embodiment, the AlN film 211 is formed so as to cover the light emitting surface 1F. That is, a nitride film is formed on the (0001) plane which is a Ga polar plane. In this case, the generation of surface states due to the bonding of Ga atoms and O atoms at the interface between the light emitting surface 1F and the AlN film 211 is prevented. This prevents the laser light from being absorbed at the surface level at the interface between the light emitting surface 1F and the AlN film 211. Accordingly, it is possible to sufficiently improve the light emission efficiency of the laser light.
In the first embodiment, Al is covered so as to cover the rear surface 1B. ₂ O ₃ A film 221 is formed. That is, the oxide film is formed on the (000-1) plane which is the N polar plane. The amount of laser light absorbed by the oxide film is smaller than the amount of laser light absorbed by the nitride film. Also, surface states are unlikely to occur at the interface between the (000-1) plane which is an N-polar plane and the oxide film. Therefore, by forming an oxide film on the (000-1) plane, it becomes possible to improve the light emission efficiency of the laser beam more sufficiently.
In the second embodiment, AlO, which is a nitride film in which the nitrogen composition ratio is larger than the oxygen composition ratio, is formed on the light emission surface 1F made of the (0001) plane. _X N _Y A film (X <Y) 211a is formed. Thereby, it is possible to sufficiently improve the light emission efficiency of the laser beam. Further, AlO, which is an oxide film in which the composition ratio of oxygen is larger than the composition ratio of nitrogen, is formed on the rear surface 1B composed of the (000-1) plane. _X N _Y A film (X> Y) 221a is formed. Thereby, it is possible to sufficiently improve the light emission efficiency of the laser beam. Further, the refractive index of the first or second protective film can be easily changed by the composition ratio of nitrogen and oxygen, and the degree of freedom in designing the protective film can be increased.
In the third embodiment, an AlN film 211b, which is a nitride film, is formed on the light emission surface 1F made of the (0001) plane. Thereby, it is possible to sufficiently improve the light emission efficiency of the laser beam. Further, the rear surface 1B made of the (000-1) plane has Al as an oxide film. ₂ O ₃ A film 221b is formed. Thereby, it is possible to sufficiently improve the light emission efficiency of the laser beam.
In the fourth embodiment, AlO, which is a nitride film in which the nitrogen composition ratio is larger than the oxygen composition ratio, is formed on the light emission surface 1F made of the (0001) plane. _X N _Y A film (X <Y) 211c is formed. Thereby, it is possible to sufficiently improve the light emission efficiency of the laser beam. Further, AlO, which is an oxide film in which the composition ratio of oxygen is larger than the composition ratio of nitrogen, is formed on the rear surface 1B composed of the (000-1) plane. _X N _Y A film (X> Y) 221c is formed. Thereby, it is possible to sufficiently improve the light emission efficiency of the laser beam. Further, the refractive index of the first or second protective film can be easily changed by the composition ratio of nitrogen and oxygen, and the degree of freedom in designing the protective film can be increased.
(B) Effect of (0001) plane being light exit surface 1F
In the present embodiment, since the (0001) plane is the light emitting surface 1F, the depth of the concave and convex portions on the light emitting surface 1F is smaller than the depth of the concave and convex portions on the rear surface 1B. Thereby, scattering of the laser beam on the light emitting surface 1F can be suppressed. As a result, a good far-field image with little ripple can be obtained during the operation of the nitride-based semiconductor laser device 1.
In addition, since the second dielectric multilayer film 220 having a high reflectance is formed on the rear surface 1B, even if a part of the laser light is scattered by the unevenness of the rear surface 1B, the influence of the decrease in the amount of reflection due to the scattering is small. . As a result, a decrease in the output of the laser beam is suppressed.
7). Fifth embodiment
(1) Structure of nitride semiconductor laser device
The nitride semiconductor laser element according to the fifth embodiment will be described while referring to differences from the nitride semiconductor laser element 1 according to the first embodiment.
FIG. 8 is a longitudinal sectional view of a nitride semiconductor laser element according to the fifth embodiment. FIG. 8 shows a longitudinal sectional view of the nitride-based semiconductor laser device 1 along the [0001] direction, similar to the longitudinal sectional view of FIG. 2 in the first embodiment. 8 is the same as the longitudinal sectional view of the nitride-based semiconductor laser device 1 in FIG.
As shown in FIG. 8, in this nitride-based semiconductor laser device 1, the light exit surface 1Fa is a (000-1) cleaved surface, and the rear surface 1Ba is a (0001) cleaved surface.
A third dielectric multilayer film 230 is formed on the light emitting surface 1Fa. The third dielectric multilayer film 230 is made of Al. ₂ O ₃ Film 231, AlN film 232 and SiO ₂ The film 233 has a structure in which the films are stacked in this order. As a result, the oxide film Al ₂ O ₃ The film 231 functions as a protective film for the light emitting surface 1Fa.
Al ₂ O ₃ Film 231, AlN film 232 and SiO ₂ The film thickness of the film 233 is about 120 nm, about 10 nm, and about 95 nm, respectively. The reflectance of the third dielectric multilayer film 230 is about 7%.
A fourth dielectric multilayer film 240 is formed on the rear surface 1Ba. The fourth dielectric multilayer film 240 has a structure in which an AlN film 241, a reflective film 242 and an AlN film 243 are laminated in this order. Thereby, the AlN film 241 which is a nitride film functions as a protective film for the rear surface 1Ba.
The film thickness of the AlN films 241 and 243 is 10 nm. The reflective film 242 is made of SiO having a film thickness of about 70 nm. ₂ TiO with a film thickness of about 45 nm ₂ The film has a 10-layer structure in which 5 layers are alternately stacked one by one. SiO ₂ The film is used as a low refractive index film, TiO ₂ The film is used as a high refractive index film. The reflectance of the fourth dielectric multilayer film 240 is about 95%.
In nitride-based semiconductor laser device 1 formed in this way, laser light is emitted from light emitting surface 1Fa and rear surface 1Ba by applying a voltage between pad electrode 113 and n-side electrode 114. .
In the present embodiment, as described above, the third dielectric multilayer film 230 having a reflectivity of about 7% is provided on the light emitting surface 1Fa, and the fourth dielectric multilayer film having a reflectivity of about 95% is provided on the rear surface 1Ba. 240 is provided. Thereby, the intensity of the laser beam emitted from the light emitting surface 1Fa is larger than the intensity of the laser beam emitted from the rear surface 1Ba. That is, the light emission surface 1Fa is the main emission surface of the laser light.
Here, in this embodiment, the undoped In as the barrier layer 106a of the active layer 106 _0.02 Ga _0.98 N is used as the well layer 106b of the active layer 106. _0.15 Ga _0.85 N is used.
Thus, in the nitride-based semiconductor laser device 1 according to the present embodiment, the In composition ratio in the well layer 106b is 0.15, which is extremely smaller than the Ga composition ratio. Thereby, the unevenness of the active layer 106 is sufficiently suppressed from increasing on the light emitting surface 1Fa and the rear surface 1Ba.
(2) Manufacturing method of nitride-based semiconductor laser device 1
The manufacturing method of the nitride-based semiconductor laser device 1 having the above configuration will be described with respect to differences from the first embodiment.
At the time of manufacturing the nitride-based semiconductor laser device 1 according to the present embodiment, the n-type layer 102, the n-type cladding layer 103, the n-type carrier block layer 104, the n-type light guide layer 105, the active layer 106, the p-type The substrate 101 on which the light guide layer 107, the p-type cap layer 108, the p-type cladding layer 109, and the p-type contact layer 110 are formed has a light emitting surface 1Fa made of a (000-1) surface and a rear surface made of a (0001) surface. Cleavage to form 1Ba.
Thereafter, the third dielectric multilayer film 230 is formed on the cleaned light emitting surface 1Fa by ECR sputtering. A fourth dielectric multilayer film 240 is formed on the cleaned rear surface 1Ba by ECR sputtering.
Thereafter, the rod-shaped substrate 101 is separated into chips at the center of the groove G formed on the substrate 101. Thereby, the nitride-based semiconductor laser device 1 according to the fifth embodiment in FIG. 8 is completed.
8). Sixth embodiment
The nitride semiconductor laser element according to the sixth embodiment will be described while referring to differences from the nitride semiconductor laser element 1 according to the fifth embodiment.
FIG. 9 is a longitudinal sectional view of a nitride-based semiconductor laser device according to the sixth embodiment. FIG. 9 shows a longitudinal sectional view of the nitride-based semiconductor laser device 1 along the [0001] direction, similarly to the longitudinal sectional view of FIG. 2 in the first embodiment. 9 is the same as the longitudinal sectional view of the nitride-based semiconductor laser device 1 in FIG.
A third dielectric multilayer film 230 is formed on the light emitting surface 1Fa. The third dielectric multilayer film 230 is made of AlO. _X N _Y Film (X> Y) 231a and Al ₂ O ₃ The film 232a has a structure in which the films are stacked in this order. AlO _X N _Y The refractive index of the film 231a is about 1.7. AlO is an oxynitride film in which the composition ratio of oxygen is larger than the composition ratio of nitrogen _X N _Y The film 231a functions as a protective film for the light emitting surface 1Fa.
AlO _X N _Y Film 231a and Al ₂ O ₃ The film thickness of the film 232a is about 30 nm and about 57 nm, respectively. The reflectance of the third dielectric multilayer film 230 is about 8%.
A fourth dielectric multilayer film 240 is formed on the rear surface 1Ba. The fourth dielectric multilayer film 240 is made of AlO. _X N _Y A film (X <Y) 241a and a reflective film 242a are stacked in this order. AlO _X N _Y The refractive index of the film 241a is about 1.9. AlO which is an oxynitride film in which the composition ratio of nitrogen is larger than the composition ratio of oxygen _X N _Y The film 241a functions as a protective film for the rear surface 1Ba.
AlO _X N _Y The film thickness of the film 241a is about 30 nm. The reflective film 242a is made of SiO having a thickness of about 70 nm. ₂ A TiO 2 film and a film thickness of about 45 nm ₂ The film has a 10-layer structure in which 5 layers are alternately stacked one by one. SiO ₂ The film is used as a low refractive index film, TiO ₂ The film is used as a high refractive index film. The reflectance of the fourth dielectric multilayer film 240 is about 95%.
9. Seventh embodiment
The nitride semiconductor laser element according to the seventh embodiment will be described while referring to differences from the nitride semiconductor laser element 1 according to the fifth embodiment.
FIG. 10 is a longitudinal sectional view of a nitride-based semiconductor laser device according to the seventh embodiment. FIG. 10 shows a longitudinal sectional view of the nitride-based semiconductor laser device 1 along the [0001] direction, similarly to the longitudinal sectional view of FIG. 2 in the first embodiment. A vertical cross-sectional view taken along line A2-A2 of FIG. 10 is the same as the vertical cross-sectional view of the nitride-based semiconductor laser device 1 of FIG.
A third dielectric multilayer film 230 is formed on the light emitting surface 1Fa. The third dielectric multilayer film 230 is made of Al. ₂ O ₃ Film 231b, AlO _X N _Y Film (X <Y) 232b and Al ₂ O ₃ The film 233b has a stacked structure in this order. AlO _X N _Y The refractive index of the film 232b is about 1.9. Al is an oxide film ₂ O ₃ The film 231b functions as a protective film for the light emitting surface 1Fa.
Al ₂ O ₃ Film 231b, AlO _X N _Y Film 232b and Al ₂ O ₃ The film thickness of the film 233b is about 10 nm, about 30 nm, and about 52 nm, respectively. The reflectance of the third dielectric multilayer film 230 is about 8%.
A fourth dielectric multilayer film 240 is formed on the rear surface 1Ba. The fourth dielectric multilayer film 240 includes an AlN film 241b, an AlO film. _X N _Y Film (X <Y) 242b, Al ₂ O ₃ The film 243b and the reflective film 244b have a structure in which they are stacked in this order. AlO _X N _Y The refractive index of the film 242b is about 1.9. The AlN film 241b, which is a nitride film, functions as a protective film for the rear surface 1Ba.
AlN film 241b, AlO _X N _Y Film 242b and Al ₂ O ₃ The film thickness of the film 243b is about 10 nm, about 30 nm, and about 60 nm. The reflective film 244b is made of SiO having a thickness of about 70 nm. ₂ A TiO 2 film and a film thickness of about 45 nm ₂ The film has a 10-layer structure in which 5 layers are alternately stacked one by one. SiO ₂ The film is used as a low refractive index film, TiO ₂ The film is used as a high refractive index film. The reflectance of the fourth dielectric multilayer film 240 is about 95%.
10. Eighth embodiment
The nitride semiconductor laser element according to the eighth embodiment will be described while referring to differences from the nitride semiconductor laser element 1 according to the fifth embodiment.
FIG. 11 is a longitudinal sectional view of a nitride semiconductor laser element according to the eighth embodiment. FIG. 11 shows a longitudinal sectional view of the nitride-based semiconductor laser device 1 along the [0001] direction, similarly to the longitudinal sectional view of FIG. 2 in the first embodiment. 11 is the same as the longitudinal sectional view of the nitride-based semiconductor laser device 1 in FIG.
A third dielectric multilayer film 230 is formed on the light emitting surface 1Fa. The third dielectric multilayer film 230 is made of AlO. _X N _Y Film (X> Y) 231c, AlO _X N _Y Film (X <Y) 232c and Al ₂ O ₃ The film 233c has a structure in which the films are stacked in this order. AlO _X N _Y The refractive index of the film 231c is about 1.7, and AlO _X N _Y The refractive index of the film 232c is 1.9. AlO is an oxynitride film in which the composition ratio of oxygen is larger than the composition ratio of nitrogen _X N _Y The film (X> Y) 231c functions as a protective film for the light emitting surface 1Fa.
AlO _X N _Y Film 231c, AlO _X N _Y Film 232c and Al ₂ O ₃ The film thickness of the film 233c is about 30 nm, about 30 nm, and about 15 nm, respectively. The reflectance of the third dielectric multilayer film 230 is about 8%.
A fourth dielectric multilayer film 240 is formed on the rear surface 1Ba. The fourth dielectric multilayer film 240 is made of AlO. _X N _Y Film (X <Y) 241c, AlO _X N _Y The film (X> Y) 242c and the reflective film 243c are stacked in this order. AlO _X N _Y The refractive index of the film 241c is about 1.9, and AlO _X N _Y The refractive index of the film 242c is about 1.7. AlO which is an oxynitride film in which the composition ratio of nitrogen is larger than the composition ratio of oxygen _X N _Y The film 241c functions as a protective film for the rear surface 1Ba.
AlO _X N _Y Film 241c and AlO _X N _Y The film thickness of the film 242c is about 30 nm and about 30 nm, respectively. The reflective film 243c is made of SiO having a thickness of about 70 nm ₂ A TiO 2 film and a film thickness of about 45 nm ₂ The film has a 10-layer structure in which 5 layers are alternately stacked one by one. SiO ₂ The film is used as a low refractive index film, TiO ₂ The film is used as a high refractive index film. The reflectance of the fourth dielectric multilayer film 240 is about 95%.
11. Correspondence between each component of claim and each part of embodiment
Hereinafter, although the example of a response | compatibility with each component of a claim and each part of embodiment is demonstrated, this invention is not limited to the following example.
In the fifth to eighth embodiments, the optical waveguide WG is an example of an optical waveguide extending in the [0001] direction, the rear surface 1Ba is an example of one end surface composed of a (0001) plane, and the light emitting surface 1Fa. Is an example of the other end surface composed of the (000-1) plane.
Further, the light exit surface 1Fa and the rear surface 1Ba are examples of resonator surfaces, and an n-type cladding layer 103, an n-type carrier block layer 104, an n-type light guide layer 105, an active layer 106, a p-type light guide layer 107, p The nitride-based semiconductor layer formed by the type cap layer 108, the p-type cladding layer 109, and the p-type contact layer 110 is an example of a nitride-based semiconductor layer.
In the fifth embodiment, Al ₂ O ₃ The film 231 is an example of a second protective film containing oxygen as a constituent element, and the AlN film 241 is an example of a first protective film containing nitrogen as a constituent element. In the sixth embodiment, AlO _X N _Y The film (X> Y) 231a is an example of a second protective film containing oxygen as a constituent element. _X N _Y The film (X <Y) 241a is an example of a first protective film containing nitrogen as a constituent element. In the seventh embodiment, Al ₂ O ₃ The film 231b is an example of a second protective film containing oxygen as a constituent element, and the AlN film 241b is an example of a first protective film containing nitrogen as a constituent element. In the eighth embodiment, AlO _X N _Y The film (X> Y) 231c is an example of a second protective film containing oxygen as a constituent element. _X N _Y The film (X <Y) 241c is an example of a first protective film containing nitrogen as a constituent element.
As each constituent element in the claims, various other elements having configurations or functions described in the claims can be used.
12 Effects in the fifth to eighth embodiments
In the nitride-based semiconductor laser devices according to the fifth to eighth embodiments, a pair of optical waveguides in which one end face composed of the (0001) plane and the other end face composed of the (000-1) plane extend in the [0001] direction. The laser beam is emitted from one end surface and the other end surface.
Since one end face made of the (0001) plane is a group 13 element polar plane, it is easily covered with a group 13 element such as gallium. Here, since the first protective film containing nitrogen as a constituent element is provided on one end face, a surface level is generated at the interface between the one end face and the first protective film due to the bond between the group 13 element and oxygen. Is prevented. This prevents the laser light from being absorbed at the surface level at the interface between the one end face and the first protective film.
On the other hand, the other end surface composed of the (000-1) plane is a nitrogen polar surface and is therefore easily covered with nitrogen atoms. Therefore, the surface level due to the bond between the group 13 element and oxygen is unlikely to occur on the other end surface. A second protective film containing oxygen as a constituent element is provided on the other end surface. When the second protective film contains oxygen as a constituent element, the absorption of laser light is smaller than when nitrogen is contained as a constituent element. Therefore, absorption of laser light by the second protective film is suppressed.
As a result, the light emission efficiency of the laser light can be sufficiently improved.
Further, the intensity of the laser beam emitted from the other end surface is larger than the intensity of the laser beam emitted from the one end surface.
In this case, the other end surface composed of the (000-1) plane is the main light exit surface. Here, the one end face composed of the (0001) plane is easily covered with the group 13 element, and thus has a characteristic of being easily oxidized. On the other hand, the other end surface composed of the (000-1) plane is easily covered with nitrogen atoms, and therefore has a characteristic that it is difficult to be oxidized. As a result, deterioration of the main light exit surface due to oxidation is suppressed, and stable high output operation can be realized.
(A) Effects relating to a protective film covering the light emitting surface 1Fa and the rear surface 1Ba
In the fifth embodiment, Al is covered so as to cover the light emitting surface 1Fa. ₂ O ₃ A film 231 is formed. That is, the oxide film is formed on the (000-1) plane which is the N polar plane. The amount of laser light absorbed by the oxide film is smaller than the amount of laser light absorbed by the nitride film. Further, surface states are unlikely to occur at the interface between the (000-1) plane and the oxide film. Therefore, by forming an oxide film on the (000-1) plane, it becomes possible to sufficiently improve the light emission efficiency of the laser beam.
In the fifth embodiment, the AlN film 241 is formed so as to cover the rear surface 1Ba. That is, a nitride film is formed on the (0001) plane which is a Ga polar plane. In this case, generation of surface states due to the bonding of Ga atoms and O atoms at the interface between the rear surface 1Ba and the AlN film 241 is prevented. This prevents the laser light from being absorbed at the surface level at the interface between the rear surface 1Ba and the AlN film 241. Accordingly, it is possible to sufficiently improve the light emission efficiency of the laser light.
In the sixth embodiment, AlO, which is an oxide film in which the composition ratio of oxygen is larger than the composition ratio of nitrogen, is formed on the light exit surface 1Fa composed of the (000-1) plane. _X N _Y A film (X> Y) 231a is formed. Thereby, it is possible to sufficiently improve the light emission efficiency of the laser beam. In addition, on the rear surface 1Ba made of the (0001) plane, AlO which is a nitride film in which the nitrogen composition ratio is larger than the oxygen composition ratio. _X N _Y A film (X <Y) 241a is formed. Thereby, it is possible to sufficiently improve the light emission efficiency of the laser beam. Further, the refractive index of the first or second protective film can be easily changed by the composition ratio of nitrogen and oxygen, and the degree of freedom in designing the protective film can be increased.
In the seventh embodiment, Al, which is an oxide film, is formed on the light exit surface 1Fa composed of the (000-1) plane. ₂ O ₃ A film 231b is formed. Thereby, it is possible to sufficiently improve the light emission efficiency of the laser beam. An AlN film 241b, which is a nitride film, is formed on the rear surface 1Ba made of the (0001) plane. Thereby, it is possible to sufficiently improve the light emission efficiency of the laser beam.
In the eighth embodiment, AlO, which is an oxide film in which the composition ratio of oxygen is larger than the composition ratio of nitrogen, is formed on the light exit surface 1Fa composed of the (000-1) plane. _X N _Y A film (X> Y) 231c is formed. Thereby, it is possible to sufficiently improve the light emission efficiency of the laser beam. In addition, on the rear surface 1Ba made of the (0001) plane, AlO which is a nitride film in which the nitrogen composition ratio is larger than the oxygen composition ratio. _X N _Y A film (X <Y) 241c is formed. Thereby, it is possible to sufficiently improve the light emission efficiency of the laser beam. Further, the refractive index of the first or second protective film can be easily changed by the composition ratio of nitrogen and oxygen, and the degree of freedom in designing the protective film can be increased.
(B) Effect of (000-1) plane being light exit surface 1Fa
The (0001) plane, which is a Ga polar plane, has a characteristic that its surface is easily covered with Ga atoms and is easily oxidized. On the other hand, the (000-1) plane, which is an N polar plane, has a characteristic that its surface is easily covered with N atoms and is not easily oxidized.
In the present embodiment, the (000-1) plane is the light exit surface 1Fa. Thereby, it is suppressed that the light emission surface 1Fa is deteriorated by oxidation. Therefore, the laser characteristics of the nitride-based semiconductor laser device 1 can be stably maintained, and a stable high output operation can be realized.
Furthermore, in this embodiment, undoped In is used as the well layer 106b. _0.15 Ga _0.85 N is used. Thus, when the In composition ratio of the well layer 106b is extremely smaller than the Ga composition ratio, the unevenness of the active layer 106 on the light emitting surface 1Fa and the rear surface 1Ba is sufficiently suppressed.
As a result, it is possible to prevent the unevenness from becoming large even on the (000-1) plane where unevenness larger than that on the (0001) plane is likely to occur. As a result, the scattering of the laser light emitted from the light emitting surface 1Fa is reduced, and a good far-field image with little ripple is obtained.
13. Modified examples of the fifth to eighth embodiments
Next, modified examples of the fifth to eighth embodiments will be described. The differences between the nitride semiconductor laser element 1 of the above embodiment and the nitride semiconductor laser element 1 of this example are as follows.
In this example, the n-type cladding layer 103 and the p-type cladding layer 109 are made of Al. _0.03 Ga _0.97 N is used. The doping amount of Si into the n-type cladding layer 103 and the doping amount of Mg into the p-type cladding layer 109 are the same as in the above embodiment. The carrier concentration and thickness of the n-type cladding layer 103 and the p-type cladding layer 109 are the same as those in the above embodiment.
In this example, n-type Al is used as the n-type carrier block layer 104. _0.10 Ga _0.90 N is used, and n-type In as the n-type light guide layer 105 _0.05 Ga _0.95 N is used. The doping amount of Mg into the n-type carrier block layer 104 and the n-type light guide layer 105 is the same as that in the second embodiment. The carrier concentration and thickness of the n-type carrier block layer 104 and the n-type light guide layer 105 are the same as those in the above embodiment.
In this example, as the active layer 106, undoped In _0.25 Ga _0.75 Three barrier layers 106a made of N and undoped In _0.55 Ga _0.45 An active layer 106 having an MQW structure in which two well layers 106b made of N are alternately stacked is used. The thickness of each barrier layer 106a and each well layer 106b is the same as that in the above embodiment.
In this example, the p-type light guide layer 107 is p-type In. _0.05 Ga _0.95 N and p-type Al as the p-type cap layer 108 _0.10 Ga _0.90 N is used. The doping amount of Mg into the p-type light guide layer 107 and the p-type cap layer 108 is the same as that in the second embodiment. The carrier concentration and thickness of the p-type light guide layer 107 and the p-type cap layer 108 are the same as those in the above embodiment.
In this example, the In composition ratio contained in the active layer 106 is larger than the Ga composition ratio. In this case, the portion of the active layer 106 on the light emitting surface 1Fa is more easily oxidized. Therefore, by setting the (000-1) surface that is not easily oxidized as the light emission surface 1Fa, it is possible to suppress the light emission surface 1Fa from being deteriorated by oxidation. Therefore, the laser characteristics of the nitride-based semiconductor laser device 1 can be stably maintained, and a stable high output operation can be realized.
14 Other embodiments
(1) In the above embodiment, the oxide film in the first to fourth dielectric multilayer films 210, 220, 230, 240 is Al. ₂ O ₃ The nitride film is formed of AlN, and the oxynitride film is AlO. _X N _Y However, it is not limited to this. The oxide film in the first to fourth dielectric multilayer films 210, 220, 230, 240 is, for example, Al. ₂ O ₃ , SiO ₂ , ZrO ₂ , Ta ₂ O ₅ , HfO ₂ And AlSiO _X Any one or more of them may be formed. Here, X is a real number larger than zero. The nitride films in the first to fourth dielectric multilayer films 210, 220, 230, and 240 are, for example, AlN and Si. ₃ N ₄ May be formed by one or both of them. Furthermore, the oxynitride film is, for example, AlO. _X N _Y , SiO _X N _Y And TaO _X N _Y May be formed by one or more. Here, X and Y are real numbers greater than zero.
In the above embodiment, AlO _X N _Y The ratio of the composition ratio of nitrogen N to the composition ratio of oxygen O in the film (X <Y) 211a, 212b, 222b, 221c, 222c, 241a, 232b, 242b, 232c, 241c is, for example, 54 (%): 46 ( %).
In the above embodiment, the material for the low refractive index film is SiO. ₂ As a material for the high refractive index film, TiO ₂ However, it is not limited to this. MgF as material for low refractive index film ₂ Or Al ₂ O ₃ Other materials such as may be used. ZrO as a material for high refractive index film ₂ , Ta ₂ O ₅ , CeO ₂ , Y ₂ O ₃ , Nb ₂ O ₅ Or HfO ₂ Other materials such as may be used.
(2) When at least one of the light exit surface 1F and the rear surface 1B or at least one of the light exit surface 1Fa and the rear surface 1Ba is formed by cleavage, the main surface of the active layer 106 is (H, K, -HK, 0 ) Arbitrary plane orientations in the range of ± about 0.3 degrees from the plane. H and K are arbitrary integers, and at least one of H and K is an integer other than 0. Further, the light emitting surfaces 1F and 1Fa and the rear surfaces 1B and 1Ba formed by cleavage have arbitrary plane orientations in a range of ± about 0.3 degrees from the (0001) plane and the (000-1) plane, respectively. May be.
When the light emitting surfaces 1F and 1Fa and the rear surfaces 1B and 1Ba are formed by a method other than cleavage such as etching, polishing or selective growth, the light emitting surfaces 1F and 1Fa and the rear surfaces 1B and 1Ba are respectively (0001) surfaces. And any plane orientation in the range of ± about 25 degrees from the (000-1) plane. However, it is desirable that the light emitting surfaces 1F and 1Fa and the rear surfaces 1B and 1Ba are substantially perpendicular (90 ° ± about 5 °) to the main surface of the active layer 106.
(3) Substrate 101, n-type layer 102, n-type cladding layer 103, n-type carrier block layer 104, n-type light guide layer 105, active layer 106, p-type light guide layer 107, p-type cap layer 108, p-type For the cladding layer 109 and the p-type contact layer 110, a nitride of a group 13 element containing at least one of Ga, Al, In, Tl, and B can be used. Specifically, as a material for each layer, a nitride semiconductor composed of AlN, InN, BN, TlN, GaN, AlGaN, InGaN, InAlGaN, or a mixed crystal thereof can be used.
(4) Regarding the first, third, fifth, and seventh embodiments, when an AlN film is formed on the one end face (0001) surface as the first protective film in contact with the semiconductor, the AlN film is [0001]. It is preferable to form so as to have a high orientation in the direction. In this case, the thermal conductivity in the [0001] direction is increased, the temperature rise at the semiconductor interface can be suppressed, and the reliability can be improved.
In the case where the second AlN film is further formed as a layer other than the first protective film as in the fifth embodiment, the first AlN film and the second AlN are formed as the first layer. The orientation directions of the films do not necessarily coincide with each other, and it is not always necessary to increase the orientation as in the first AlN film of the first layer.

  INDUSTRIAL APPLICABILITY The present invention can be effectively used for optical pickup devices, display devices, light sources, etc., and their production.

1 is a longitudinal sectional view of a nitride based semiconductor laser device according to a first embodiment. 1 is a longitudinal sectional view of a nitride based semiconductor laser device according to a first embodiment. FIG. 3 is a partially enlarged cross-sectional view of the nitride-based semiconductor laser device of FIG. 2. FIG. 3 is a partially enlarged cross-sectional view of the nitride-based semiconductor laser device of FIG. 2. It is a longitudinal cross-sectional view of the nitride-type semiconductor laser element which concerns on 2nd Embodiment. It is a longitudinal cross-sectional view of the nitride-type semiconductor laser element which concerns on 3rd Embodiment. It is a longitudinal cross-sectional view of the nitride-type semiconductor laser element which concerns on 4th Embodiment. It is a longitudinal cross-sectional view of the nitride-type semiconductor laser element which concerns on 5th Embodiment. It is a longitudinal cross-sectional view of the nitride-based semiconductor laser element according to the sixth embodiment. It is a longitudinal cross-sectional view of the nitride-based semiconductor laser element according to the seventh embodiment. It is a longitudinal cross-sectional view of the nitride-type semiconductor laser element which concerns on 8th Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Nitride type | system | group semiconductor laser element 1B, 1Ba Back surface 1F, 1Fa Light emission surface 101 N-type GaN substrate 106 Active layer 106a Barrier layer 106b Well layer 210 1st dielectric multilayer 211, 223, 232, 241 AlN film 212, 221, 231 Al ₂ O ₃ film 220 Second dielectric multilayer film 222, 242 Reflective film 230 Third dielectric multilayer film 233 SiO ₂ film 240 Fourth dielectric multilayer film

Claims (6)

A nitride-based semiconductor layer having an optical waveguide extending in the [0001] direction and having one end face made of a (0001) face and the other end face made of a (000-1) face as a resonator face;
A first protective film provided on the one end face of the nitride-based semiconductor layer and containing nitrogen as a constituent element;
A nitride-based semiconductor laser device comprising: a second protective film provided on the other end surface of the nitride-based semiconductor layer and containing oxygen as a constituent element. 2. The nitride-based semiconductor laser device according to claim 1, wherein the intensity of the laser beam emitted from the one end surface is greater than the intensity of the laser beam emitted from the other end surface. The part of the one end face in the optical waveguide and the part of the other end face in the optical waveguide each have an uneven shape,
3. The nitride-based semiconductor laser device according to claim 2, wherein a depth of the concave-convex recess on the one end surface is smaller than a depth of the concave-convex recess on the other end surface. 2. The nitride-based semiconductor laser device according to claim 1, wherein the intensity of the laser beam emitted from the other end surface is greater than the intensity of the laser beam emitted from the one end surface.   The nitride-based semiconductor laser device according to claim 1, wherein the first protective film further includes oxygen as a constituent element, and a composition ratio of nitrogen is larger than a composition ratio of oxygen. 5. The nitride-based semiconductor laser device according to claim 1, wherein the second protective film further includes nitrogen as a constituent element, and a composition ratio of oxygen is larger than a composition ratio of nitrogen.

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