JP2005340625A - Nitride semiconductor laser device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitride semiconductor laser device of large dynamic range capable of significantly reducing kink for both reliability at high output and usability at low output. <P>SOLUTION: The nitride semiconductor laser device comprises a laminated semiconductor layer in which n-type semiconductor layers 11-14, active layer 15, and p-type semiconductor layers 16-19 of nitride are laminated, and an out-going side laser mirror and reflection-side laser mirror positioned on the end face almost vertical to a waveguide region in which an active layer is sandwiched between the n-type semiconductor layer and p-type semiconductor layer. The active layer can emit light within the wavelength band including violet-blue to green, with the reflectivity of the laser mirror on the front side being 60% or less. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a nitride semiconductor laser element, and more particularly to a structure for reducing fluctuation (kink) of light emission output during laser oscillation. For example, a light source for an optical head of an optical disk device, an LD display, a medical light source, It is used for bio light sources, printing light sources, optical modules, and the like.

  A GaN-based nitride laser diode (LD) is considered promising as a light source for reading / writing information on an optical disk at a high density, for example. For example, a short wavelength LD having an emission wavelength of 400 nm band (380 nm to 420 nm including blue-violet) is promising as a pickup light source for next generation optical disks and next generation DVDs. In addition, a long wavelength LD having an emission wavelength of 440 nm band (420 nm to 550 nm including blue to green) is promising as an LD display for displaying images, a medical light source, a bio light source, a printing light source, an optical module, and the like. An LD array can be used as the LD.

In general, Patent Document 1 discloses that a dielectric multilayer film is provided as a laser mirror of an LD resonator.
JP 2003-88691 A

  The inventor of the present application, for example, in commercializing a nitride semiconductor laser element of the 400 nm band or the 440 nm band as described above, the relationship between the current I and the light emission output L (IL characteristics), particularly the light emission output generated during laser oscillation. The wavelength dependence of the kink was investigated. As a result, as shown in FIG. 8, it has been found that the kink gradually increases as the wavelength increases. When such a kink is large, there is no problem when the semiconductor laser element is operated by continuous oscillation, but there is a problem when the semiconductor laser element is operated by pulse oscillation or when it is operated at high speed by direct modulation.

  Furthermore, as a result of repeated experiments on the kinks of the 440 nm band nitride semiconductor laser element, the inventor of the present application has found that the kinks depend on the magnitude of the light emission output and the reflectance of the laser mirror.

  The present invention has been made based on the above knowledge, and it is possible to significantly reduce kinks, and a nitride semiconductor having a large dynamic range that can achieve both high output reliability and ease of use at low output. An object is to provide a laser element.

According to a first aspect of the nitride semiconductor laser device of the present invention, a first semiconductor layer of a first conductivity type made of a nitride semiconductor, an active layer, a stacked semiconductor layer in which a second conductivity type semiconductor layer is stacked, and the active layer A front-side laser mirror and a rear-side laser mirror located on an end surface substantially perpendicular to the waveguide region of the laser beam comprising the first conductive type semiconductor layer and the second conductive type semiconductor layer sandwiching the active layer The active layer is formed of In _x Al _y Ga _1-xy N (0.05 ≦ x ≦ 0.25, 0 ≦ y ≦ 0.95, 0.05). ≦ x + y ≦ 1), and the reflectance of the front side laser mirror is 60% or less. Here, the front-side laser mirror is formed with a laminated film in which a first translucent film and a second translucent film having different refractive indexes with respect to the laser beam are laminated on one end face of the waveguide region. And a structure in which a single layer film made of a first light-transmitting film is formed as a protective film on one end face of the waveguide region. When using a multilayer laser mirror film on the front side, ZrO ₂ film as the first transparent film, the SiO ₂ film used as the second transparent film, the first transparent film and the second magnetic This can be realized by laminating 1.5 to 2.5 pairs of optical films. When a single layer film is used for the front-side laser mirror, the first light-transmitting film is an Al ₂ O ₃ film, an Nb ₂ O ₅ film, an HfO _x film, an MgO film, a Ta ₂ O ₅ film, an SiON film, By using any one of the AlO _x N _y film and the GaO _x film, it is possible to realize the reflectance of the front side laser mirror to be 20% or less.

According to a second aspect of the nitride semiconductor laser element of the present invention, there is provided a first semiconductor layer made of a nitride semiconductor, an active layer, a stacked semiconductor layer in which a second conductive semiconductor layer is stacked, and the active layer. A front-side laser mirror and a rear-side laser mirror located on an end surface substantially perpendicular to the waveguide region of the laser beam comprising the first conductive type semiconductor layer and the second conductive type semiconductor layer sandwiching the active layer a nitride semiconductor laser device having a preparative, the active _{layer, in x Al y Ga 1-} x-y N (0.05 ≦ x ≦ 0.25,0 ≦ y ≦ 0.95,0. 05 ≦ x + y ≦ 1), and the laser mirror on the front side includes an Al ₂ O ₃ film, an Nb ₂ O ₅ film, an HfO _x film, an MgO film, a Ta ₂ O ₅ film, an SiON film, and an AlO _x N _y film. , a single-layer film made from one of GaO _x layer is said electrically Characterized by comprising formed on one end surface of the road area.

In each of the above embodiments, the rear-side laser mirror is realized by laminating a first light-transmitting film and a second light-transmitting film having different refractive indexes with respect to laser light on one end face of the waveguide region. It is possible, and it is preferable that the reflectance of the rear side laser mirror be 90% or more. In this case, ZrO ₂ film as the first transparent film, the SiO ₂ film used as the second transparent film, the first transparent film and the second transparent film 4.5 to 6 It can be realized by stacking 5 pairs.

  Moreover, in each said aspect, an active layer can light-emit within the range of the wavelength range containing blue purple-green, and has an energy band gap of 420 nm or more and 550 nm or less in conversion of the wavelength of light. is there.

  According to the first aspect of the nitride semiconductor laser device of the present invention, in the nitride semiconductor laser device capable of emitting light in the wavelength range including blue-violet to green, the front-side laser mirror serves as a laser beam. A first light-transmitting film and a second light-transmitting film having different refractive indexes are laminated on one end face of the waveguide region, or a single-layer film of the first light-transmitting film is formed on one end of the waveguide region. By forming it on the end face and making the reflectance of the laser mirror on the front side 60% or less, preferably 20% or less, it becomes possible to greatly reduce kinks, reliability at high output and low output It can have a large dynamic range that can balance the ease of use.

According to the second aspect of the nitride semiconductor laser element of the present invention, in the nitride semiconductor laser element capable of emitting light in the wavelength range including blue-violet to green, as the front side laser mirror, Al ₂ O By using a single layer film composed of any one of _three films, Nb ₂ O ₅ film, HfO _x film, MgO film, Ta ₂ O ₅ film, SiON film, AlO _x N _y film, and GaO _x film, Can be drastically reduced, and a large dynamic range that can achieve both high output reliability and low output ease of use can be provided.

<First Embodiment>
The nitride semiconductor laser device according to the first embodiment is substantially perpendicular to a laminated semiconductor layer including an active layer having an energy band gap of 420 nm or more and 550 nm or less in terms of light wavelength, and a waveguide region of the laser light. It has a front side laser mirror (hereinafter referred to as an emission side mirror) and a rear side laser mirror (hereinafter referred to as a reflection side mirror) located on the end face. Here, the active layer has a composition capable of emitting light such as blue, blue-green, and green within a range of 420 nm to 550 nm. The output side mirror has a reflectance of 60% or less, more preferably 20% or less, and the reflection side mirror has a reflectance of 60% or more, more preferably 90% or more. Yes.

  FIG. 1A is an example of a cross-sectional structure that is a part of the nitride semiconductor laser device of the first embodiment and is cut in a direction perpendicular to the resonance direction of laser light (a direction parallel to the resonance surface). Is shown schematically. In this example, the first conductivity type is n-type and the second conductivity type is p-type.

  In FIG. 1A, a first conductivity type (n-type) semiconductor layer, an active (Act) layer 15 and a second conductivity type (p-type) semiconductor layer each made of a nitride semiconductor are formed on a substrate (not shown). ) Is formed on the stacked semiconductor layer.

  The n-type semiconductor layer includes an n-side contact layer (n-contact layer) 11, a crack prevention layer (Crack-Barrier layer) 12, an n-side cladding layer (n-Clad layer) 13, an n-side light guide layer (n-contact layer). Guide layer) 14 is laminated. The p-type semiconductor layer includes a p-side electron confinement layer (p-Cap layer) 16, a p-side light guide layer (p-Guide layer) 17, a p-side cladding layer (p-Clad layer) 18, a p-side contact layer ( p-Contact layer) 19 is laminated.

  The n-side contact layer 11 may be partially used when a GaN-based substrate is used to grow the stacked semiconductor layer. Further, a part of the p-side contact layer 19, the p-side cladding layer 18 and the p-side light guide layer 17 is etched so as to form a ridge stripe having a stripe width of about 2 μm. Due to the ridge shape, the light emission of the Act layer 15 is concentrated on the lower part of the ridge, the transverse mode is easily unified, and the threshold value is easily lowered.

  The nitride semiconductor laser device of this embodiment has a separated light confinement (SCH) structure in which an Act layer 15 is sandwiched between an n-Guide layer 14, a p-Cap layer 16, and a p-Guide layer 17. This SCH structure constitutes an optical waveguide by providing light guide layers having a band gap larger than that of the Act layer 15 on both sides of the Act layer 15. Furthermore, the n-Clad layer 13 and the p-Clad layer 18 are provided on both sides of the SCH structure. The n-Clad layer 13 and the p-Clad layer 18 are provided with a nitride semiconductor layer having a low refractive index so as to have an optical confinement effect and a carrier confinement effect. Moreover, it is good also as a structure which has a stress buffer layer between each said layer.

The general formula of the nitride semiconductor forming each semiconductor layer of the nitride semiconductor laser element is In _x Al _y Ga _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1). The n-type nitride semiconductor contains any one or more of Si, Ge, O, etc. as an n-type impurity. A p-type nitride semiconductor contains Mg, Zn or the like as a p-type impurity.

The Act layer 15 _{is In x Al y Ga 1-x} -y N (0.05 ≦ x ≦ 0.25,0 ≦ y ≦ 0.95,0.05 ≦ x + y ≦ 1), contains the In By controlling the amount, light emission from 420 nm to 470 nm and further to 550 nm is possible. The Act layer 15 has a multiple quantum well structure or a single quantum well structure, and when formed with a multiple quantum well structure, the light emission efficiency is improved. A multi-quantum well structure can start with a barrier layer and end with a well layer, start with a barrier layer and end with a barrier layer, start with a well layer and end with a barrier layer, or start with a well layer and end with a well layer Good. Preferably, the structure starts with the barrier layer and repeats the pair of the well layer and the barrier layer 2 to 8 times and ends with the barrier layer. A structure in which a pair of a well layer and a barrier layer is repeated 2 to 3 times is preferable for reducing the threshold current and improving the life characteristics.

  FIG. 1B schematically shows an example of a cross-sectional structure of the Act layer 15 in FIG. The Act layer 15 in this example includes a first barrier layer 151, a first well layer 152, a middle barrier layer 153, a second well layer 154, It has a multiple quantum well structure in which a final barrier layer 155 is stacked.

  Further, although not shown in FIGS. 1 (a) and 1 (b), the waveguide layer of laser light composed of the Act layer 15 and an n-type semiconductor layer and a p-type semiconductor layer sandwiching the Act layer 15 is substantially omitted. An emission side mirror and a reflection side mirror are formed on the vertical end face, and each laser mirror forms a laser resonator together with the waveguide region. When monitoring the laser light output, the reflection side mirror for taking out the monitor light is called a monitor side mirror.

  The waveguide region is a region that propagates light and is formed in a planar stripe shape. Here, the propagated light is amplified by the resonance of the laser resonator, and laser oscillation occurs. Further, it is preferable that the cross-sectional shape of the current confinement region is a protrusion (ridge shape) so that current can be efficiently injected into the waveguide region.

Each of the laser mirrors has a case where at least two types of translucent films having different refractive indexes with respect to laser light are arranged in a laminated state on the one end surface side of the waveguide region in a predetermined number of pairs, and one type of translucent film. A photo film (for example, any one of an Al ₂ O ₃ film, an Nb ₂ O ₅ film, and an HfO _x film) may be disposed. In this case, each translucent film has a thickness of m / 4n (n: integer of 1 or more, m: odd number) of the wavelength of the laser beam inside thereof, and one end face (crystal cleavage plane) of the waveguide region The translucent film in contact with () also protects optical damage of the crystal cleavage plane, and also has a role of improving the light emission output and improving the lifetime.

  Further, although not shown in FIGS. 1A and 1B, a first electrode (p electrode, positive electrode) is formed so as to make ohmic contact with the surface of the p-side contact layer 19, and the n-side A second electrode (n electrode, negative electrode) is formed so as to be electrically connected to contact layer 11.

  When the p electrode and the waveguide region are viewed from above, the planar arrangement relationship between them is that, as shown in FIG. 7A, one end of the p electrode 21 is one end surface (crystal cleavage surface) of the waveguide region. ) A structure corresponding to A and a structure in which one end of the p-electrode 21 is about 0.1 to 5 μm away from one end face (crystal cleavage face) of the waveguide region as shown in FIG. 7B. . The structure in which one end of the p electrode 21 coincides with one end surface A of the waveguide region is adopted when Au is not used for the p electrode 21 and the COD (Catastrophic Optical Damage) level is improved. In this case, even if Au is used for the p-electrode 21, the COD level is improved when the film thickness is thin (about 10 to 300 nm).

  On the other hand, the structure in which one end of the p electrode 21 is separated from the one end surface A of the waveguide region is not restricted by using Au for the p electrode 21. In this case, in the waveguide region, the portion between one end of the p-electrode 21 and the one end surface A of the waveguide region is not directly injected, so that it becomes an absorption region, and the band gap decreases due to heat generation. Crystal breakage easily occurs due to COD. However, the structure shown in FIG. 7B is problematic because one end of the p-electrode 21 is close to the one end face (crystal cleavage face) of the waveguide region (about 0.1 to 5 μm apart) as described above. However, characteristics equivalent to the structure shown in FIG.

Table 1 shows the film thickness of each layer of the nitride semiconductor laser element shown in FIGS. 1A and 1B, the minimum value (Minimum), the standard value of the mixed crystal ratio _{x of In} or the mixed crystal ratio _y of Al. An example of the maximum value (Maximum) is shown. (Table 1)
Film thickness 混 Mixed crystal ratio (In _x or Al _y )
Minimum Maximum ‖ Minimum Maximum
―――――――――――――――――――――――――――――――――――――
n-Contact 2 μm 4 μm 7.5 μm ‖ y = 0.010 y = 0.02 y = 0.045
Crack-Barrier 90 nm 150 nm 250 nm ‖ x = 0.014 x = 0.03 x = 0.06
n-Clad 0.8 μm 1.3 μm 2.2 μm ‖ y = 0.035 y = 0.059 y = 0.100
n-Guide 200 nm 315 nm 520 nm ‖ − − −
1st Barrier 20 nm 40 nm 150 nm ‖ x = 0.02 x = 0.04 x = 0.075
1st Well 1.7 nm 3 nm 6.7 nm ‖ x = 0.06 x = 0.10 x = 0.18
Middle Barrier 8 nm 14 nm 24 nm ‖ x = 0.02 x = 0.04 x = 0.075
2nd Well 1.7 nm 3 nm 6.7 nm ‖ x = 0.06 x = 0.10 x = 0.18
Last Barrier 20 nm 40 nm 200 nm ‖ x = 0.02 x = 0.04 x = 0.075
p-Cap 5.3 nm 10 nm 18 nm ‖ y = 0.14 y = 0.25 y = 0.45
p-Guide 200 nm 315 nm 520 nm ‖ − − −
p-Clad 270 nm 450 nm 750 nm ‖ y = 0.027 y = 0.046 y = 0.100
p-Contact 6.7 nm 15 nm 30 nm ‖ − − −
In Table 1, the Crack-Barrier layer, the 1st Barrier layer, the 1st Well layer, the Middle Barrier layer, the 2nd Well layer and the Last Barrier layer are layers containing In _x . n-the Contact layer, n-Clad layer, p-Cap layer and p-Clad layer is a layer containing Al _y. The n-Guide layer, p-Guide layer and p-Contact layer are GaN layers.

The Crack-Barrier layer has a film thickness of 130 to 170 nm and an In mixed crystal ratio _x of 0.02 to 0.04. The 1st Barrier layer and the Last Barrier layer have a film thickness of 30 to 100 nm and an In mixed crystal ratio _x of 0.03 to 0.05. The Middle Barrier layer has a film thickness of 12 to 16 nm and an In mixed crystal ratio _x of 0.03 to 0.05. The 1st Well layer and the 2nd Well layer have a film thickness of 2.5 to 4.5 nm and an In mixed crystal ratio _x of 0.09 to 0.12.

The n-Contact layer has a thickness of 3 to 5 μm and an Al mixed crystal ratio _y of 0.015 to 0.03. The n-Clad layer has a film thickness of 1.2 to 1.5 μm and an Al mixed crystal ratio _y of 0.050 to 0.070. The p-Cap layer has a thickness of 8 to 12 nm and an Al mixed crystal ratio _y of 0.20 to 0.30. The p-Clad layer has a film thickness of 400 to 500 nm and an Al mixed crystal ratio _y of 0.040 to 0.070. The n-Guide layer and the p-Guide layer have a thickness of 300 to 350 nm, and the p-Contact layer has a thickness of 10 to 20 nm.

  FIGS. 2A and 2B schematically show two examples of the cross-sectional structure of the laser mirror of the nitride semiconductor laser element shown in FIGS. 1A and 1B.

The laser mirror shown in FIG. 2A has a first light-transmitting film 1 having a first refractive index n1 with respect to the laser light in order from the one end face side of the waveguide region, and a refractive index higher than that. A second light-transmitting film 2 having a relatively low second refractive index n2 is laminated. In this case, depending on the material of the translucent film to be used, one pair consisting of the first translucent film 1 and the second translucent film 2 or only 1.5 to 6.5 pairs. For example, the layers are alternately stacked by a sputtering apparatus. As the first translucent film 1, a ZrO ₂ (zirconium oxide) film, an Al ₂ O ₃ (alumina) film, an Nb ₂ O ₅ (niobium oxide) film, an HfO _x film, an MgO film, and a Ta ₂ O ₅ film are used. , SiON film, AlO _x N _y film, GaO _x film, and the like, and the second light transmissive film 2 includes SiO ₂ (silicon oxide) film.

  With such a structure, reflection and transmission of laser light are repeated at the interface between the translucent films 1 and 2, so that the reflectance approaches 100% as the number of layers increases, and the reflectance decreases as the number of layers decreases. . In the laser mirror shown in FIG. 2B, a single layer film made of the first translucent film 1 as described above is formed on one end face of the waveguide region.

  In the present embodiment, the reflectance of the exit side mirror is 75% or less, preferably 60% or less, more preferably 20% or less, and the reflectance of the reflection side mirror is 75% or more, preferably It is configured to be 85% or more, more preferably 90% or more.

Table 2 shows that the first light transmissive film 1 of the laser mirror shown in FIG. 2 is one of a ZrO ₂ film, an Nb ₂ O ₅ film, and an Al ₂ O ₃ film, and a second light transmissive film 2. In the case of using the SiO ₂ film as the material, the material and film thickness of the first light-transmitting film 1 and the second light-transmitting film 2, the first light-transmitting film and the second light-transmitting film, An example of the result of examining the relationship between the number of pairs consisting of (Pair number) and the reflectance of the laser mirror is shown.

(Table 2)
Type Material Film thickness Number of Pairs Reflectivity ―――――――――――――――――――――――――――――――――
(A) SiO ₂ / ZrO ₂ 73 nm / 49 nm 6.5 Pair 98.5%
(B) SiO ₂ / ZrO ₂ 73 nm / 49 nm 5.5 Pair 97%
(C) SiO ₂ / ZrO ₂ 73 nm / 49 nm 4.5 Pair 93%
(D) SiO ₂ / ZrO ₂ 73 nm / 49 nm 3.5 Pair 85%
(E) SiO ₂ / ZrO ₂ 73 nm / 49 nm 2.5 Pair 71%
(F) SiO ₂ / ZrO ₂ 73 nm / 49 nm 1.5 Pair 49%
(G) Nb ₂ O ₅ 89 nm monolayer 18%
(H) Al ₂ O ₃ 138 nm monolayer 18%
(I) Al ₂ O ₃ 167 nm monolayer 11%
(J) Al ₂ O ₃ about 69 nm monolayer 0%
(K) HfO ₂ about 52 nm monolayer 11%
As can be seen from Table 2, as an example, when a ZrO ₂ film (49 nm) is used as the first translucent film 1 and an SiO ₂ film (73 nm) is used as the second translucent film 2, By setting the Pair number in the range of 4.5 to 6.5, the reflectance of the laser mirror can be set to 90% or more (for example, 93 to 98.5%), and the Pair number is set to 3. By setting the reflectance to 5, the reflectance of the laser mirror is set to 85%, and the number of pairs is set in the range of 1.5 to 2.5, thereby setting the reflectance to 75% or less (for example, 49 to 71%). It is possible.

As another example, when a single layer film of Nb ₂ O ₅ film (89 nm) is used as the first light transmissive film 1, the reflectance of the laser mirror can be set to 18%. Even if the film thickness of the Nb ₂ O ₅ film is increased, the reflectance of the laser mirror cannot be changed so much. An SiO ₂ film (73 nm) may be added as the _second light transmissive film 2.

As yet another example, when an Al ₂ O ₃ film (138 nm) single-layer film is used as the first light-transmitting film 1, the reflectance of the laser mirror can be set to 18%. An SiO ₂ film (73 nm) may be added as the _second light transmissive film 2. When the film thickness of the Al ₂ O ₃ film is changed, the reflectance of the laser mirror can be changed from 18% to 0%. For example, when a single layer film of an Al ₂ O ₃ film (167 nm) is used as the first light-transmitting film 1, the reflectance of the laser mirror can be set to 11%. Further, when a single layer film of an Al ₂ O ₃ film (about 69 nm) is used as the first translucent film 1, the reflectance of the laser mirror can be set to 0%. As yet another example, when a single-layer film of HfO ₂ film (about 52 nm) is used as the first light-transmitting film 1, the reflectance of the laser mirror can be set to 11%. The single-layer film of the first light transmissive film 1 can be used as a protective film for the emission end face.

  Table 3 shows the light-transmitting film material and Pair number of the emission-side mirror of the nitride semiconductor laser element shown in FIGS. 1A and 1B, and the light-transmitting film material and Pair number of the monitor-side mirror. Several examples suitable for realization are shown.

(Table 3)
Type Outgoing mirror material Number of pairs Monitor side mirror material Number of pairs ――――――――――――――――――――――――――――――――――
(1) SiO ₂ / ZrO ₂ 3.5 Pair SiO ₂ / ZrO ₂ 4.5 Pair
(2) SiO ₂ / ZrO ₂ 2.5 Pair SiO ₂ / ZrO ₂ 4.5 Pair
(3) SiO ₂ / ZrO ₂ 2.5 Pair SiO ₂ / ZrO ₂ 5.5 Pair
(4) SiO ₂ / ZrO ₂ 2.5 Pair SiO ₂ / ZrO ₂ 6.5 Pair
(5) Al ₂ O ₃ single layer SiO ₂ / ZrO ₂ 4.5 Pair
(6) Al ₂ O ₃ single layer SiO ₂ / ZrO ₂ 5.5 Pair
(7) Al ₂ O ₃ single layer SiO ₂ / ZrO ₂ 6.5 Pair
As can be seen from Table 3, by setting the ZrO ₂ film / SiO ₂ film pair as the reflection side mirror in the range of 4.5 to 6.5 pairs, the reflectance is 90% or more (for example, 93 to 98. 5%).

In this case, the reflectance can be set to 60% or less (for example, 49%) by setting the pair of the ZrO ₂ film and the SiO ₂ film to 1.5 pairs as the output side mirror.

Further, by using a single layer film of Nb ₂ O ₅ film (or Al ₂ O ₃ film) as the exit side mirror, the reflectance can be set to 20% or less (for example, 18%). An SiO ₂ film (73 nm) may be added as the _second light transmissive film 2.

  FIG. 3A shows an example of the result of measuring the IL characteristics of the nitride semiconductor laser element in the 440 nm band shown in FIGS. 1A and 1B by changing the reflectance of the output side mirror. FIG. 3B is a characteristic diagram illustrating a part of FIG.

  As can be seen from FIGS. 3A and 3B, when the reflectivity of the output side mirror is 85%, the threshold current is about 38 mA, and the light emission output rises to about 10 mW with a current of about 70 mA. When the reflectance of the output side mirror is 71%, the threshold current is about 40 mA, and the light emission output rises to about 25 mW with a current of about 80 mA. When the reflectance of the output side mirror is 49%, the threshold current is about 52 mA, and the light emission output rises to about 50 mW with a current of about 100 mA. When the reflectance of the output side mirror is 18%, the threshold current is about 60 mA, and the light emission output rises to about 60 mW with a current of about 100 mA.

FIG. 3C shows the IL characteristics when the reflectivity of the exit side mirror is set to 11% and 0% for the 440 nm band nitride semiconductor laser device shown in FIGS. 1A and 1B. An example of the results is shown. When a single-layer film of HfO ₂ film (about 52 nm) is used as the output end face protective film (the output side mirror has a reflectance of 11%), the light emission output rises sharply at a current of about 130 mA. Further, when a single layer film of an Al ₂ O ₃ film (about 69 nm) is used as the output end face protective film (the reflectivity of the output side mirror is 0%), the light emission output gradually increases as the current increases.

  FIG. 4 shows an example (solid line) of the measurement result of the relationship between the reflectivity of the exit side mirror and the kink for the nitride semiconductor laser element in the 440 nm band shown in FIGS. An example of the result of measuring the relationship between the reflectivity of the exit mirror and the kink for the nitride semiconductor laser element (dotted line) is shown in comparison.

  As shown by the solid line in FIG. 4, as the reflectivity of the exit side mirror is lowered from 85% to 18% (the light emission output is increased), the kink is greatly reduced from about 180 to about 120 (150%). It was found that the kink is reduced to about 150 or less when the reflectance of the exit side mirror is 60% or less, and the kink is reduced to about 120 when the reflectance of the exit side mirror is 20% or less. In other words, it has been found that when the reflectance of the output side mirror of the nitride semiconductor laser element in the 440 nm band is reduced to 60% or less, the wavelength dependence of the kink is smaller than that of the conventional one.

  As described above, according to the nitride semiconductor laser element of the 440 nm band of the present embodiment, it becomes possible to greatly reduce the kink by reducing the reflectance of the emission side mirror (increasing the light emission output), It can have a large dynamic range that can achieve both high output reliability and low output ease of use. Therefore, for example, it is applied to a semiconductor laser element mounted on an optical head (pickup) of an optical disk device and directly modulated by a pulse current, or directly modulated at a high speed by a pulse current to perform high-speed scanning of an LD display. Suitable for use.

  Incidentally, as shown by the dotted line in FIG. 4, in the 400 nm band nitride semiconductor laser device, the kink is reduced from about 115 to about 105 when the reflectance of the output side mirror is lowered from 85% to 18%. . In other words, in the 400 nm band nitride semiconductor laser element, the ratio of the kink depending on the reflectance of the output side mirror is lower than that in the 440 nm band nitride semiconductor laser element.

  As described above, in order to reduce the reflectivity of the exit side mirror of the nitride semiconductor laser element of the 440 nm band according to the present embodiment to a predetermined value or less, the number of pairs of the translucent multilayer film of the exit side mirror is reduced. It is effective to use a translucent single layer film for the output side mirror, or to select the material and film thickness of the translucent film.

  Hereinafter, each component of the nitride semiconductor laser device shown in FIG. 1A will be described in detail.

The substrate for growing the nitride semiconductor layer is preferably a single substrate made of only a single semiconductor, but the single substrate is made of a different material (sapphire, SiC, Si, spinel, SiO ₂₎ different from the semiconductor. It is also possible to use a conductive or insulating substrate that is entirely or partially provided with SiN, etc.). The semiconductor of the single substrate is a compound semiconductor, such as a III-V group compound semiconductor or a II-VI group compound semiconductor. Specific examples include a GaN-based compound semiconductor, a GaAs-based compound semiconductor, and a ZnO-based compound semiconductor. GaN-based compound semiconductors include GaN, AlN, which are compounds of Group III elements B, Ga, Al, In, etc. and Group V elements, N, AlGaN, which is a ternary or quaternary mixed crystal compound, InAlGaN and the like include those containing n-type impurities and p-type impurities.

  If a nitride semiconductor substrate is used as the substrate, problems such as lattice mismatch with the nitride semiconductor layer do not occur. When a conductive substrate having a first main surface and a second main surface is used, a semiconductor layer and an electrode are sequentially formed on the first main surface side, and an electrode is formed on the second main surface side. The nitride semiconductor laser device having the counter electrode structure can be realized, a large current can be input, and high output oscillation is possible.

  There are various methods for manufacturing a nitride semiconductor substrate. For example, after growing a nitride semiconductor layer with reduced dislocations on a heterogeneous substrate of a material different from that of a nitride semiconductor by an ELOG (epitaxial lateral growth) method, a selective growth method, etc., the heterogeneous substrate used as the growth substrate is grown. After removing, the single nitride semiconductor substrate is taken out. As a method for removing the foreign substrate, polishing, grinding, etching, laser irradiation, or the like is used. Further, a bulk single crystal formed by a hydrothermal synthesis method in which crystals are grown in a supercritical fluid, or a high pressure method or a flux method may be used as the nitride semiconductor substrate. Examples of the vapor deposition method include MOCVD (metal organic chemical vapor deposition) method and HVPE (halide vapor phase epitaxial growth) method.

  A specific example of a method for manufacturing a nitride semiconductor substrate will be described. A buffer layer made of a nitride semiconductor is grown on a heterogeneous substrate such as sapphire, SiC, or GaAs. At this time, the growth temperature of the buffer layer is set to 900 ° C. or lower. Next, a nitride semiconductor is grown in a thick film of 50 μm or more on a heterogeneous substrate. Thereafter, the nitride semiconductor substrate can be obtained by removing the heterogeneous substrate by polishing, electromagnetic wave irradiation (excimer laser irradiation, etc.), CMP (chemical mechanical polishing), or the like. In this case, a nitride semiconductor substrate having a full width at half maximum of a (0002) diffraction X-ray rocking curve by a biaxial crystal method of 100 arcsec or less, preferably 60 arcsec or less can be obtained.

  Here, the growth surface of the nitride semiconductor substrate manufactured as described above is referred to as a first main surface, and the exposed surface side exposed by removing the heterogeneous substrate is referred to as a second main surface. The first main surface of the nitride semiconductor substrate may have a (000-1) plane in addition to a crystal growth plane such as a C plane, an A plane, or an M plane. The second main surface of the nitride semiconductor substrate is preferably a (000-1) plane, and may be provided with a (0001) plane in addition. In the present specification, a bar (-) in parentheses representing an area index represents a bar to be added on the back number. The outer peripheral shape of the nitride semiconductor substrate is not particularly limited, and may be a wafer shape, a rectangular shape, or the like.

An example of a nitride semiconductor substrate is one in which dislocations are periodically distributed in the plane, for example, one in which low dislocation density regions and high dislocation density regions are alternately formed in stripes by using the ELOG method. Since such a nitride semiconductor substrate works to relieve stress generated inside, it is possible to stack nitride semiconductor elements with a film thickness of 5 μm or more without forming a stress relaxation layer on the substrate. Become. As a specific example of the ELOG method, there is a method in which a nitride semiconductor is regrown after forming irregularities on a substrate. The case where the low dislocation density region and the high dislocation density region are formed in a stripe shape includes not only the case where the low dislocation density region and the high dislocation density region are formed continuously, but also the case where the low dislocation density region and the high dislocation density region are formed in a broken line shape (intermittently). In the low dislocation density region, the number of dislocations per unit area is 1 × 10 ⁷ / cm ² or less, preferably 1 × 10 ⁶ / cm ² or less. The high dislocation density region may be a region having a dislocation density higher than that of the low dislocation density region. These dislocations are measured by CL observation, TEM observation, or the like. A semiconductor laser device having a waveguide region in which a ridge is formed above a low dislocation region having a dislocation density of 1 × 10 ⁶ / cm ² or less, preferably 5 × 10 ⁵ / cm ² or less can improve life characteristics. it can.

  As another example of the nitride semiconductor substrate, a first region containing a first n-type impurity and an n-type impurity different from the first region are included on the first main surface. And a second region. In order to form the first region and the second region containing different n-type impurities, the first main surface of the nitride semiconductor substrate is doped with the n-type impurities during the production of the nitride semiconductor substrate. The first region is formed by growing the nitride semiconductor while the second region is formed by ion-implanting an n-type impurity different from the first region into the surface other than the first region. As another example of the method of forming the second region, after forming a recess on the surface of the nitride semiconductor substrate, the recess is regrown while doping an n-type impurity different from that of the first region.

  Further, an off-angle may be formed on the surface of the nitride semiconductor substrate, or a newly exposed surface may be formed by grinding by etching or the like. The off angle is not less than 0.02 ° and not more than 90 °, preferably not less than 0.05 ° and not more than 5 °.

The impurity concentration of the n-type impurity contained in the nitride semiconductor substrate is 1 × 10 ¹⁷ cm ⁻³ to 1 × 10 ²⁰ cm ⁻³ . The thickness of the nitride semiconductor substrate is 50 μm or more and 1 mm or less, preferably 50 μm or more and 500 μm or less. Within this range, the cleavage can be performed with good reproducibility after the nitride semiconductor laser element is formed on the wafer. Moreover, if the thickness of the nitride semiconductor substrate is less than 50 μm, handling in the device process becomes difficult.

  The first main surface of the nitride semiconductor substrate can be formed with any uneven portion by subjecting the surface of the substrate to wet etching, dry etching, or CMP treatment. Examples of dry etching include RIE (reactive ion etching), RIBE (reactive ion beam etching), ECR (electron cyclotron resonance), ICP (high frequency inductively coupled plasma), FIB (focused ion beam), and the like. A nitride semiconductor substrate having a surface with partially different crystal growth surfaces as described above is preferable because it eliminates stress and strain generated in the substrate. Specifically, the first main surface is the (0001) plane. In addition, the (000-1) plane, (11-20) plane, (10-15) plane, (10-14) plane, (11-24) plane, which are crystal growth planes different from the (0001) plane, It is what you have.

  The second main surface of the nitride semiconductor substrate has at least two or more different crystal growth surfaces. Specifically, the (000-1) plane, the (0001) plane, the (11-20) plane, (10 It is preferable to have a −15) plane, a (10-14) plane, a (11-24) plane, and the like. With such a nitride semiconductor substrate, the nitride semiconductor element grown on the substrate suppresses stress applied to the element and can withstand damage during cleavage.

  The n-side cladding layer 13 and the p-side cladding layer 17 may have a single layer structure, a two-layer structure, or a superlattice structure including two layers having different composition ratios. The total film thickness of the n-side cladding layer 13 is 0.4 to 10 μm, and the total film thickness of the p-side cladding layer 17 is 0.2 to 8 μm, and the forward voltage (Vf) is within this range. It is preferable for reducing. The average Al composition of the n-side cladding layer 13 and the p-side cladding layer 17 is 0.02 to 0.1. This value is preferable for suppressing the occurrence of cracks and obtaining a difference in refractive index from the laser optical waveguide.

The doping amount of the n-type impurity is 1 × 10 ¹⁷ / cm ^{3 to} 5 × 10 ¹⁹ / cm ³ . When the n-type impurity is doped in this range, the resistivity can be lowered and the crystallinity is not impaired. The doping amount of the p-type impurity is 1 × 10 ¹⁹ / cm ³ to 1 × 10 ²¹ / cm ³ . When the p-type impurity is doped in this range, the crystallinity is not impaired.

Examples of the n-type impurity include Si, Ge, Sn, S, O, Ti, Zr, and Cd. Examples of the p-type impurity include Be, Zn, Mn, Ca, and Sr in addition to Mg. The impurity concentration is preferably in the range of 5 × 10 ¹⁶ / cm ^{3 to} 1 × 10 ²¹ / cm ³ . When the impurity concentration is higher than 1 × 10 ²¹ / cm ³ , the crystallinity of the nitride semiconductor layer is deteriorated and the output tends to decrease. The same applies to modulation doping.

On the nitride semiconductor substrate, the n-side cladding layer 13 can also be grown via an underlayer. The underlayer is Al _a Ga _1-a N (0 ≦ a ≦ 0.5). Thereby, dislocations (threading dislocations and the like) and pits generated on the surface of the nitride semiconductor layer can be reduced. The underlayer has a single layer structure or a multilayer laminated structure. If the n-side cladding layer 13 is a single layer, the general formula is Al _x Ga _1-x N (0 ≦ x ≦ 0.2), and the film thickness is 0.5 to 5 μm. In order to grow in multiple layers, the superlattice structure has a first layer Al _x Ga _1-x N (0 ≦ x ≦ 0.1) and a second layer Al _y Ga _1-y N (0 .01 ≦ y ≦ 1).

  When forming the n-electrode on the second main surface of the nitride semiconductor substrate, it is formed on the second main surface by CVD, sputtering, vapor deposition or the like. The n electrode has at least one selected from the group consisting of Ti, Ni, Au, Pt, Al, Pd, W, Rh, Ag, Mo, V, and Hf. When the n-electrode has a multilayer structure, it is preferable that the uppermost layer of the multilayer structure is Pt or Au because heat dissipation from the electrode can be improved. By selecting these materials as the materials of the electrodes formed on the second main surface of the nitride semiconductor substrate, the ohmic characteristics between the substrate and the electrode made of a nitride semiconductor can be obtained. Further, the adhesion between the substrate made of a nitride semiconductor and the electrode is good, and it has the effect of suppressing the electrode from peeling off in the cleavage step for forming a bar or chip from the wafer. The thickness of the n electrode is 1000 nm or less, preferably 600 nm or less. When the n-electrode has a multilayer structure, specifically, the first layer is made of V, Ti, Mo, W, Hf, or the like. Here, the thickness of the first layer is 50 nm or less. If the first layer is W, it is preferable that the thickness is 30 nm or less because good ohmic characteristics can be obtained. If the first layer is V, the heat resistance is improved, which is preferable. Here, favorable ohmic characteristics can be obtained by setting the film thickness of V to 5 nm to 30 nm, preferably 7 nm to 20 nm.

  If the n-electrode is Ti / Al, the film thickness is 1000 nm or less, for example, the film thickness is 10 nm / 500 nm. If the n-electrode is laminated in the order of Ti / Pt / Au from the second main surface side of the nitride semiconductor substrate, the film thickness is 6 nm / 100 nm / 300 nm. If the n-electrode is Ti / Mo / Pt / Au from the second main surface side of the nitride semiconductor substrate, for example, Ti (6 nm) / Mo (50 nm) / Pt (100 nm) / Au (210 nm). If the n electrode is Ti / Hf / Pt / Au, for example, Ti (6 nm) / Hf (6 nm) / Pt (100 nm) / Au (300 nm), and Ti / Mo / Ti / Pt / Au, Ti (6 nm) / Mo (50 nm) / Ti (50 nm) / Pt (100 nm) / Au (210 nm) can be laminated in this order. If the n electrode is W / Pt / Au, W / Al / W / Au, etc., the above characteristics are exhibited. As another example of the multilayer structure of the n-electrode, Hf / Al, Ti / W / Pt / Au, Ti / Pd / Pt / Au, Pd / Pt / Au, Ti from the second main surface side of the nitride semiconductor substrate / W / Ti / Pt / Au, Mo / Pt / Au, Mo / Ti / Pt / Au, W / Pt / Au, V / Pt / Au, V / Mo / Pt / Au, V / W / Pt / Au Cr / Pt / Au, Cr / Mo / Pt / Au, Cr / W / Pt / Au, and the like. After forming the n-electrode 22, annealing may be performed at 300 ° C. or higher.

  The n electrode is formed in a rectangular shape. The n-electrode is patterned on the second main surface side of the nitride semiconductor substrate in a range excluding a region that becomes a scribe line in a scribe process for forming the nitride semiconductor substrate in a subsequent process into a bar. Furthermore, when a metallized electrode (which can be omitted) is formed on the n-electrode in the same pattern shape, scribing is facilitated and cleavage is improved. As metallized electrodes, Ti-Pt-Au- (Au / Sn), Ti-Pt-Au- (Au / Si), Ti-Pt-Au- (Au / Ge), Ti-Pt-Au-In, Au / Sn, In, Au / Si, Au / Ge, or the like can be used.

  Further, a step may be formed on the second main surface of the nitride semiconductor substrate. By forming the step, if the second main surface is the (000-1) plane, an inclined surface other than the (000-1) plane can be exposed. For example, a plane index or the like that means a plane other than the (000-1) plane is not specified as one plane, and is a (10-15), (10-14), (11-24) plane, or the like. The inclined surface other than the (000-1) surface is preferably 0.5% or more of the surface area of the surface exhibiting n polarity. More preferably, it is 1% or more and 20% or less.

  Here, the step is an interface step of 0.1 μm or more, and the step shape is a taper shape or a reverse taper shape. Further, the planar pattern of the steps has a convex portion and / or a concave portion selected from a stripe shape, a lattice shape, an island shape, a circular shape, a polygonal shape, a rectangular shape, a comb shape, and a mesh shape. For example, if a circular convex part is formed, the diameter width of the circular convex part shall be 5 micrometers or more. Further, it is preferable that the recess groove has a width of at least 3 μm because the electrode does not peel off. In order to expose an inclined surface other than the (000-1) plane, the off angle may be formed in a range of 0.2 to 90 °. Since the second main surface of the nitride semiconductor substrate is a surface on which an n-electrode is formed, the ohmic characteristics can be improved by having a surface other than the (000-1) surface and the (000-1) surface. . Thereby, a highly reliable nitride semiconductor laser device can be obtained.

  In carrying out the present invention, the nitride semiconductor substrate and the nitride semiconductor layer are formed by MOVPE (metal organic chemical vapor deposition), MOCVD, HVPE (halide vapor deposition), MBE (molecular beam vapor deposition), etc. All known methods for growing nitride semiconductors can be applied.

  Hereinafter, although several examples of the nitride semiconductor laser device of the present invention will be shown, the present invention is not limited to these. The same reference numerals are given to the same parts throughout the drawings of the embodiments, and detailed description thereof is omitted.

[Example 1]
FIG. 5 schematically shows a cross-sectional structure of the 440 nm band nitride semiconductor laser device of the first embodiment. Here, a counter electrode structure is shown in which a pair of electrodes are formed separately on the upper and lower surfaces of the chip.

  The 440 nm band nitride semiconductor laser device of Example 1 has a ridge waveguide structure including an active layer having an energy band gap of 420 nm or more and 550 nm or less in terms of light wavelength, and an end face substantially perpendicular to the waveguide region And an output side mirror and a reflection side mirror.

  This semiconductor laser device has a structure in which an n-contact layer 11, a crack-barrier layer 12, an n-contact layer are formed on a first main surface of a conductive nitride semiconductor substrate (for example, a GaN substrate) 10 as a nitride semiconductor layer. A -Clad layer 13, an n-Guide layer 14, an Act layer 15, a p-Cap layer 16, a p-Guide layer 17, a p-Clad layer 18, and a p-Contact layer 19 are formed by layer growth. The n-Contact layer 11, Crack-Barrier layer 12, n-Clad layer 13, and n-Guide layer 14 are doped with n-type impurities, and include a p-Cap layer 16, a p-Guide layer 17, and a p-Clad layer 18. The p-contact layer 19 is doped with p-type impurities. The Act layer 15 is doped with n-type impurities in this example.

  On the upper surface portions of the p-Contact layer 19 and the p-Cladp layer 18, a current confinement region (ridge portion) having a stripe-like plane and a projecting (ridge-like) cross section is formed. A resonance surface is formed on an end surface substantially perpendicular to the waveguide region. The ridge may be formed by digging down to a part of the p-Guide layer 17.

Then, a buried insulating film (for example, a ZrO ₂ film having a thickness of 50 nm) 20 covering the side surface of the ridge portion and the surface of the p-Cladp layer 18 is in ohmic contact with the upper surface of the ridge portion, and the surface of the ridge portion and the buried surface are buried. A p-electrode 21 covering a part of the insulating film, a protective insulating film (for example, a SiO ₂ film having a thickness of 500 nm) 24, and a p-pad electrode 23 are formed. The protective insulating film 24 is formed on each of the p-type semiconductor layers 18, 17, 16, the active layer 15, and the n-type semiconductor layers 14, 13, 12, 11 from the side end portion of the p-electrode 21. It is formed so as to cover the side surface. Pad electrode 23 is formed so as to cover from p electrode 21 to a part of protective insulating film 24. Further, the second main surface (back surface side) of the GaN substrate 10 is lapped and polished, and adjusted to a predetermined thickness (thinly for improving heat dissipation), and then an n-electrode 22 is formed.

  In Example 1, the Act layer 15 has an SCH structure in which an n-Guide layer 14 and a p-Guide 17 are formed on both sides, and an n-Clad layer 13 and a p-Clad layer 18 are formed on both sides of the SCH structure. Have. As these n-Clad layer 13 and p-Clad layer 18, a nitride semiconductor layer having a low refractive index is provided to provide a light confinement function and a carrier confinement effect. In addition, it is good also as a structure which has a stress buffer layer between each layer.

  For example, as shown in FIG. 1B, the Act layer 15 has a multiple quantum well structure in which a 1st Barrier layer 151, a 1st Well layer 152, a Middle Barrier layer 153, a 2nd Well layer 154, and a Last Barrier layer 155 are stacked. Have.

Table 4 shows an example of the thickness of each layer of the nitride semiconductor laser element shown in FIG. 5, the mixed crystal ratio _{x of In,} or the mixed crystal ratio _y of Al.

(Table 4)
Film thickness 混 Mixed crystal ratio (In _x or Al _y )
―――――――――――――――――――――――――――――
n-Contact 4 μm ‖ y = 0.02
Crack-Barrier 150 nm ‖ x = 0.03
n-Clad 1.3 μm ‖ y = 0.059
n-Guide 315 nm ‖ −
1st Barrier 40 nm ‖ x = 0.035
1st Well 3 nm ‖ x = 0.10
Middle Barrier 14 nm ‖ x = 0.035
2nd Well 3 nm ‖ x = 0.10
Last Barrier 40 nm ‖ x = 0.035
p-Cap 10 nm ‖ y = 0.25
p-Guide 315 nm ‖ −
p-Clad 450 nm ‖ y = 0.046
p-Contact 15 nm ‖ −
In Table 4, Crack-Barrier layer, 1st Barrier layer, 1st Well layer, Middle Barrier layer, 2nd Well layer and Last Barrier layer are layers containing In _x , n-Contact layer, n-Clad layer, p-Cap layer and p-Clad layer is a layer containing Al _y. The n-Guide layer, p-Guide layer and p-Contact layer are GaN layers.

The Crack-Barrier layer has a thickness of 150 nm and an In mixed crystal ratio _x of 0.03. The 1st Barrier layer and the Last Barrier layer have a film thickness of 40 nm and an In mixed crystal ratio _x of 0.035. The Middle Barrier layer has a film thickness of 14 nm and an In mixed crystal ratio _x of 0.035. The 1st Well layer and the 2nd Well layer have a film thickness of 3 nm and an In mixed crystal ratio _x of 0.10.

The n-Contact layer has a film thickness of 4 μm and an Al mixed crystal ratio _y of 0.02. The n-Clad layer has a film thickness of 1.3 μm and an Al mixed crystal ratio _y of 0.059. The p-Cap layer has a thickness of 10 nm and an Al mixed crystal ratio _y of 0.25. The p-Clad layer has a thickness of 450 nm and an Al mixed crystal ratio _y of 0.046. The n-Guide layer and the p-Guide layer have a film thickness of 315 nm, and the p-Contact layer has a film thickness of 15 nm.

An example of the cross-sectional structure of the laser mirror of the nitride semiconductor laser device shown in FIG. 5 is as described above with reference to FIG. 2 (a) or 2 (b). In the first embodiment, the output side mirror has a first light-transmitting film 1 having a first refractive index n1 with respect to the laser light in order from the one end face side of the waveguide region, and a refractive index higher than that. 1.5 pairs of the second light-transmitting films 2 having a low second refractive index n2 are laminated. Here, as shown in the type (F) in Table 2, the first translucent film 1 is a ZrO ₂ film (49 nm), and the second translucent film 2 is an SiO ₂ film (73 nm). ing. In this case, as described above with reference to Table 2, the reflectance of the exit side mirror is 49%. On the other hand, the reflection side mirror is formed by laminating only 4.5 pairs of the first translucent film 1 and the second translucent film 2 in order from the other end surface side of the waveguide region. Yes. Here, a ZrO ₂ film (49 nm) is formed as the first light-transmitting film 1, and a SiO ₂ film (73 nm) is formed as the _second light-transmitting film 2. In this case, as described above with reference to Table 2, the reflectance of the reflection side mirror is 93%.

  According to the first embodiment, as described above with reference to FIGS. 3A and 3B, the threshold current is 440 nm having an IL characteristic that rises to a light emission output of about 50 mW with a current of about 52 mA and about 100 mA. A band nitride semiconductor laser device is obtained. And as mentioned above with reference to FIG. 4, the effect that a kink reduces to about 140 is acquired.

[Example 2]
Example 2 of the nitride semiconductor laser device is the same as Example 1 described above except that the mixed crystal ratio of the n-Clad layer 13 and the p-Clad layer 18, the n-Guide layer 14, the p-Cap layer 16, and the p-Guide. The nitride semiconductor laser element is formed under the same conditions except that the thicknesses of the layer 17 and the p-Clad layer 18 are changed.

Table 5 shows an example of the thickness of each layer of the nitride semiconductor laser element shown in FIG. 5, the mixed crystal ratio _{x of In,} or the mixed crystal ratio _y of Al.

(Table 5)
Film thickness 混 Mixed crystal ratio (In _x or Al _y )
―――――――――――――――――――――――――――――
n-Contact 4 μm ‖ y = 0.02
Crack-Barrier 150 nm‖ X = 0.03
n-Clad 1.3 μm‖ y = 0.062
n-Guide 330 nm‖ −
1st Barrier 40 nm‖ X = 0.035
1st Well 3 nm‖ X = 0.10
Middle Barrier 14 nm ‖ X = 0.035
2nd Well 3 nm ‖ X = 0.10
Last Barrier 40 nm ‖ X = 0.035
p-Cap 8 nm ‖ y = 0.25
p-Guide 330 nm ‖ −
p-Clad 500 nm‖ y = 0.055
p-Contact 15 nm ‖ −
As shown in Table 5, the Crack-Barrier layer has a thickness of 150 nm and an In mixed crystal ratio _x of 0.03. The 1st Barrier layer and the Last Barrier layer have a film thickness of 40 nm and an In mixed crystal ratio _x of 0.035. The Middle Barrier layer has a film thickness of 14 nm and an In mixed crystal ratio _x of 0.035. The 1st Well layer and the 2nd Well layer have a film thickness of 3 nm and an In mixed crystal ratio _x of 0.10. The n-Contact layer has a film thickness of 4 μm and an Al mixed crystal ratio _y of 0.02. The n-Clad layer has a film thickness of 1.3 μm and an Al mixed crystal ratio _y of 0.062. The p-Cap layer has a thickness of 8 nm and an Al mixed crystal ratio _y of 0.25. The p-Clad layer has a thickness of 500 nm and an Al mixed crystal ratio _y of 0.055. The n-Guide layer and the p-Guide layer have a thickness of 330 nm, and the p-Contact layer has a thickness of 15 nm.

  Also according to the second embodiment, a nitride semiconductor laser device having substantially the same characteristics as the first embodiment can be obtained.

[Example 3]
In Example 3, an Al ₂ O ₃ film (89 nm) as shown in the type (H) in Table 2 is used as the first translucent film 1 of the output side mirror in Example 1 or Example 2 described above. Other than that, a nitride semiconductor laser element was formed under the same conditions (the second translucent film 2 was not used). In this case, as described above with reference to Table 2, the reflectance of the exit side mirror is 18%.

  According to the third embodiment, the output side mirror has a lower reflectance and a higher light emission output than the first embodiment, and the threshold current is about 60 mA as described above with reference to FIGS. 3 (a) and 3 (b). Thus, a 440 nm band nitride semiconductor laser device having IL characteristics that rises to a light emission output of about 60 mW with a current of about 100 mA can be obtained. And as mentioned above with reference to FIG. 4, the effect that a kink reduces greatly to about 120 is acquired.

In Example 3, the first translucent film 1 of the output side mirror may be modified such that a SiO ₂ film (73 nm) is laminated as the second translucent film 2.

[Method of Manufacturing Semiconductor Laser Element of Example 1]
(Substrate) In a MOCVD reactor, a sapphire or GaAs substrate is placed and the temperature is set to 500 ° C. Next, a buffer layer made of GaN is grown to a thickness of 20 nm using triethylgallium (TEG) and / or trimethylgallium (TMG) and ammonia (NH ₃ ). After growing the buffer layer, the temperature is set to 1050 ° C., and an underlying layer made of GaN is grown to a thickness of 4 μm. After growing the underlayer, the wafer is taken out of the reaction vessel, a striped photomask is formed on the surface of the underlayer, and a SiO 2 having a stripe width of 10 to 300 μm and a stripe interval (window) of 5 to 300 μm is formed by a CVD apparatus. _A protective film made of ₂ is formed.

After forming the protective film, the wafer is transferred to an HVPE (hydride vapor phase epitaxy) apparatus, Ga metal, HCl gas, and ammonia are used as raw materials, and GaN is doped with Si and / or O as n-type impurities. The resulting nitride semiconductor is grown to a thickness of 400 μm. As described above, when a GaN thick film of 100 μm or more is grown while growing a nitride semiconductor on the protective film by the HVPE method, crystal defects are reduced by two orders of magnitude or more. Then, the GaN substrate 10 is obtained by peeling the dissimilar substrate or the like by polishing, grinding, CMP, laser irradiation or the like. This GaN substrate 10 has a film thickness of about 400 μm, and has a dislocation density of 5 × 10 ⁶ / cm ² or less at least under a region where a waveguide is to be formed.

(N-Contact layer 11) When a GaN layer is grown on the substrate, an intermediate layer 11a is further grown, and TMA (trimethylaluminum), TEG and / or TMG, ammonia, and silane gas are grown at 1050 ° C. as the uppermost layer. Then, an n-Contact layer 11 made of Al _0.02 Ga _0.98 N doped with Si is grown.

(Crack-Barrier layer 12) Next, the temperature is set to 800 ° C., and TEG and / or TMG, TMI, ammonia, silane gas is used as a source gas, and a crack-barrier layer 12 made of In _0.03 Ga _0.97 N doped with Si. Is grown to a thickness of 150 nm.

(N-Clad layer 13) Next, an n-Clad layer 13 made of Al _0.059 Ga _0.941 N doped with Si using TMA, TEG and / or TMG, ammonia, and silane gas at 1050 ° C. with a film thickness of 1.3 μm. Grow to become. The n-Clad layer 13 can also have a superlattice structure.

(N-Guide Layer 14) Next, the silane gas is stopped, and an n-Guide layer 14 made of undoped GaN is grown at 1050 ° C. to a thickness of 315 nm.

(Act layer 15) Next, the Act layer 15 is grown using TEG and / or TMG, TMI, ammonia, and silane gas. At this time, the temperature is maintained at 800 ° C., and first, a 1st barrier layer 151 made of In _0.035 Ga _0.965 N doped with Si is grown to a film thickness of 40 nm. Subsequently, at the same temperature, a 1st Well layer 152 made of In _0.10 Ga _0.90 N is grown to a thickness of 3 nm. Such barrier layers and well layers are alternately stacked twice. At this time, after the 1st Well layer 152 is grown, a Middle Barrier layer 153 made of In _0.035 Ga _0.965 N doped with Si is grown to a thickness of 14 nm. Subsequently, a 2nd Well layer 154 made of In _0.10 Ga _0.90 N is grown to a thickness of 3 nm. Thereafter, an Act layer 15 having a multiple quantum well structure with a total film thickness of 100 nm is obtained by growing a Last Barrier layer 155 made of In _0.035 Ga _0.965 N doped with Si so as to have a film thickness of 40 nm.

(P-Cap layer 16) Next, the temperature was raised to 1050 ° C., and TEG and / or TMG, TMA, ammonia, Cp ₂ Mg (cyclopentadienyl magnesium) was used, and Mg doped Al _0.25 Ga _0.75 N A p-Cap layer 16 is grown to a thickness of 10 nm. The p-Cap layer 16 can be omitted.

(P-Guide layer 17) Subsequently, Cp ₂ Mg and TMA were stopped, and a p-Guide layer 17 made of undoped GaN having a band gap energy smaller than that of the above-described p-Cap layer 16 at 1050 ° C. was set to 315 nm. Grow to become.

(P-Clad layer 18) Subsequently, at 1050 ° C., a layer made of Al _0.046 Ga _0.954 N doped with Mg is grown to a thickness of 2.5 nm, then Cp ₂ Mg and TMA are stopped, and from undoped GaN Is grown by a thickness of 2.5 nm. Such a pair is grown 90 times to grow a p-Clad layer 18 having a superlattice structure with a total film thickness of 450 nm.

(P-Contact 19) Finally, at 1050 ° C., the p-Contact layer 19 made of GaN doped with Mg is grown on the p-Clad layer 18 to a thickness of 15 nm.

  After the reaction is completed, the temperature is lowered to room temperature, and the wafer is annealed in a reaction vessel at 700 ° C. in a nitrogen atmosphere to further reduce the resistance of the p-type semiconductor layer. After annealing, the wafer is removed from the reaction vessel.

Next, the n-side semiconductor layer is exposed by etching for the purpose of stress relaxation. Although the exposed surface of the n-side semiconductor layer is not particularly limited, for example, a part of the contact layer 11 is exposed. At this time, the etching is performed by a RIE method using a chlorine-based gas such as Cl ₂ , CCl ₄ , SiCl ₄ , and BCl ₃ . Then, a protective film (not shown) made of SiO ₂ or the like is formed in a stripe shape on the surface of the uppermost p-Contact 19. This protective film has a pattern shape for forming a ridge portion which is a stripe-shaped current confinement region, and the stripe-shaped ridge portion is formed by etching by the RIE method using this protective film as a mask. In the case of forming a ridge stripe, in particular, by forming a layer above the p-type semiconductor layer containing Al above the Act layer 15 into a ridge shape, the light emission of the Act layer 15 is concentrated at the bottom of the ridge, and the transverse mode is It is easy to unify, and the threshold value tends to decrease. The width of the ridge is 1.0 μm to 50.0 μm. The length of the ridge portion in the stripe direction is 300 μm to 1000 μm. When the laser beam is set to a single mode, the width of the ridge portion is preferably 1.0 μm to 2.0 μm. If the width of the ridge portion is 10 μm or more, an output of 200 mW or more is possible. The height of the ridge portion may be in a range where the p-Guide layer 17 is exposed. The reason for this is that when a large current is applied, the current rapidly spreads laterally below the ridge portion, and therefore the etching depth for forming the ridge portion is preferably up to the p-Guide layer 17.

Next, the buried insulating film 20 is covered to protect the side surfaces of the ridge portion and the surface of the p-Clad layer 18. The buried insulating film 20 has a refractive index smaller than that of the nitride semiconductor layer and is selected from insulating materials. Specific examples include ZrO ₂ , SiO ₂ , and other oxides such as V, Nb, Hf, and Ta.

  Next, a p-electrode 21 is formed on the surface of the p-contact layer 19. Preferably, the p-electrode 21 is formed in a multilayer structure on part of the p-contact layer 19 and the buried insulating film 20. At this time, when the p electrode 21 has a two-layer structure made of, for example, Ni and Au, first, Ni is formed on the p-contact layer 19 with a film thickness of 5 nm to 20 nm, and then Au is 50 nm to It is formed with a film thickness of 300 nm. Further, when the p-electrode 21 has a three-layer structure, there are Ni / Au / Pt, Ni / Au / Pd, etc., and Ni and Au may have the same film thickness as the two-layer structure. And Pd is 50 nm to 500 nm. When the p electrode 21 is formed, as shown in FIGS. 7A and 7B, the p electrode 21 is formed so that one end of the p electrode coincides with one end surface of the waveguide region, and the one end of the p electrode is formed. In some cases, it is formed a little away from one end face of the waveguide region.

  After the p-electrode 21 is formed as described above, ohmic annealing is performed. As detailed conditions, the annealing temperature is 300 ° C. or higher, preferably 500 ° C. or higher. The atmosphere in which annealing is performed is a condition containing nitrogen and / or oxygen.

Thereafter, a protective insulating film 24 made of SiO _{2 is} formed to a thickness of 0.5 μm on a part (side end portion) of the p electrode 21 and the buried insulating film 20 and on the side surface of the semiconductor layer exposed in the previous step. Thus, it is formed by sputtering film formation.

  Next, the p pad electrode 23 is formed on the p electrode 21 and a part of the protective insulating film 24. The p pad electrode 23 is preferably a laminated body made of a metal such as Ni, Ti, Au, Pt, Pd, and W. For example, the p pad electrode 23 is made of W / Pd / Au or Ni / Ti / Au from the p electrode 21 side. It is formed continuously in order. The film thickness of the p-pad electrode 23 is not particularly limited, but the film thickness of the final Au layer is 100 nm or more. The p-pad electrode 23 is formed with an area larger than the surface area of the p-electrode 21, improving heat dissipation and facilitating wire bonding. Further, the p-pad electrode 23 is formed thicker than the p-electrode 21 and has a role of preventing the p-electrode 21 from peeling off. Thereafter, an n-electrode 22 made of V (10 nm) / Pt (200 nm) / Au (300 nm) is formed on a part or the whole of the second main surface of the GaN substrate 10.

  Next, the wafer on which the p electrode 21, the n electrode 22, and the p pad electrode 23 are formed as described above is cleaved in a bar shape in a direction perpendicular to the ridge stripe. Here, the resonance plane is an M plane (1-100 plane, a plane corresponding to a side surface of a hexagonal columnar crystal) or an A plane (11-20 plane). Examples of the cleavage method for dividing the wafer into bars include blade break, roller break, or press break.

  In this case, it is preferable to form the resonance surface with a high yield by performing the wafer dividing process in two stages. First, a cleavage assisting groove is formed in advance by scribing from the first main surface side or the second main surface side of the wafer-like GaN substrate 10. The cleavage assist groove has a depth of 10 μm, a width of 50 μm in the direction parallel to the resonance surface, and a width of 15 μm in the vertical direction, and is formed on the entire surface of the wafer or on both ends of the wafer to form bars. Preferably, the cleavage assisting grooves are formed at intervals in the form of broken lines in the cleavage direction for forming the bar. Thereby, bending of the cleavage direction can be suppressed. Further, by forming cleavage assist grooves in advance on the first main surface and / or the second main surface of the GaN substrate 10, the wafer can be easily cleaved into a bar shape. By having the cleavage assist groove on the second main surface of the GaN substrate 10, there is an effect of preventing the n-electrode 22 formed on the second main surface (back surface) from peeling off.

A resonator having a resonator length of 300 to 1000 μm is fabricated by cleaving the wafer into a bar shape from the surface on which the n-electrode 22 of the GaN substrate 10 is formed using the above-described cleavage assist line, and then the reflecting surface side of the resonator And / or a laser mirror is formed on the exit surface side. The laser mirror is a dielectric laminated film made of SiO ₂ , ZrO ₂ , TiO ₂ , Al ₂ O ₃ , Nb ₂ O ₅ or the like. The laser mirror is preferably formed on the reflection surface side and the emission surface side of the resonance surface. A resonant surface formed by cleavage can be formed with good reproducibility. As the laser mirror on the emission surface side, any one of an Al ₂ O ₃ film, an Nb ₂ O ₅ film, an HfO _x film, an MgO film, a Ta ₂ O ₅ film, an SiON film, an AlO _x N _y film, and a GaO _x film is used. When a single-layer film consisting of one is used, the reflectance can be lowered.

  Further, as described above, the nitride semiconductor substrate cleaved in a bar shape and formed with the laser mirror is divided into chips parallel to the ridge stripe (parallel to the p-electrode 21). The shape of the chip is rectangular, and the width of the rectangular resonance surface is 500 μm or less, preferably 400 μm or less. Here, the left and right corners on the resonance surface side of the nitride semiconductor laser element have concave grooves. The concave groove has a depth of 10 μm and a width of 30 μm in the direction parallel to the resonance surface and 10 μm in the vertical direction.

When the n-electrode 22 side of the nitride semiconductor laser element chip manufactured in this way was placed on a heat sink, wire bonding connection was made to the p-electrode 21, and laser oscillation was attempted at room temperature, the oscillation wavelength was 435 to 465 nm, the threshold value Good continuous oscillation is exhibited at room temperature at a current density of 2.9 kA / cm ² . Furthermore, even if the resonance surface is formed by cleavage as described above, there is no cleavage flaw, the light output is 50 mW in continuous operation (CW), the lifetime is 10,000 hours, and the lifetime is 10,000 hours. Can be manufactured with good reproducibility.

  The nitride semiconductor laser element having such characteristics can be used as a light source for optical modules, medical use, biotechnology, printing, exposure, and the like.

  The p pad electrode 23 may be simply electrically connected to the p electrode 21. The pad electrode 23 is thicker than the p-electrode 20 to prevent the p-electrode 21 from being peeled off, and the surface area is larger than that of the p-electrode 21. In addition to facilitating wire bonding connection, it is possible to improve heat dissipation by increasing the bonding area when connecting the p-electrode 21 side to a heat sink such as a heat sink or a submount.

[Example 4]
FIG. 6 schematically shows an example of a cross-sectional structure of the nitride semiconductor laser device according to the fourth embodiment.

  The nitride semiconductor laser device of FIG. 6 has an external electrode or the like on the p pad electrode 23 in order to make the p electrode 21 side the mounting surface to the heat sink, as compared with the nitride semiconductor laser device of the first embodiment. The difference is that it has a face-down structure in which a metallized layer (bump) (not shown) for connection is formed, and the others are the same. Here, the p-pad electrode 23 may be used in combination with the metallized layer. The metallized layer is made of a material such as Ag, Au, Sn, In, Bi, Cu, or Zn. By using the GaN substrate 10 as the substrate, a nitride semiconductor laser element having a face-down structure can be provided with good reproducibility. According to the fourth embodiment, the heat dissipation is good and the reliability is improved.

[Example 5]
In the fifth embodiment of the nitride semiconductor laser device, the n electrode 22 is disposed on the first main surface side of the GaN substrate 10 (that is, the p electrode 21 and the n electrode 22 are disposed on the same surface side of the chip). It is. In this case, as compared with the first embodiment described above, etching is performed so that a part of the n-contact layer 11 is exposed, an n electrode 22 is formed on a part of the exposed upper surface, and a protective insulating film is formed on the remaining part of the exposed upper surface. Is forming. After the p-electrode 21 and the n-electrode 22 are formed on the same surface side, the wafer is transferred to a polishing apparatus, and the back surface of the GaN substrate 10 is lapped using a diamond abrasive so that the thickness of the substrate is 100 μm. Thereafter, the back surface of the substrate is mirror-finished by 1 μm polishing with a fine abrasive. Thus, by reducing the thickness of the substrate to 100 μm or less, the heat dissipation of the nitride semiconductor laser element is enhanced. Thereafter, the polished surface side of the GaN substrate 10 is scribed and cleaved in a bar shape in a direction perpendicular to the ridge stripe, and a resonator having a resonator length of 650 μm is produced on the cleaved surface. Further, a light-transmitting laminated film made of SiO ₂ and ZrO ₂ is formed on the resonator surface, and finally the bar is cut in a direction parallel to the ridge stripe to form an LD chip.

  Thus, the LD chip having the same-surface electrode structure is placed on the heat sink in a face-up state (the GaN substrate 10 faces the heat sink), and wires made of gold wires are respectively connected to the p electrode 21 and the n electrode 22. Connect by bonding. Since the position at the time of wire bonding is a position away from the position of the ridge stripe while avoiding the position directly above the ridge stripe, no impact is applied to the ridge portion, so that the crystal of the ridge portion is not broken.

[Other Examples]
As another embodiment, there is a modification in which the p-electrode 21 is formed only on the p-contact layer 19 in each of the embodiments described above. According to this structure, since the buried insulating film 20 and the p electrode 21 are not in close contact, the p electrode 21 is not peeled off at the interface between the buried insulating film 20 and the p electrode 21.

  The present invention is also applicable to a nitride semiconductor laser element having a current confinement layer having a structure different from that of the nitride semiconductor laser element having a stripe-shaped ridge structure waveguide as described above. The current confinement layer is a layer having a function of selectively flowing a current, and a specific composition is AlN. The current confinement layer may be provided between the Act layer 15 and the p-Contact layer 19, and is preferably formed in the p-Guide layer 17. The interval between the current confinement layers is 0.5 μm to 3 μm. The film thickness of the current confinement layer is 10 nm to 1 μm.

The figure which shows typically an example of the cross-section of the 440 nm band nitride semiconductor laser element concerning the 1st Embodiment of this invention. The figure which shows typically two examples of the cross-sectional structure of the laser mirror of the nitride semiconductor laser element of FIG. FIG. 2 is a characteristic diagram showing several examples of results obtained by measuring IL characteristics by changing the reflectance of the emission side mirror in the nitride semiconductor laser element of FIG. 1. An example of the measurement result of the relationship between the reflectance of the exit side mirror and the kink for the nitride semiconductor laser device of FIG. 1 and the relationship between the reflectivity of the exit side mirror and the kink for the 400 nm band nitride semiconductor laser device are measured. The figure shown in contrast with an example of the result. The figure which shows typically an example of the cross-section of the 440 nm band nitride semiconductor laser element concerning Example 1 of this invention. The figure which shows typically an example of the cross-section of the nitride semiconductor laser element of 440 nm band which concerns on Example 4 of this invention. FIG. 2 is a plan view schematically showing two types of planar arrangement relations when the p-electrode and the waveguide region of the nitride semiconductor laser element of FIG. 1 are viewed from above. The figure which shows a mode that a kink becomes large gradually as the wavelength of a nitride semiconductor laser element becomes long.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... 1st translucent film | membrane, 2 ... 2nd translucent film | membrane, 10 ... Nitride semiconductor substrate (GaN substrate), 11 ... N side contact layer (n-Contact layer), 12 ... Crack barrier layer ( Crack ... Barrier layer), 13 ... n-side cladding (n-Clad layer), 14 ... n-side light guide layer (n-Guide layer), 15 ... active layer (Act layer), 151 ... first barrier layer (1st Barrier layer), 152 ... 1st well layer (1st Well layer), 153 ... Middle barrier layer (Middle Barrier layer), 154 ... 2nd well layer (2nd Well layer), 155 ... Final barrier layer (Last Barrier layer) ), 16 ... p-side electron confinement layer (p-Cap layer), 17 ... p-side light guide layer (p-Guide layer), 18 ... p-side cladding layer (p-Clad layer), 19 ... p-side contact layer ( p-contact layer), 20 ... buried insulating film, 21 ... first electrode (n electrode), 22 ... second electrode (p electrode), 23 ... pad electrode, 24 ... protective insulating film.

Claims (11)

A first conductive type semiconductor layer made of a nitride semiconductor; a stacked semiconductor layer in which an active layer and a second conductive type semiconductor layer are stacked; a first conductive type semiconductor layer sandwiching the active layer and the active layer; A nitride semiconductor laser device comprising a front-side laser mirror and a rear-side laser mirror located on an end surface substantially perpendicular to a waveguide region of a laser beam composed of a two-conductivity type semiconductor layer, the layer _{is in x Al y Ga 1-x} -y N (0.05 ≦ x ≦ 0.25,0 ≦ y ≦ 0.95,0.05 ≦ x + y ≦ 1), the laser mirrors of the front side The nitride semiconductor laser device is characterized by having a reflectance of 60% or less. The front-side laser mirror is formed by laminating a first light-transmitting film and a second light-transmitting film having different refractive indexes with respect to laser light on one end face of the waveguide region. The nitride semiconductor laser device according to Item 1. The first light-transmitting film is a ZrO ₂ film, the second light-transmitting film is a SiO ₂ film, and a pair comprising the first light-transmitting film and the second light-transmitting film. The nitride semiconductor laser device according to claim 2, wherein 1.5 to 2.5 pairs are stacked. 2. The nitride semiconductor laser element according to claim 1, wherein the front-side laser mirror is formed with a single layer film made of a first light-transmitting film on one end face of the waveguide region. The first translucent film is any one of an Al ₂ O ₃ film, an Nb ₂ O ₅ film, an HfO _x film, an MgO film, a Ta ₂ O ₅ film, an SiON film, an AlO _x N _y film, and a GaO _x film. 5. The nitride semiconductor laser device according to claim 4, wherein the nitride semiconductor laser device is a single-layer film comprising one. 6. The nitride semiconductor laser element according to claim 4, wherein a reflectance of the front side laser mirror is 20% or less. A first conductive type semiconductor layer made of a nitride semiconductor; a stacked semiconductor layer in which an active layer and a second conductive type semiconductor layer are stacked; a first conductive type semiconductor layer sandwiching the active layer and the active layer; A nitride semiconductor laser device comprising a front-side laser mirror and a rear-side laser mirror located on an end surface substantially perpendicular to a waveguide region of a laser beam composed of a two-conductivity type semiconductor layer, the layer _{is in x Al y Ga 1-x} -y N (0.05 ≦ x ≦ 0.25,0 ≦ y ≦ 0.95,0.05 ≦ x + y ≦ 1), the laser mirrors of the front side Is a single layer film made of any one of Al ₂ O ₃ film, Nb ₂ O ₅ film, HfO _x film, MgO film, Ta ₂ O ₅ film, SiON film, AlO _x N _y film, and GaO _x film. It is formed on one end face of the waveguide region. Nitride semiconductor laser device. The rear side laser mirror is formed by laminating a first translucent film and a second translucent film having different refractive indexes with respect to laser light on one end face of the waveguide region. The nitride semiconductor laser element according to claim 1, wherein the reflectance is 90% or more. The first light-transmitting film is a ZrO ₂ film, the second light-transmitting film is a SiO ₂ film, and a pair comprising the first light-transmitting film and the second light-transmitting film. 9. The nitride semiconductor laser device according to claim 8, wherein 4.5 to 6.5 pairs are stacked. 10. The nitride semiconductor laser device according to claim 1, wherein the active layer is capable of emitting light in a wavelength region including blue violet to green. 10. The nitride semiconductor laser element according to claim 1, wherein the active layer has an energy band gap of 420 nm or more and 550 nm or less in terms of light wavelength.

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