Nitride semiconductor laser element

Abstract

To provide a nitride semiconductor laser element capable of suppressing changes in optical characteristics.SOLUTION: A nitride semiconductor laser element 10 comprises a stacked structure 100 and a dielectric multilayer film 150. The dielectric multilayer film 150 comprises, in order from a resonator end face side, a first dielectric film 120, a second dielectric film 130, and a third dielectric film 140. The nitride semiconductor laser element 10 satisfies Σnk*dk+ni*di+nj*dj=m1*λ / 4±λ / 16 and nj*dj=m2:λ / 4±λ / 16, when m3 is a positive integer, furthermore it satisfies Σnk*dk+ni*di=m3*λ / 4±λ / 16, and a dielectric film is not provided on the surface opposite the surface where the second dielectric film 130 is located in the third dielectric film 140.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a nitride semiconductor laser device. [Background technology]

[0002] Conventionally, a reflective film has been formed on the end faces (front end face and rear end face) of a semiconductor laser element that emits laser light in order to resonate the laser light inside the semiconductor laser element and to allow the resonated laser light to be appropriately emitted from the semiconductor laser element (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-219436 Summary of the Invention [Problem to be solved by the invention]

[0004] The reflective film formed on the facet of the semiconductor laser element may be deformed by absorbing the laser light from the semiconductor laser element, which changes the optical properties of the reflective film, such as the transmittance and reflectance of the laser light.

[0005] The present disclosure provides a nitride semiconductor laser device capable of suppressing changes in optical characteristics. [Means for solving the problem]

[0006] A nitride semiconductor laser element according to one aspect of the present disclosure includes: a stacked structure made of a plurality of semiconductor layers including a waveguide, the stacked structure having a pair of cavity facets facing each other; and a dielectric multilayer film disposed on at least one of the pair of cavity facets, the dielectric multilayer film having, from the cavity facet side, a first dielectric film, a second dielectric film, and a third dielectric film, in this order, the first dielectric film being made up of n (n is a positive integer) protective films, from a first protective film to an n-th protective film, in that order from the cavity facet side; when the refractive index and film thickness of the k-th (k is an integer satisfying 1≦k≦n) protective film in the first dielectric film are denoted by nk and dk, respectively; the refractive index and film thickness of the second dielectric film are denoted by ni and di, respectively; the refractive index and film thickness of the third dielectric film are denoted by nj and dj, respectively; m1 is an integer equal to or greater than 2; and m2 is a positive integer,

number

number

[0007] According to the present disclosure, it is possible to provide a nitride semiconductor laser element capable of suppressing changes in optical characteristics. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic cross-sectional view showing the configuration of a nitride semiconductor laser device according to an embodiment. [Figure 2] FIG. 2 is a diagram schematically showing an example of deformation of a dielectric film when the nitride semiconductor laser element according to the embodiment emits laser light. [Figure 3]FIG. 3 is a graph showing the reflectance of a dielectric multilayer film versus wavelength in a nitride semiconductor laser device according to a comparative example. [Figure 4] FIG. 4 is a schematic cross-sectional view showing the semiconductor laser device according to the embodiment taken along line IV-IV in FIG. [Figure 5] FIG. 5 is a table showing the change in film thickness with respect to the aging conditions. [Figure 6A] FIG. 6A is a graph showing reflectance versus film thickness before aging of a dielectric multilayer film included in a nitride semiconductor laser element according to an embodiment. [Figure 6B] FIG. 6B is a graph showing reflectance versus film thickness after aging of the dielectric multilayer film included in the nitride semiconductor laser element according to the embodiment. [Figure 6C] FIG. 6C is a graph showing the amount of change in reflectance with respect to film thickness before and after aging of the dielectric multilayer film included in the nitride semiconductor laser element according to the embodiment. [Figure 7] FIG. 7 is a diagram for explaining the relationship between the film thickness of the second dielectric film and the third dielectric film and the reflectance of the dielectric multilayer film. [Figure 8A] FIG. 8A is a graph showing reflectance versus film thickness before aging of a dielectric multilayer film included in a nitride semiconductor laser element according to an embodiment. [Figure 8B] FIG. 8B is a graph showing reflectance versus film thickness before aging of the dielectric multilayer film included in the nitride semiconductor laser element according to the embodiment. [Figure 8C] FIG. 8C is a graph showing reflectance versus film thickness before aging of the dielectric multilayer film included in the nitride semiconductor laser element according to the embodiment. [Figure 8D] FIG. 8D is a graph showing reflectance versus film thickness before aging of a dielectric multilayer film included in a nitride semiconductor laser element according to the embodiment. [Figure 8E] FIG. 8E is a graph showing reflectance versus film thickness before aging of a dielectric multilayer film included in a nitride semiconductor laser element according to the embodiment. [Figure 8F] FIG. 8F is a graph showing reflectance versus film thickness before aging of a dielectric multilayer film included in a nitride semiconductor laser element according to the embodiment. [Figure 9A] FIG. 9A is a graph showing the amount of change in reflectance with respect to film thickness before and after aging of a dielectric multilayer film included in a nitride semiconductor laser element according to an embodiment. [Figure 9B] FIG. 9B is a graph showing the amount of change in reflectance with respect to film thickness before and after aging of the dielectric multilayer film included in the nitride semiconductor laser element according to the embodiment. [Figure 9C] FIG. 9C is a graph showing the amount of change in reflectance with respect to film thickness before and after aging of the dielectric multilayer film included in the nitride semiconductor laser element according to the embodiment. [Figure 9D] FIG. 9D is a graph showing the amount of change in reflectance with respect to film thickness before and after aging of the dielectric multilayer film included in the nitride semiconductor laser element according to the embodiment. [Figure 9E] FIG. 9E is a graph showing the amount of change in reflectance with respect to film thickness before and after aging of the dielectric multilayer film included in the nitride semiconductor laser element according to the embodiment. [Figure 9F] FIG. 9F is a graph showing the amount of change in reflectance with respect to film thickness before and after aging of the dielectric multilayer film included in the nitride semiconductor laser element according to the embodiment. [Figure 10] FIG. 10 is a diagram for explaining the relationship between the film thickness of the dielectric multilayer film and the film thickness variation of the dielectric multilayer film according to the embodiment. [Figure 11A] FIG. 11A is a graph showing the amount of change in reflectance with respect to film thickness before and after aging of a dielectric multilayer film included in a nitride semiconductor laser element according to an embodiment. [Figure 11B] FIG. 11B is a graph showing the amount of change in reflectance with respect to film thickness before and after aging of the dielectric multilayer film included in the nitride semiconductor laser element according to the embodiment. [Figure 11C]FIG. 11C is a graph showing the amount of change in reflectance with respect to film thickness before and after aging of the dielectric multilayer film included in the nitride semiconductor laser element according to the embodiment. [Figure 11D] FIG. 11D is a graph showing the amount of change in reflectance with respect to film thickness before and after aging of the dielectric multilayer film included in the nitride semiconductor laser element according to the embodiment. [Figure 11E] FIG. 11E is a graph showing the amount of change in reflectance with respect to film thickness before and after aging of the dielectric multilayer film included in the nitride semiconductor laser element according to the embodiment. [Figure 11F] FIG. 11F is a graph showing the amount of change in reflectance with respect to film thickness before and after aging of the dielectric multilayer film included in the nitride semiconductor laser element according to the embodiment. [Figure 12] FIG. 12 is a graph showing the reflectance of a dielectric multilayer film versus wavelength in a nitride semiconductor laser device according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that each of the embodiments described below represents a specific example of the present disclosure. Therefore, the numerical values, shapes, materials, components, and the arrangement and connection of the components shown in the following embodiments are merely examples and are not intended to limit the present disclosure.

[0010] Furthermore, each figure is a schematic diagram and is not necessarily an exact representation. Therefore, the scales and the like do not necessarily match in each figure. In each figure, the same reference numerals are used to denote substantially the same components, and redundant explanations will be omitted or simplified.

[0011] In this specification, the terms "above" and "below" do not refer to the upward direction (vertically upward) and downward direction (vertically downward) in absolute spatial recognition, but are used as terms defined by a relative positional relationship based on the stacking order in a stacked configuration. Furthermore, the terms "above" and "below" are applied not only to cases where two components are arranged with a gap between them and another component exists between the two components, but also to cases where two components are arranged in contact with each other.

[0012] In this specification and drawings, the X-axis, Y-axis, and Z-axis represent the three axes of a three-dimensional Cartesian coordinate system. In each embodiment, the Z-axis direction is defined as the vertical direction, and the direction perpendicular to the Z-axis (the direction parallel to the XY plane) is defined as the horizontal direction. The positive direction of the Z-axis is defined as the vertically upward direction.

[0013] (Embodiment) [overview] Fig. 1 is a schematic cross-sectional view showing the configuration of a nitride semiconductor laser device 10 according to an embodiment. Fig. 2 is a cross-sectional view showing a schematic example of deformation of a dielectric film when nitride semiconductor laser device 10 according to the embodiment emits laser light 201. Figs. 1 and 2 are cross-sectional views taken along line II in Fig. 4, which will be described later.

[0014] The nitride semiconductor laser device 10 includes a stacked structure 100 having a first conductivity type semiconductor layer 100a, a second conductivity type semiconductor layer 100b, and an active layer 103 sandwiched between the first conductivity type semiconductor layer 100a and the second conductivity type semiconductor layer 100b and emitting laser light 201. A dielectric multilayer film 150 is formed on a front end facet 100F of the nitride semiconductor laser device 10 to resonate the laser light 201 within the stacked structure 100 and effectively emit the laser light 201 from the front end facet 100F. The dielectric multilayer film 150 includes, for example, a first dielectric film 120, a second dielectric film 130, and a third dielectric film 140. Specifically, the first dielectric film 120, the second dielectric film 130, and the third dielectric film 140 are arranged in this order on the front end facet 100F of the stacked structure 100.

[0015] The first dielectric film 120 is a film that protects the front end face 100F and suppresses oxidation of the front end face 100F due to the diffusion of oxygen from the outside. The second dielectric film 130 and the third dielectric film 140 are each a film for adjusting the reflectance.

[0016] The first dielectric film 120, the second dielectric film 130, and the third dielectric film 140 are formed with a substantially uniform thickness on the front end face 100F.

[0017] Conventionally, when designing the reflectance of the dielectric multilayer film 150, it was not necessary to take into consideration the film thickness distribution of the dielectric multilayer film 150, and the film thickness and material of the dielectric multilayer film 150 were designed so that the reflectance was maximum or minimum relative to the oscillation wavelength of the laser light 201 emitted from the stacked structure 100.

[0018] In recent years, there has been a blue-violet high-power laser element with an oscillation wavelength of about 405 nm and an optical output of the laser beam 201 of 1 W or more. The inventors of the present application have found that when such a blue-violet high-power laser element is aged for a long time (i.e., the laser beam 201 is continuously emitted), the film of the dielectric multilayer film 150 in the vicinity of the portion (light-emitting point) from which the laser beam 201 is emitted on the front end face 100F is altered.

[0019] For example, as shown in FIG. 2, the second dielectric film 130 and the third dielectric film 140 may be deformed by absorbing the laser light 201 emitted from the stacked structure 100.

[0020] For example, by emitting laser light 201 from the stacked structure 100, the film thicknesses of the second dielectric film 130 and the third dielectric film 140 differ between film thickness 300 in the portion through which the laser light 201 passes and film thickness 301 in the portion through which the laser light 201 does not pass. In other words, the film thicknesses 300, 301 of the second dielectric film 130 and the third dielectric film 140 change by emitting laser light 201 from the stacked structure 100.

[0021] 3 is a graph showing the reflectance of the dielectric multilayer film versus wavelength for a nitride semiconductor laser device according to a comparative example. The nitride semiconductor laser device according to the comparative example is similar to nitride semiconductor laser device 10 according to the embodiment except for the material, film thickness, and refractive index used for the dielectric multilayer film. The reflectance before aging shown in FIG. 3 is the reflectance of light in a state that is not deformed by laser light 201, such as dielectric multilayer film 150 shown in FIG. 1. On the other hand, the reflectance after aging shown in FIG. 3 is the reflectance of light in a state that is deformed by laser light 201, such as dielectric multilayer film 150 shown in FIG. 2.

[0022] As shown in Fig. 3, the reflectance before aging and the reflectance after aging have different peak positions located near a wavelength of 400 nm. Specifically, the reflectance of the dielectric multilayer film according to the comparative example increases by about 1.5% at the peak reflectance located near a wavelength of 400 nm by absorbing laser light. Therefore, the optical characteristics (specifically, optical output) of the nitride semiconductor laser element according to the comparative example differ before and after aging. Therefore, for example, if nitride semiconductor laser element 10 is used continuously, the optical characteristics change over time.

[0023] As a result of extensive research, the present inventors have found that changes in optical characteristics can be suppressed by appropriately setting the material, film thickness, refractive index, etc. of the dielectric multilayer film 150 included in the nitride semiconductor laser device 10. Specifically, the present inventors have found that there are films whose film thickness increases and decreases during aging. Therefore, the present inventors have found that by appropriately combining films whose film thickness increases and decreases during aging, it is possible to suppress changes in reflectance even if the film thickness changes during aging.

[0024] The configuration and optical characteristics of the nitride semiconductor laser device 10 according to the embodiment will be specifically described below.

[0025] In the following description, emitting the laser light 201 from the laminated structure 100 is also simply referred to as aging.

[0026] [composition] The configuration of the nitride semiconductor laser device 10 will be described with reference to FIGS.

[0027] FIG. 4 is a cross-sectional view showing the nitride semiconductor laser device 10 according to the embodiment taken along line IV-IV in FIG.

[0028] The nitride semiconductor laser device 10 is a nitride semiconductor light emitting device that emits laser light 201 .

[0029] The nitride semiconductor laser device 10 includes a layered structure 100 and a dielectric multilayer film 150 .

[0030] The laminated structure 100 is a laminate made up of multiple semiconductor layers including a waveguide 110. The laminated structure 100 also has a pair of opposing cavity end faces, a front end face 100F and a rear end face 100R. The dielectric multilayer film 150 is disposed on at least one of the pair of cavity end faces. In this embodiment, the dielectric multilayer film 150 is disposed on the front end face 100F.

[0031] The stacked structure 100 includes a substrate 101, a first semiconductor layer 102, an active layer 103, a second semiconductor layer 104, a contact layer 105, an insulating layer 106, a second electrode 107, a pad electrode 108, and a first electrode 109. The first conductivity type semiconductor layer 100a in FIG. 1 includes the substrate 101 and the first semiconductor layer 102, and the second conductivity type semiconductor layer 100b includes the second semiconductor layer 104 and the contact layer 105. Note that the insulating layer 106, the second electrode 107, the pad electrode 108, and the first electrode 109 are not shown in FIG. 1. In this embodiment, the stacked structure 100 is formed of a gallium nitride-based material, which is an example of a nitride material. As a result, for example, by setting the input current to stacked structure 100 to 2 A or more and 10 A or less and the input voltage to 4 V or more and 6 V or less, it is possible to realize nitride semiconductor laser device 10 having optical characteristics of emitting laser light 201 having a wavelength in a band of approximately 390 nm or more and 420 nm or less and an optical output of approximately 3 W or more and 10 W or less. As such, in this embodiment, nitride semiconductor laser device 10 emits laser light 201 of 1 W or more. Furthermore, the oscillation wavelength of nitride semiconductor laser device 10 is 420 nm or less. More specifically, stacked structure 100 emits laser light 201 having a peak wavelength of 400 nm.

[0032] Furthermore, for example, the optical density of the laser light 201 is 0.1 W / μm or more. The optical density is the optical output of the laser light 201 divided by the stripe width. The stripe width here is, for example, the horizontal width of a ridge portion (length in the X-axis direction in this embodiment) which will be described later. The width of the ridge portion (hereinafter also referred to as stripe width) is, for example, approximately 30 μm or more and 100 μm or less.

[0033] The resonator length of the multilayer structure 100 (in this embodiment, the length in the Y-axis direction) is, for example, not less than 1200 μm and not more than 5000 μm.

[0034] The optical characteristics of the nitride semiconductor laser device 10 are not limited to those described above. For example, the nitride semiconductor laser device 10 may have optical characteristics of emitting laser light 201 having a wavelength in a band of approximately 365 nm to 390 nm and an optical output of approximately 1 W to 5 W by applying a current of 2 A to 10 A and an applied voltage of 3.5 V to the stacked structure 100. In this case, the stripe width is, for example, approximately 8 μm to 100 μm. Furthermore, in this case, the cavity length of the stacked structure 100 is, for example, approximately 800 μm to 5000 μm.

[0035] Substrate 101 is a plate-like member that serves as the base material of stacked structure 100. In this embodiment, substrate 101 is a GaN single crystal substrate with a thickness of 100 μm. The thickness of substrate 101 is not limited to 100 μm and may be, for example, 50 μm or more and 120 μm or less. Furthermore, the material forming substrate 101 is not limited to GaN single crystal and may be sapphire, SiC, or the like.

[0036] The first semiconductor layer 102 is a semiconductor layer of a first conductivity type disposed above the substrate 101. In this embodiment, the first semiconductor layer 102 is an n-type semiconductor layer disposed on one main surface of the substrate 101, and includes an n-type cladding layer. The n-type cladding layer is a layer made of n-AlGaN. Note that the configuration of the n-type cladding layer is not limited to this.

[0037] The active layer 103 is a light-emitting layer disposed above the first semiconductor layer 102. In this embodiment, the active layer 103 is a quantum well active layer in which well layers made of InGaN and barrier layers made of GaN are alternately stacked, and has two well layers. By providing such an active layer 103, the nitride semiconductor laser device 10 can emit blue laser light with a wavelength of approximately 400 nm. The configuration of the active layer 103 is not limited to this, and it may be a quantum well active layer in which well layers and barrier layers are alternately stacked. The active layer 103 may include a guide layer formed at least either above or below the quantum well active layer.

[0038] The second semiconductor layer 104 is a semiconductor layer of a second conductivity type disposed above the active layer 103. The second conductivity type is a conductivity type different from the first conductivity type. In this embodiment, the second semiconductor layer 104 is a p-type semiconductor layer and includes a p-type cladding layer. The p-type cladding layer is a superlattice layer in which 100 layers of p-AlGaN and 3-nm-thick layers of GaN are alternately stacked. Note that the configuration of the p-type cladding layer is not limited to this.

[0039] The first semiconductor layer 102, the active layer 103, and the second semiconductor layer 104 form a waveguide 110 which is a waveguide portion for the laser light 201.

[0040] The waveguide 110 is a portion where the laser light 201 is guided inside the laminated structure 100. The waveguide 110 is made up of, for example, a part of the first semiconductor layer 102, a part of the active layer 103, and a part of the second semiconductor layer 104.

[0041] The contact layer 105 is a semiconductor layer of a second conductivity type that is in ohmic contact with the second electrode 107. In this embodiment, the contact layer 105 is a p-type semiconductor layer made of p-GaN. However, the configuration of the contact layer 105 is not limited to this.

[0042] In this embodiment, a ridge portion is formed in the second semiconductor layer 104 and the contact layer 105. A region of the active layer 103 corresponding to the ridge portion (i.e., a region of the active layer 103 located below the ridge portion) serves as a light emitting point, and emits laser light 201.

[0043] The first electrode 109 is an electrode disposed on the lower main surface of the substrate 101 (i.e., the main surface on which the first semiconductor layer 102 and the like are not disposed). The first electrode 109 is, for example, a laminated film in which Ti, Pt, and Au are laminated in this order from the substrate 101 side. The configuration of the first electrode 109 is not limited to this.

[0044] The second electrode 107 is an electrode disposed on the contact layer 105. In this embodiment, the second electrode 107 is a p-side electrode that is in ohmic contact with the contact layer 105. A pad electrode 108 is disposed on the p-side electrode.

[0045] The second electrode 107 is, for example, a laminated film in which Pd and Pt are laminated in this order from the contact layer 105 side. The configuration of the second electrode 107 is not limited to this.

[0046] The pad electrode 108 is a pad-shaped electrode disposed above the second electrode 107. The pad electrode 108 is, for example, a laminated film in which Ti and Au are laminated in this order from the second electrode 107 side, and is disposed on the ridge portion and its periphery. Note that the configuration of the pad electrode 108 is not limited to this.

[0047] Although not shown in FIG. 4, the laminated structure 100 may further include an insulating film such as an SiO 2 film that covers the sidewalls of the ridge portion, in addition to the above layers.

[0048] In this embodiment, the stacked structure 100 is a so-called single emitter having one ridge portion (emitter), but may be a so-called multi-emitter having a plurality of ridge portions (for example, about 60). In this case, for example, the total optical output of the laser light 201 emitted from below each of the plurality of ridge portions in the stacked structure 100 is about 100 W or more and 200 W or less.

[0049] The dielectric multilayer film 150 is a protective film disposed on the front end face 100F of the laminated structure 100. Specifically, the dielectric multilayer film 150 protects the front end face 100F of the laminated structure 100 and reduces the reflectance of the laser light 201 at the front end face 100F. The dielectric multilayer film 150 has, in this order from the cavity end face (front end face 100F in this embodiment) side, a first dielectric film 120, a second dielectric film 130, and a third dielectric film 140.

[0050] The first dielectric film 120 is the dielectric layer among the first dielectric film 120, the second dielectric film 130, and the third dielectric film 140 that is arranged closest to the front end facet 100F. The first dielectric film 120 may include at least one dielectric film made of at least one of a nitride film and an oxynitride film. This reduces oxygen diffusion from the outside of the dielectric multilayer film 150 to the stacked structure 100. This makes it possible to suppress deterioration of the front end facet 100F of the stacked structure 100. This enables the nitride semiconductor laser device 10 to operate for a long period of time.

[0051] Furthermore, the first dielectric film 120 is directly connected to the front end face 100F of the stacked structure 100. That is, the first dielectric film 120 is formed in contact with the front end face 100F. Therefore, by using a nitride film or an oxynitride film having the same crystallinity as the stacked structure 100 as the first dielectric film 120, the protection performance of the front end face 100F can be improved.

[0052] For example, the first dielectric film 120 is made up of n (n is a positive integer) layers of protective films, from a first protective film to an n-th protective film, in that order from the front end face 100F side. In this embodiment, n=4, and the first dielectric film 120 has a first protective film 121, a second protective film 122, a third protective film 123, and a fourth protective film 124.

[0053] The first protective film 121 is a dielectric film that is arranged closest to the front end facet 100F among the multiple protective films that the first dielectric film 120 has. In this embodiment, the first protective film 121 is a film that includes a SiN film. More specifically, the first protective film 121 is a film made of a SiN film with a thickness d1 of about 0.5 nm. The configuration of the first protective film 121 is not limited to this. The first protective film 121 may be, for example, another oxynitride film such as SiON.

[0054] The second protective film 122 is a dielectric film laminated on the first protective film 121. In this embodiment, the second protective film 122 is a film including an AlON film. More specifically, the second protective film 122 is a film made of an AlON film having a thickness d2 of approximately 21 nm. The configuration of the second protective film 122 is not limited to this. The second protective film 122 may be, for example, another oxynitride film such as SiON, or a nitride film such as an AlN film or a SiN film.

[0055] The third protective film 123 is a dielectric film laminated on the second protective film 122. In this embodiment, the third protective film 123 is an Al2O3 film having a thickness d3 of approximately 13 nm. However, the configuration of the third protective film 123 is not limited to this. The third protective film 123 may be another dielectric film such as SiO2.

[0056] The fourth protective film 124 is a dielectric film laminated on the third protective film 123. The fourth protective film 124 may include a dielectric film made of at least one of a nitride film and an oxynitride film. In this embodiment, the fourth protective film 124 is a film made of an AlON film having a thickness d4 of approximately 11 nm. The configuration of the fourth protective film 124 is not limited to this. The fourth protective film 124 may be, for example, another nitride film such as SiN, or an oxynitride film such as an AlN film or a SiON film.

[0057] The second dielectric film 130 is a dielectric film laminated on the outside of the first dielectric film 120. In this embodiment, the second dielectric film 130 is an Al2O3 film with a thickness di of about 167 nm.

[0058] The third dielectric film 140 is a dielectric film laminated on the outside of the second dielectric film 130. In this embodiment, the third dielectric film 140 is an SiO2 film with a thickness dj of about 58 nm.

[0059] 5 is a table showing the change in film thickness with respect to the aging conditions. Note that under both Condition 1 and Condition 2, the peak wavelength (oscillation wavelength) of the laser light 201 is 405 nm.

[0060] 5, when 4.5 W laser light 201 was emitted from the stacked structure 100 at 25° C. for 736 hours, the rate of change in the film thickness of the second dielectric film 130 made of an Al2O3 film was −8.5% at maximum and −6.2% at minimum due to variations in the light intensity distribution of the laser light 201. Furthermore, under condition 1, the rate of change in the film thickness of the third dielectric film 140 made of an SiO2 film was +5.3% at maximum and 3.7% at minimum.

[0061] The optical density under condition 1 is 0.15 (W / μm).

[0062] 5, when 1 W laser light 201 was emitted from the stacked structure 100 for 4500 hours at 25°C, the rate of change in the thickness of the second dielectric film 130 made of an Al2O3 film was -8.7% at maximum and -7.0% at minimum. Also, under condition 2, the rate of change in the thickness of the third dielectric film 140 made of an SiO2 film was +5.2% at maximum and 4.0% at minimum.

[0063] The optical density under condition 2 is 0.149 (W / μm).

[0064] The rate of change in thickness of the second dielectric film 130 made of an Al2O3 film under conditions 1 and 2 was -7.6% on average. The rate of change in thickness of the third dielectric film 140 made of an SiO2 film under conditions 1 and 2 was +4.6% on average.

[0065] Furthermore, when the optical density was about 0.15 W / μm, the rate of change in the film thickness of the second dielectric film 130 made of Al2O3 film decreased sharply within 1000 hours of aging, and then gradually decreased, although the change became more gradual, after 1000 hours of aging. Furthermore, when the optical density was about 0.15 W / μm, the rate of change in the film thickness of the third dielectric film 140 made of SiO2 film increased sharply within 1000 hours of aging, and then gradually increased, although the change became more gradual, after 1000 hours of aging.

[0066] As described above, the second dielectric film 130 made of Al2O3 shrinks and its thickness decreases due to aging. A film made of Al2O3 is amorphous immediately after deposition (as-depo.) containing a few percent of Ar. However, it is thought that the as-depo. Al2O3 film shrinks and its thickness decreases as Ar is desorbed due to the optical load caused by aging.

[0067] On the other hand, the third dielectric film 140 made of SiO2 expands due to aging and increases in thickness. It is believed that the third dielectric film 140 made of SiO2 expands and increases in thickness as a result of Ar being desorbed from the second dielectric film 130 made of Al2O3 and diffusing into the SiO2 film.

[0068] For this reason, materials whose film expands with aging are considered to be materials whose amorphous state is stable and materials whose molecular bonds have a degree of freedom and which tend to contain impurity atoms. Examples of such materials include SiO2, B2O3, P2O5, and GeO2. In this embodiment, the third dielectric film 140 has an amorphous structure. Also, for example, the third dielectric film 140 is any one of SiO2, B2O3, P2O5, and GeO2.

[0069] Furthermore, materials that shrink due to aging include materials that are more stable in a crystalline state than in an amorphous state, and materials with strong interatomic bonds that are less likely to contain impurity atoms. Examples of such materials include Al2O3, Ta2O5, and ZrO2. For example, the second dielectric film 130 is any of Al2O3, Ta2O5, and ZrO2.

[0070] As described above, one of the second dielectric film 130 and the third dielectric film 140 has a property of being decreased in thickness by the laser beam 201 emitted from the nitride semiconductor laser element 10. The other has a property of being increased in thickness by the laser beam 201 emitted from the nitride semiconductor laser element 10. In the present embodiment, the second dielectric film 130 has a property of being decreased in thickness by the laser beam 201 emitted from the nitride semiconductor laser element 10. The third dielectric film 140 has a property of being increased in thickness by the laser beam 201 emitted from the nitride semiconductor laser element 10. Specifically, upon receiving the laser beam 201 emitted from the front-side end facet 100F, at the interface between the second dielectric film 130 and the third dielectric film 140, a recess 131 is formed in the second dielectric film 130 and a protrusion 141 is formed in the third dielectric film 140. Furthermore, for example, the change in the film thickness of the second dielectric film 130 and the third dielectric film 140 occurs on the optical path (for example, on the optical axis 200 of the laser light 201) of the laser light 201 emitted from the front end facet 100F.

[0071] According to the nitride semiconductor laser element 10 having the dielectric multilayer film 150 made of such a material, since the dielectric multilayer film 150 has a film thickness and a refractive index as described below, even if the laser light 201 is emitted for about 10,000 hours, the reduction rate of the optical output is 20% or less.

[0072] A coating film 160 may be disposed between the front end facet 100F and the dielectric multilayer film 150.

[0073] Coating film 160 is a film that protects front end face 100F and is, for example, an aluminum oxynitride film. The aluminum oxynitride film may contain crystalline aluminum nitride. Specifically, the aluminum oxynitride film may be crystalline aluminum nitride.

[0074] The material used for the coating film 160 is not limited to this. For example, the material used for the coating film 160 may be at least one of aluminum silicon nitride, aluminum gallium nitride, aluminum yttrium nitride, aluminum lanthanum nitride, aluminum silicon oxynitride, aluminum gallium oxynitride, aluminum yttrium oxynitride, and aluminum lanthanum oxynitride. The first dielectric film 120 may be made of the above-mentioned materials.

[0075] Furthermore, such a dielectric multilayer film 150 has a film thickness and refractive index as described below, so that the reflectance for light with a wavelength of 400 nm is, for example, about 4% or more and 20% or less. Furthermore, by employing a so-called AR (Anti Reflection) coating technique for the dielectric multilayer film 150, the reflectance of the dielectric multilayer film 150 for light with a wavelength of 400 nm may be set to 0.1% or less.

[0076] The dielectric multilayer film 150 may also be provided on the rear end face 100R.

[0077] [Optical properties] Next, the optical characteristics of the nitride semiconductor laser device 10 according to the embodiment will be described.

[0078] The inventors of the present application performed optical simulations to determine the conditions under which the reflectance changes little even when the film thickness changes in the dielectric multilayer film 150. In the following optical simulations, the second dielectric film 130 is an Al2O3 film, and the third dielectric film 140 is an SiO2 film.

[0079] Fig. 6A is a graph showing reflectance versus film thickness before aging of dielectric multilayer film 150 included in nitride semiconductor laser device 10 according to the embodiment. Fig. 6B is a graph showing reflectance versus film thickness after aging of dielectric multilayer film 150 included in nitride semiconductor laser device 10 according to the embodiment. Fig. 6C is a graph showing the amount of change in reflectance versus film thickness before and after aging of dielectric multilayer film 150 included in nitride semiconductor laser device 10 according to the embodiment.

[0080] 6A to 6C, the film thickness, refractive index, and other conditions of the first dielectric film 120 are fixed. Also, in Figures 6A to 6C, the second dielectric film 130 is an Al2O3 film, and the third dielectric film 140 is an SiO2 film. In Figures 6A to 6C, the film thicknesses of these films are changed in the range of 0 nm to 300 nm, and the reflectance is calculated and displayed as a contour line.

[0081] 6B shows the film thickness before aging. Specifically, the graph shown in Fig. 6B shows the calculated reflectance in contour lines when the film thickness of the second dielectric film 130 is increased by -7.6% and the film thickness of the third dielectric film 140 is increased by +4.6% compared to the film thicknesses of the second dielectric film 130 and the third dielectric film 140 before aging.

[0082] Fig. 6C shows the calculation results of the difference in reflectance before and after aging. Specifically, the graph shown in Fig. 6C shows the value obtained by subtracting the reflectance shown in Fig. 6B from the reflectance shown in Fig. 6A.

[0083] In addition, in FIG. 6C, contour lines are shown in increments of +3% for the amount of change in reflectance on the positive side, starting from +1.5%, and contour lines are shown in increments of -3% for the amount of change in reflectance on the negative side, starting from -1.5%.

[0084] It can be seen from FIG. 6C that there is a region where the change in reflectance before and after aging is between −1.5% and +1.5%.

[0085] 7 is a diagram illustrating the relationship between the film thickness of the second dielectric film 130 and the third dielectric film 140 and the reflectance of the dielectric multilayer film 150. The graph showing the reflectance versus film thickness shown in FIG. 7 is the same as FIG. 6A.

[0086] If the one or more protective films (four protective films in this embodiment) in the first dielectric film 120 are n layers of films, namely, the first protective film, the second protective film, ..., and the nth protective film, in that order from the front end face 100F side, and the refractive index and film thickness of the kth (k is a positive integer) protective film are nk and dk, respectively, the refractive index and film thickness of the second dielectric film 130 are ni and di, respectively, the refractive index and film thickness of the third dielectric film 140 are nj and dj, respectively, and the sum of the optical film thicknesses of the one or more protective films in the first dielectric film 120 is A, then the following formula (1) is satisfied.

[0087]

number

[0088] Moreover, dashed lines 400 to 407 shown in FIG. 7 satisfy the following formula (2) in order from the left side of the page.

[0089] A=m1×λ / 4 Formula (2)

[0090] Here, m1 is a positive integer. For example, dashed line 400 is a straight line obtained when m1 = 1 is substituted into equation (2). Similarly, dashed line 401 is a straight line obtained when m1 = 2 is substituted into equation (2). Similarly, dashed line 402 is a straight line obtained when m1 = 3 is substituted into equation (2). Similarly, dashed line 403 is a straight line obtained when m1 = 4 is substituted into equation (2). Similarly, dashed line 404 is a straight line obtained when m1 = 5 is substituted into equation (2). Similarly, dashed line 405 is a straight line obtained when m1 = 6 is substituted into equation (2). Similarly, dashed line 406 is a straight line obtained when m1 = 7 is substituted into equation (2). Similarly, dashed line 407 is a straight line obtained when m1 = 8 is substituted into equation (2).

[0091] Here, the reflectance of the dielectric multilayer film 150 takes a maximum value when m1 is an even number, and takes a minimum value when m1 is an odd number.

[0092] Furthermore, the change in the reflectance between maximum and minimum in the dielectric multilayer film 150 coincides with the period of cos(4π×nj×dj / λ), which is the proportional term of film thickness in the relational expression between the optical film thickness and reflectance of the SiO2 film, which is the third dielectric film 140, derived from Fresnel's equation. That is, the product of the film thickness and refractive index of the third dielectric film 140 (i.e., optical film thickness) at which the reflectance of the dielectric multilayer film 150 becomes maximum or minimum satisfies the following formula (3):

[0093] B=nj×dj=N1×λ / 4 Equation (3)

[0094] The optical refractive index and film thickness of the third dielectric film 140 are nj and dj, respectively. N1 is 0 or a positive integer. For example, when N1=1, B is represented by dashed line 410. For example, when N1=2, B is represented by dashed line 411. For example, when N1=3, B is represented by dashed line 412. For example, when N1=4, B is represented by dashed line 413.

[0095] The above formula (3) is satisfied even if the film thickness of the first dielectric film 120 is changed.

[0096] On the other hand, although the relationship between the optical thickness and reflectance of the second dielectric film 130 has a period of λ / 4 between the maximum and minimum, the optical thickness at which the maximum or minimum occurs is affected by the thickness of the first dielectric film 120, and therefore is not necessarily an integer multiple of λ / 4.

[0097] Here, when the sum of the optical film thicknesses of the first dielectric film 120 and the second dielectric film 130 is D, the following formula (4) is satisfied.

[0098]

number

[0099] Furthermore, the film thickness and refractive index of the second dielectric film 130 at which the reflectance of the dielectric multilayer film 150 becomes the maximum or minimum satisfy the following formula (5).

[0100] D=N2×λ / 4 Equation (5)

[0101] The refractive index and film thickness of the second dielectric film 130 are ni and di, respectively. N2 is a positive integer. For example, when N2=1, D is represented by dashed line 420. For example, when N2=2, B is represented by dashed line 421. For example, when N2=3, B is represented by dashed line 422. For example, when N2=4, B is represented by dashed line 423. For example, when N2=5, B is represented by dashed line 424.

[0102] The above formula (5) is satisfied even if the ratio between the film thickness of the first dielectric film 120 and the film thickness of the second dielectric film 130 is changed.

[0103] Next, a change in film thickness when the film thickness of the first dielectric film 120 is changed will be described.

[0104] 8A to 8F are graphs showing reflectance versus film thickness before and after aging of dielectric multilayer film 150 included in nitride semiconductor laser device 10 according to the embodiment. Figures 9A to 9F are graphs showing the amount of change in reflectance versus film thickness before and after aging of dielectric multilayer film 150 included in nitride semiconductor laser device 10 according to the embodiment.

[0105] 8A and 9A are graphs when the optical thickness of the first dielectric film 120 is λ / 8. FIGS. 8B and 9B are graphs when the optical thickness of the first dielectric film 120 is 3×λ / 16. FIGS. 8C and 9C are graphs when the optical thickness of the first dielectric film 120 is λ / 4. FIGS. 8D and 9D are graphs when the optical thickness of the first dielectric film 120 is 5×λ / 16. FIGS. 8E and 9E are graphs when the optical thickness of the first dielectric film 120 is 3×λ / 8. FIGS. 8F and 9F are graphs when the optical thickness of the first dielectric film 120 is λ / 2.

[0106] Here, λ represents the oscillation wavelength of the laser light 201, which is 400 nm in this embodiment.

[0107] 9A to 9F, the amount of change in reflectance on the positive side is shown as contour lines in increments of +3% starting from +1.5%, and the amount of change in reflectance on the negative side is shown as contour lines in increments of -3% starting from -1.5%.

[0108] 9B, 9C, and 9D, it can be seen that the change in reflectance is approximately −1.5% or more and +1.5% or less within dashed line 430. Dashed line 430 indicates the range in which the film thickness of second dielectric film 130 is 3×λ / 4 or less and the film thickness of third dielectric film 140 is 3×λ / 4 or less.

[0109] From the above, by setting the first film thickness condition such that the optical film thickness of the first dielectric film 120 (more specifically, the sum of the optical film thicknesses of the multiple protective films that the first dielectric film 120 has) is 3×λ / 16 or more and 5×λ / 16 or less, the optical film thickness of the second dielectric film 130 is 3×λ / 4 or less, and the optical film thickness of the third dielectric film 140 is 3×λ / 4 or less, it is possible to reduce the amount of change in reflectance of the dielectric multilayer film 150 to approximately −1.5% or more and +1.5% or less even when aged. In other words, the first dielectric film 120 satisfies the following formula (6).

[0110]

number

[0111] Next, the relationship between the film thickness of the dielectric multilayer film 150 and the film thickness variation of the dielectric multilayer film 150 will be described.

[0112] When a plurality of nitride semiconductor laser elements 10 are manufactured in which a dielectric multilayer film 150 is formed on a stacked structure 100, even if an attempt is made to manufacture the dielectric multilayer film 150 with the same film thickness, the film thickness of each of the dielectric multilayer films 150 of the plurality of nitride semiconductor laser elements 10 will not be completely consistent due to manufacturing variations.

[0113] Fig. 10 is a diagram for explaining the relationship between the film thickness of the dielectric multilayer film 150 and the film thickness variation of the dielectric multilayer film 150. The graph showing the reflectance versus film thickness shown in Fig. 10 is the same as Fig. 6A.

[0114] At the maximum value, minimum value, and saddle point of the reflectance in the graph shown in Fig. 10, the change in reflectance relative to the change in film thickness of the dielectric multilayer film 150 is small, that is, it is considered to be stable. The maximum value, minimum value, and saddle point of the reflectance in the graph shown in Fig. 10 are intersections 440 to 443 between any of the dashed lines 400 to 404 and any of the dashed lines 410 to 413 shown in Fig. 10. In other words, the maximum value, minimum value, and saddle point of the reflectance in the graph shown in Fig. 10 are film thicknesses that satisfy the above-mentioned formula (1) and formula (3).

[0115] For example, when A in the above formula (1) is an even number and B in the above formula (3) is an even number, the reflectance exhibits a maximum and becomes one of multiple intersections 440. Furthermore, when A in the above formula (1) is an even number and B in the above formula (3) is an odd number, the reflectance exhibits a saddle point and becomes one of multiple intersections 441. For example, when A in the above formula (1) is an odd number and B in the above formula (3) is an even number, the reflectance exhibits a saddle point and becomes one of multiple intersections 442. For example, when A in the above formula (1) is an odd number and B in the above formula (3) is an even number, the reflectance exhibits a minimum and becomes one of multiple intersections 443.

[0116] Here, in order to realize a high reflectance of the dielectric multilayer film 150, it is better to select the intersection 440 or 443, and in order to realize a low reflectance, it is better to select the intersection 441 or 442.

[0117] As described above, in the vicinity of the intersections 440 to 443, it is possible to reduce the change in reflectance relative to the change in film thickness of the dielectric multilayer film 150. For example, in the range of the region surrounded by the dashed line 450 of the parallelogram indicating the vicinity of the intersections 440 to 443, it is possible to reduce the change in reflectance relative to the change in film thickness of the dielectric multilayer film 150. Such a region surrounded by the dashed line 450 satisfies the following formulas (7) and (8).

[0118]

number

[0119] B1=nj×dj=m2×λ / 4±λ / 16 Equation (8)

[0120] Note that m1 and m2 are both positive integers.

[0121] By setting such a second film thickness condition, it is possible to reduce the change in reflectance with respect to the change in film thickness of the dielectric multilayer film 150. Furthermore, by setting m1 to an integer of 2 or greater, it is possible to further reduce the change in reflectance with respect to the change in film thickness of the dielectric multilayer film 150. Furthermore, for example, when m2=1, in other words, by setting the following equation (9), it is possible to further reduce the change in reflectance with respect to the change in film thickness of the dielectric multilayer film 150.

[0122] 3λ / 16≦nj×dj≦5λ / 16 Equation (9)

[0123] Furthermore, the following formula (10) is calculated from the relationship between the above formula (4), the above formula (5), and the area surrounded by the dashed line 450 of the parallelogram showing the vicinity of the intersections 440 to 443.

[0124]

number

[0125] Note that m3 is a positive integer.

[0126] This makes it possible to suppress fluctuations (changes) in the reflectance of the dielectric multilayer film 150 even when the nitride semiconductor laser device 10 is driven (when the nitride semiconductor laser device 10 is made to emit laser light 201).As a result, it is possible to suppress fluctuations in the optical output of the nitride semiconductor laser device 10 while it is being driven, and to suppress deterioration of the nitride semiconductor laser device 10.

[0127] From the above, by satisfying the above-mentioned first film thickness condition and the above-mentioned second film thickness condition, it is possible to reduce the amount of change in reflectance of the dielectric multilayer film 150 even when aging occurs, and to reduce the change in reflectance relative to the change in film thickness of the dielectric multilayer film 150. In other words, according to the nitride semiconductor laser device 10 including the dielectric multilayer film 150 that satisfies the above-mentioned first film thickness condition and the above-mentioned second film thickness condition, it is possible to suppress changes in optical characteristics.

[0128] 11A to 11F are graphs showing the amount of change in reflectance versus film thickness before and after aging of dielectric multilayer film 150 included in nitride semiconductor laser device 10 according to the embodiment. The graphs showing reflectance versus film thickness shown in FIGS. 11A to 11F are the same as those in FIGS. 9A to 9F.

[0129] Within the range of the area surrounded by the dashed line 450 shown in FIGS. 11A to 11F, the change in reflectance relative to the change in the film thickness of the dielectric multilayer film 150 can be made small.

[0130] 11B to 11D, the amount of change in reflectance of the dielectric multilayer film 150 can be reduced even when aging occurs, so long as the reflectance is within the range surrounded by the rectangular dashed line 430. In other words, the change in the optical properties of the dielectric multilayer film 150 can be further suppressed so long as the reflectance is within the range surrounded by the dashed line 430 and the range surrounded by the dashed line 450 shown in FIGS.

[0131] Fig. 12 is a graph showing the reflectance of the dielectric multilayer film 150 versus the wavelength of the nitride semiconductor laser device 10 according to the embodiment. The graph shown in Fig. 12 shows the reflectance of the dielectric multilayer film 150 that satisfies the film thickness condition of the dielectric multilayer film 150 at position 461 shown in Fig. 11C, i.e., the film thickness condition that is within the range of the region surrounded by dashed line 430 and the range of the region surrounded by dashed line 450. The graph shown in Fig. 3 shows the reflectance of the dielectric multilayer film that satisfies the film thickness condition of the dielectric multilayer film 150 at position 460 shown in Fig. 11B, i.e., the film thickness condition that is outside the range of the region surrounded by dashed line 430 and the range of the region surrounded by dashed line 450.

[0132] As shown in FIG. 12, the reflectance of the dielectric multilayer film 150 that satisfies the first and second film thickness conditions described above is found to change little before and after aging for light with a wavelength of 400 nm, for example.

[0133] [Effects, etc.] As described above, the nitride semiconductor laser device 10 includes a stacked structure 100 made of a plurality of semiconductor layers (e.g., a first semiconductor layer 102, an active layer 103, and a second semiconductor layer 104) including a waveguide 110 and having a pair of opposing cavity facets (a front facet 100F and a rear facet 100R), and a dielectric multilayer film 150 disposed on at least one of the pair of cavity facets (the front facet 100F in this embodiment). The dielectric multilayer film 150 includes a first dielectric film 120, a second dielectric film 130, and a third dielectric film 140, in this order from the cavity facet side. The first dielectric film 120 is made up of n (n is a positive integer) layers of protective films, from a first protective film to an n-th protective film, in that order from the cavity facet side. In this embodiment, the first dielectric film 120 has n=4, and includes a first protective film 121, a second protective film 122, a third protective film 123, and a fourth protective film .

[0134] In the nitride semiconductor laser element 10, when the refractive index and film thickness of the kth (k is an integer satisfying 1≦k≦n) protective film in the first dielectric film 120 are nk and dk, respectively, the refractive index and film thickness of the second dielectric film 130 are ni and di, respectively, the refractive index and film thickness of the third dielectric film 140 are nj and dj, respectively, m1 is an integer equal to or greater than 2, and m2 is a positive integer, the nitride semiconductor laser element 10 satisfies the above formula (7), the above formula (8), and the above formula (6).

[0135] According to this, by appropriately combining the film thicknesses and refractive indices of the films included in the dielectric multilayer film 150 included in the nitride semiconductor laser device 10, it is possible to minimize variations in reflectivity even if the film thickness of the dielectric multilayer film 150 varies. This makes it possible to suppress variations in the optical output of the nitride semiconductor laser device 10 while it is operating, and to suppress deterioration of the nitride semiconductor laser device 10. In other words, the nitride semiconductor laser device 10 can suppress deterioration of its optical characteristics.

[0136] Alternatively, nitride semiconductor laser element 10 satisfies the above formula (7) and also satisfies the above formula (8). One of second dielectric film 130 and third dielectric film 140 has a property of being reduced in thickness by laser light 201 emitted from nitride semiconductor laser element 10, while the other has a property of being increased in thickness by laser light 201 emitted from nitride semiconductor laser element 10.

[0137] This also makes it possible to suppress fluctuations in reflectance even if the thickness of the dielectric multilayer film 150 varies, by appropriately combining the film thicknesses and refractive indices of the respective films in the dielectric multilayer film 150 included in the nitride semiconductor laser device 10. As a result, fluctuations in the optical output power of the nitride semiconductor laser device 10 during operation and deterioration of the nitride semiconductor laser device 10 can be suppressed.

[0138] Furthermore, for example, upon receiving laser light 201 emitted from the cavity end facet, a recess 131 is formed in the second dielectric film 130 and a protrusion 141 is formed in the third dielectric film 140 at the interface between the second dielectric film 130 and the third dielectric film 140.

[0139] This makes it possible to reduce the amount of change in the total film thickness of the dielectric multilayer film 150 even when irradiated with the laser light 201. Therefore, the change in the reflectance of the dielectric multilayer film 150 is further suppressed.

[0140] Furthermore, for example, the change in the film thickness of the second dielectric film 130 and the third dielectric film 140 occurs in the optical path of the laser light 201 emitted from the cavity end facet.

[0141] According to this, the change in the film thickness of the dielectric multilayer film 150 occurs on the optical path of the laser beam 201, so that the change in the total film thickness of the dielectric multilayer film 150 in the region through which the laser beam 201 passes is reduced. Therefore, the change in the reflectance of the dielectric multilayer film 150 is further suppressed.

[0142] Furthermore, for example, the third dielectric film 140 has an amorphous structure.

[0143] This provides the third dielectric film 140 with the property of increasing its thickness by absorbing the rare gas such as Ar contained in the second dielectric film 130, for example.

[0144] Furthermore, for example, the nitride semiconductor laser device 10 further satisfies the above-mentioned formula (9).

[0145] This makes it possible to reduce the amount of change in the total film thickness of the dielectric multilayer film 150 even when irradiated with the laser light 201. Therefore, the change in the reflectance of the dielectric multilayer film 150 is further suppressed.

[0146] Furthermore, for example, the oscillation wavelength of the nitride semiconductor laser device 10 is 420 nm or less.

[0147] As described above, the configuration of the dielectric multilayer film 150 is particularly effective as a facet coating film in a nitride semiconductor laser device 10 that emits laser light 201 at a wavelength of 420 nm or less, at which the dielectric multilayer film 150 is likely to absorb laser light 201.

[0148] Furthermore, for example, the nitride semiconductor laser device 10 emits laser light 201 of 1 W or more.

[0149] The change in the film thickness of the dielectric multilayer film 150 depends greatly on the optical output of the laser beam 201. For example, the change in the film thickness of the dielectric multilayer film 150 is noticeable when the laser beam 201 has an optical output of 1 W or more. Therefore, the configuration of the dielectric multilayer film 150 is particularly effective as a facet coating film in a nitride semiconductor laser device 10 that emits laser beam 201 of 1 W or more, which is likely to affect the film thickness of the dielectric multilayer film 150.

[0150] Furthermore, for example, the nitride semiconductor laser device 10 satisfies the above formula (10) when m3 is a positive integer.

[0151] This makes it possible to reduce the amount of change in the total film thickness of the dielectric multilayer film 150 even when irradiated with the laser light 201. Therefore, the change in the reflectance of the dielectric multilayer film 150 is further suppressed.

[0152] Moreover, for example, the second dielectric film 130 is one of Al2O3, Ta2O5, and ZrO2, and the third dielectric film 140 is one of SiO2, B2O3, P2O5, and GeO2.

[0153] This makes it possible to combine films in the dielectric multilayer film 150 that decrease in thickness and films that increase in thickness by absorbing the laser light 201. This makes it possible to suppress fluctuations in the optical output of the nitride semiconductor laser device 10 while it is being driven, and to suppress deterioration of the nitride semiconductor laser device 10.

[0154] Furthermore, for example, an aluminum oxynitride film is disposed between the cavity end facet and the dielectric multilayer film 150 .

[0155] This makes it possible for the aluminum oxynitride film to suppress oxidation of the cavity facets in the nitride semiconductor laser device 10. This also makes it possible to reduce dangling bonds in the cavity facets and the dielectric multilayer film 150. Therefore, for example, even when the nitride semiconductor laser device 10 is driven to produce a high optical output, deterioration of the dielectric multilayer film 150 can be suppressed.

[0156] Furthermore, for example, the aluminum oxynitride film contains crystalline aluminum nitride. In this case, the aluminum oxynitride film may be polycrystalline aluminum nitride, and may further be a film containing a large amount of oxygen in the grain boundaries of polycrystalline aluminum nitride.

[0157] This makes it possible to further suppress oxidation of the cavity facets in the nitride semiconductor laser device 10, since the aluminum oxynitride film contains crystals. This also makes it possible to further reduce dangling bonds in the cavity facets and the dielectric multilayer film 150. Therefore, even when the nitride semiconductor laser device 10 is driven to produce a high optical output, for example, deterioration of the dielectric multilayer film 150 can be further suppressed.

[0158] Furthermore, for example, a film made of at least one of aluminum silicon nitride, aluminum gallium nitride, aluminum yttrium nitride, aluminum lanthanum nitride, aluminum silicon oxynitride, aluminum gallium oxynitride, aluminum yttrium oxynitride, and aluminum lanthanum oxynitride is disposed between the resonator facet and the dielectric multilayer film.

[0159] This also makes it possible to suppress oxidation of the cavity facets in the nitride semiconductor laser device 10, similar to the aluminum oxynitride film. This also makes it possible to reduce dangling bonds in the cavity facets and the dielectric multilayer film 150. Therefore, even when the nitride semiconductor laser device 10 is driven to produce a high optical output, for example, deterioration of the dielectric multilayer film 150 can be suppressed.

[0160] (Other embodiments) Although the nitride semiconductor laser element according to the present disclosure has been described above based on the above-mentioned embodiments, the present disclosure is not limited to the above-mentioned embodiments. The present disclosure also includes configurations obtained by applying various modifications to the above-mentioned embodiments that would occur to those skilled in the art, and configurations realized by arbitrarily combining the components and functions of the above-mentioned embodiments within the scope of the present disclosure. [Industrial Applicability]

[0161] The nitride semiconductor laser element of the present disclosure can be used, for example, as a light source for industrial laser equipment such as industrial lighting, facility lighting, vehicle headlamps, and laser processing machines, as well as for image display devices such as laser displays and projectors. [Explanation of symbols]

[0162] 10. Nitride semiconductor laser device 100 Laminated structure 100a First conductivity type semiconductor layer 100b Second conductivity type semiconductor layer 100F Front end face 100R rear end face 101 Substrate 102 first semiconductor layer 103 Active layer 104 Second semiconductor layer 105 Contact layer 106 Insulating layer 107 Second electrode 108 Pad electrode 109 1st electrode 110 Waveguide 120 First dielectric film 121 1st protective film 122 Second protective film 123 Third protective film 124 4th protective film 130 Second dielectric film 131 recess 140 Third dielectric film 141 Convex part 150 Dielectric multilayer film 160 Coating Film 200 optical axis 201 Laser light 300, 301, d1, d2, d3, d4, di, dj film thickness 400~408, 410~413, 420~423, 430, 450 dashed line 440~443 Intersection 460, 461 position

Claims

1. a laminated structure including a plurality of semiconductor layers including a waveguide and having a pair of cavity end faces facing each other; a dielectric multilayer film disposed on at least one of the pair of cavity end faces, the dielectric multilayer film has a first dielectric film, a second dielectric film, and a third dielectric film in this order from the cavity end face side, the first dielectric film is composed of n layers of protective films, from a first protective film to an nth protective film (n is a positive integer), in order from the cavity end face side, The refractive index and thickness of the kth (k is an integer satisfying 1≦k≦n) protective film in the first dielectric film are defined as nk and dk, respectively; The refractive index and thickness of the second dielectric film are defined as ni and di, respectively; The refractive index and film thickness of the third dielectric film are denoted by nj and dj, respectively; m1 is an integer of 2 or more, When m2 is a positive integer, [Equation 1] and nj × dj = m2 × λ / 4 ± λ / 16 Fulfilling If m3 is a positive integer, then [Equation 2] Fulfilling No dielectric film is provided on the surface of the third dielectric film opposite to the surface on which the second dielectric film is located. Nitride semiconductor laser element.

2. At the interface between the second dielectric film and the third dielectric film, the second dielectric film has a recess; The third dielectric film has a protrusion.

2. The nitride semiconductor laser device according to claim 1.

3. The recess and the protrusion are positioned in the optical path of the laser light emitted from the cavity end face.

3. The nitride semiconductor laser device according to claim 2.

4. The third dielectric film has an amorphous structure.

4. The nitride semiconductor laser device according to claim 1.

5. moreover, 3λ / 16≦nj×dj≦5λ / 16 fulfill 5. The nitride semiconductor laser device according to claim 1.

6. The oscillation wavelength of the nitride semiconductor laser element is 420 nm or less.

6. The nitride semiconductor laser device according to claim 1.

7. The nitride semiconductor laser element emits laser light of 1 W or more.

7. The nitride semiconductor laser device according to claim 1.

8. The second dielectric film is Al ２ O ３ , Ta ２ O ５ , and ZrO ２ Either The third dielectric film is made of SiO ２ , B ２ O ３ , P ２ O ５ , and GeO ２ Either 8. The nitride semiconductor laser device according to claim 1.

9. An aluminum oxynitride film is disposed between the cavity end facet and the dielectric multilayer film.

9. The nitride semiconductor laser device according to claim 1.

10. The aluminum oxynitride film contains crystalline aluminum nitride. The nitride semiconductor laser device according to claim 9 .

11. Between the cavity end facet and the dielectric multilayer film, A film made of at least one of aluminum silicon nitride, aluminum gallium nitride, aluminum yttrium nitride, aluminum lanthanum nitride, aluminum silicon oxynitride, aluminum gallium oxynitride, aluminum yttrium oxynitride, and aluminum lanthanum oxynitride is disposed.

11. The nitride semiconductor laser device according to claim 1.

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