Nitride semiconductor laser element

Abstract

A nitride semiconductor laser element (10) comprises a layered structure (100) and a dielectric multilayer film (150). The dielectric multilayer film (150) has a first dielectric film (120), a second dielectric film (130), and a third dielectric film (140) in this order from a resonator end face side. The nitride semiconductor laser element (10) satisfies (I), satisfies nj×dj=m2×λ / 4±λ / 16, and satisfies (II).

Description

Technical Field

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

Background Art

[0002] Conventionally, in a semiconductor laser device that emits laser light, reflection films are formed on end faces (front end face and rear end face) in order to resonate the laser light inside the semiconductor laser device and to appropriately emit the resonated laser light from the semiconductor laser device (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The reflection film formed on the end face of the semiconductor laser device may be deformed by absorbing the laser light from the semiconductor laser device. When the reflection film is deformed, optical characteristics such as the transmittance and reflectance of the laser light change.

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

Means for Solving the Problems

[0006] A nitride semiconductor laser device according to one aspect of the present disclosure includes a stacked structure composed of a plurality of semiconductor layers including a waveguide and having a pair of resonator end faces facing each other, and a dielectric multilayer film disposed on at least one of the pair of resonator 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 resonator end face side. The first dielectric film is composed of n (n is a positive integer) layers of protective films from a first protective film to an nth protective film in order from the resonator end face side. The refractive index and film thickness of the kth (k is an integer satisfying 1≦k≦n) protective film in the first dielectric film are denoted as nk and dk, respectively. The refractive index and film thickness of the second dielectric film are denoted as ni and di, respectively. The refractive index and film thickness of the third dielectric film are denoted as nj and dj, respectively. When m1 is an integer of 2 or more and m2 is a positive integer,

Equation

Equation

[0007] Also, a nitride semiconductor laser device according to another aspect of the present disclosure includes a stacked structure composed of a plurality of semiconductor layers including a waveguide and having a pair of resonator end faces facing each other, and a dielectric multilayer film disposed on at least one of the pair of resonator 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 resonator end face side. The first dielectric film is composed of n (n is a positive integer) layers of protective films from a first protective film to an nth protective film in order from the resonator end face side. The refractive index and film thickness of the kth (k is an integer satisfying 1≦k≦n) protective film in the first dielectric film are denoted as nk and dk, respectively. The refractive index and film thickness of the second dielectric film are denoted as ni and di, respectively. The refractive index and film thickness of the third dielectric film are denoted as nj and dj, respectively. When m1 is an integer of 2 or more and m2 is a positive integer,

Equation

Effect of the Invention

[0008] According to the present disclosure, a nitride semiconductor laser element capable of suppressing changes in optical characteristics can be provided.

Brief Description of the Drawings

[0009]

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[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that each of the embodiments described below shows a specific example of the present disclosure. Therefore, the numerical values, shapes, materials, components, and the arrangement positions and connection forms of the components shown in the following embodiments are merely examples and are not intended to limit the present disclosure.

[0011] Also, each figure is a schematic diagram and is not necessarily drawn precisely. Therefore, the scales and the like in each figure do not necessarily match. In each figure, the same reference numerals are given to substantially the same configurations, and redundant descriptions are omitted or simplified.

[0012] In this specification, the terms "upper" and "lower" do not refer to the upward direction (vertically upward) and the downward direction (vertically downward) in absolute spatial recognition, but are used as terms defined by the relative positional relationship based on the stacking order in the stacked structure. Also, the terms "upper" and "lower" are applicable not only when two components are arranged at intervals and there is another component between the two components, but also when the two components are arranged in contact with each other.

[0013] In this specification and the drawings, the X-axis, Y-axis, and Z-axis represent the three axes of a three-dimensional orthogonal coordinate system. In each embodiment, the Z-axis direction is the vertical direction, and the direction perpendicular to the Z-axis (the direction parallel to the XY plane) is the horizontal direction. Note that the positive direction of the Z-axis is vertically upward.

[0014] (Embodiment) [Overview] FIG. 1 is a schematic cross-sectional view showing the configuration of a nitride semiconductor laser element 10 according to an embodiment. FIG. 2 is a cross-sectional view schematically showing an example of the deformation of a dielectric film when the nitride semiconductor laser element 10 according to the embodiment emits laser light 201. Note that FIGS. 1 and 2 are cross-sectional views taken along line I-I of FIG. 4 described later.

[0015] The nitride semiconductor laser element 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 that emits laser light 201 sandwiched between the first conductivity type semiconductor layer 100a and the second conductivity type semiconductor layer 100b. A dielectric multilayer film 150 is formed on the front end face 100F of the nitride semiconductor laser element 10 in order to resonate the laser light 201 inside the stacked structure 100 and effectively emit it from the front end face 100F. The dielectric multilayer film 150 is composed of, 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 face 100F of the stacked structure 100.

[0016] The first dielectric film 120 is a film that protects the front end face 100F and suppresses the 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 films for adjusting the reflectivity, respectively.

[0017] The first dielectric film 120, the second dielectric film 130, and the third dielectric film 140 are formed on the front end face 100F with substantially uniform film thicknesses.

[0018] Conventionally, when designing the reflectivity of the dielectric multilayer film 150, it was not necessary to consider 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 as to be maximum or minimum with respect to the oscillation wavelength of the laser light 201 emitted from the stacked structure 100.

[0019] In recent years, there is a blue-violet high-output laser element having an oscillation wavelength of about 405 nm and a light output of the laser light 201 of 1 W or more. The inventors of the present application have found that in such a blue-violet high-output laser element, when aging is performed for a long time (that is, when the laser light 201 is continuously emitted), the film of the dielectric multilayer film 150 near the portion (light-emitting point) where the laser light 201 is emitted on the front end face 100F deteriorates.

[0020] 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 laminate structure 100.

[0021] For example, by emitting the laser light 201 from the laminate structure 100, the respective film thicknesses of the second dielectric film 130 and the third dielectric film 140 are different between the film thickness 300 of the portion through which the laser light 201 passes and the film thickness 301 of the portion through which the laser light 201 does not pass. That is, the respective film thicknesses 300 and 301 of the second dielectric film 130 and the third dielectric film 140 change by emitting the laser light 201 from the laminate structure 100.

[0022] FIG. 3 is a graph showing the reflectance of the dielectric multilayer film with respect to the wavelength of the nitride semiconductor laser device according to the comparative example. The nitride semiconductor laser device according to the comparative example is the same as the nitride semiconductor laser device 10 according to the embodiment except for the material, film thickness, and refractive index employed for the dielectric multilayer film. Further, the reflectance before aging shown in FIG. 3 is, for example, the reflectance of light in a state where it is not deformed by the laser light 201, such as the dielectric multilayer film 150 shown in FIG. 1. On the other hand, the reflectance after aging shown in FIG. 3 is, for example, the reflectance of light in a state where it is deformed by the laser light 201, such as the dielectric multilayer film 150 shown in FIG. 2.

[0023] As shown in FIG. 3, the position of the peak located around 400 nm in wavelength is different between the reflectance before aging and the reflectance after aging. Specifically, the reflectance of the dielectric multilayer film according to the comparative example causes the reflectance of the peak located around 400 nm in wavelength to increase by about 1.5% by absorbing the laser light. Therefore, the nitride semiconductor laser device according to the comparative example has different optical characteristics (specifically, light output) before and after aging. Thus, for example, if the nitride semiconductor laser device 10 is continuously used, the optical characteristics change over time.

[0024] As a result of intensive studies, the inventors of the present application have found that by appropriately setting the material, film thickness, refractive index, etc. of the dielectric multilayer film 150 included in the nitride semiconductor laser element 10, changes in optical characteristics can be suppressed. Specifically, the inventors of the present application have found that there are films with increasing film thickness and decreasing film thickness during aging. Therefore, the inventors of the present application have found that by appropriately combining the films with increasing film thickness and decreasing film thickness during aging, changes in reflectance can be suppressed even when the film thickness changes during aging.

[0025] Hereinafter, the configuration and optical characteristics of the nitride semiconductor laser element 10 according to the embodiment will be specifically described.

[0026] In the following description, emitting the laser light 201 from the stacked structure 100 is also simply referred to as aging.

[0027] [Configuration] With reference to FIGS. 1 and 4, the configuration of the nitride semiconductor laser element 10 will be described.

[0028] FIG. 4 is a cross-sectional view showing the nitride semiconductor laser element 10 according to the embodiment taken along the line IV-IV of FIG. 1.

[0029] The nitride semiconductor laser element 10 is a nitride semiconductor light-emitting element that emits laser light 201.

[0030] The nitride semiconductor laser element 10 includes a stacked structure 100 and a dielectric multilayer film 150.

[0031] The stacked structure 100 is a stack composed of a plurality of semiconductor layers including a waveguide 110. The stacked structure 100 also has a front-side end face 100F and a rear-side end face 100R, which are a pair of resonator end faces facing each other. The dielectric multilayer film 150 is disposed on at least one of the pair of resonator end faces. In the present embodiment, the dielectric multilayer film 150 is disposed on the front-side end face 100F.

[0032] 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. In FIG. 1, the insulating layer 106, the second electrode 107, the pad electrode 108, and the first electrode 109 are not shown. In the present embodiment, the stacked structure 100 is formed of a gallium nitride-based material which is an example of a nitride material. Thereby, for example, by setting the input current to the stacked structure 100 to be 2 A or more and 10 A or less, and the input voltage to be 4 V or more and 6 V or less, a laser beam 201 having a wavelength in a band of about 390 nm or more and 420 nm or less and an optical output of about 3 W or more and 10 W or less can be realized. Thus, in the present embodiment, the nitride semiconductor laser element 10 emits a laser beam 201 of 1 W or more. Further, the oscillation wavelength of the nitride semiconductor laser element 10 is 420 nm or less. More specifically, the stacked structure 100 emits a laser beam 201 having a peak wavelength of 400 nm.

[0033] Also, for example, the optical density of the laser beam 201 is 0.1 W / μm or more. Note that the optical density is the optical output of the laser beam 201 / stripe width. The stripe width here is, for example, the lateral width of a ridge portion (the length in the X-axis direction in the present embodiment) described later. The width of the ridge portion (hereinafter also referred to as the stripe width) is, for example, about 30 μm or more and 100 μm or less.

[0034] The resonator length of the stacked structure 100 (the length in the Y-axis direction in the present embodiment) is, for example, 1200 μm or more and 5000 μm or less.

[0035] Note that the optical characteristics of the nitride semiconductor laser element 10 are not limited to the above. For example, the nitride semiconductor laser element 10 may have optical characteristics such that when the input current to the stacked structure 100 is 2 A or more and 10 A or less, and the input voltage is 3.5 V or more and 6 V or less, it emits laser light 201 having a wavelength in a band of about 365 nm or more and 390 nm or less, and the optical output is about 1 W or more and 5 W or less. In this case, for example, the stripe width is about 8 μm or more and 100 μm or less. Also, in this case, for example, the resonator length of the stacked structure 100 is, for example, 800 μm or more and 5000 μm or less.

[0036] The substrate 101 is a plate-shaped member that serves as the base material of the stacked structure 100. In the present embodiment, the substrate 101 is a GaN single crystal substrate with a thickness of 100 μm. Note that the thickness of the substrate 101 is not limited to 100 μm, and may be, for example, 50 μm or more and 120 μm or less. Also, the material forming the substrate 101 is not limited to GaN single crystal, and may be sapphire, SiC, or the like.

[0037] The first semiconductor layer 102 is a first-conductive-type semiconductor layer disposed above the substrate 101. In the present 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.

[0038] The active layer 103 is a light-emitting layer disposed above the first semiconductor layer 102. In the present embodiment, the active layer 103 is a quantum well active layer in which a well layer made of InGaN and a barrier layer made of GaN are alternately stacked, and has two well layers. By providing such an active layer 103, the nitride semiconductor laser element 10 can emit blue laser light with a wavelength of about 400 nm. The configuration of the active layer 103 is not limited to this, and any quantum well active layer in which a well layer and a barrier layer are alternately stacked may be used. Note that the active layer 103 may include a guide layer formed on at least one of the upper and lower sides of the quantum well active layer.

[0039] 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 the present embodiment, the second semiconductor layer 104 is a p-type semiconductor layer and includes a p-type clad layer. The p-type clad layer is a superlattice layer in which 100 layers each of a layer made of p-AlGaN and a layer made of GaN with a thickness of 3 nm are alternately stacked. Note that the configuration of the p-type clad layer is not limited to this.

[0040] A waveguide 110, which is a waveguide portion of the laser light 201, is formed by the first semiconductor layer 102, the active layer 103, and the second semiconductor layer 104.

[0041] The waveguide 110 is a portion where the laser light 201 is guided inside the stacked structure 100. The waveguide 110 is composed 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.

[0042] The contact layer 105 is a semiconductor layer of a second conductivity type that makes an ohmic contact with the second electrode 107. In the present embodiment, the contact layer 105 is a p-type semiconductor layer and is a layer made of p-GaN. Note that the configuration of the contact layer 105 is not limited to this.

[0043] Also, in the present 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 (that is, a region of the active layer 103 located below the ridge portion) serves as a light-emitting point and emits the laser light 201.

[0044] The first electrode 109 is an electrode disposed on the main surface below the substrate 101 (that is, the main surface on which the first semiconductor layer 102 and the like are not disposed). The first electrode 109 is, for example, a stacked film in which Ti, Pt, and Au are stacked in this order from the substrate 101 side. The configuration of the first electrode 109 is not limited to this.

[0045] The second electrode 107 is an electrode disposed on the contact layer 105. In the present embodiment, the second electrode 107 is a p-side electrode that makes an ohmic contact with the contact layer 105. A pad electrode 108 is disposed on the p-side electrode.

[0046] 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.

[0047] 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.

[0048] Although not shown in FIG. 4, the laminated structure 100 may further include an insulating film such as an SiO2 film that covers the side walls of the ridge portion and the like in addition to the above-described layers.

[0049] In the present embodiment, the laminated structure 100 is a so-called single emitter having one ridge portion (emitter), but may also be a so-called multi-emitter having a plurality of (for example, about 60) ridge portions. 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 laminated structure 100 is about 100 W or more and 200 W or less.

[0050] The dielectric multilayer film 150 is a protective film disposed on the front-side end face 100F of the laminated structure 100. Specifically, the dielectric multilayer film 150 protects the front-side end face 100F of the laminated structure 100 and reduces the reflectance of the laser light 201 at the front-side end face 100F. 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 resonator end face (the front-side end face 100F in the present embodiment) side.

[0051] The first dielectric film 120 is a dielectric layer disposed on the front end surface 100F side among the first dielectric film 120, the second dielectric film 130, and the third dielectric film 140. 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. Thereby, oxygen diffusion from the outside of the dielectric multilayer film 150 to the stacked structure 100 can be reduced. For this reason, deterioration of the front end surface 100F of the stacked structure 100 can be suppressed. Therefore, long-term operation of the nitride semiconductor laser element 10 becomes possible.

[0052] Further, the first dielectric film 120 is directly connected to the front end surface 100F of the stacked structure 100. That is, the first dielectric film 120 is formed in contact with the front end surface 100F. For this reason, 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 surface 100F can be enhanced.

[0053] For example, the first dielectric film 120 is composed of n (n is a positive integer) layers of protective films from the first protective film to the nth protective film in order from the front end surface 100F side. In the present embodiment, n = 4 for the first dielectric film 120, and it has a first protective film 121, a second protective film 122, a third protective film 123, and a fourth protective film 124.

[0054] The first protective film 121 is a dielectric film disposed on the front end surface 100F side among the plurality of protective films included in the first dielectric film 120. In the present embodiment, the first protective film 121 is a film including a SiN film. More specifically, the first protective film 121 is a film made of a SiN film having a thickness d1 of about 0.5 nm. Note that the configuration of the first protective film 121 is not limited to this. The first protective film 121 may be another oxynitride film such as SiON, for example.

[0055] The second protective film 122 is a dielectric film laminated on the first protective film 121. In the present embodiment, the second protective film 122 is a film containing an AlON film. More specifically, the second protective film 122 is a film made of an AlON film with a thickness d2 of about 21 nm. Note that 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.

[0056] The third protective film 123 is a dielectric film laminated on the second protective film 122. In the present embodiment, the third protective film 123 is a film made of an Al2O3 film with a thickness d3 of about 13 nm. Note that the configuration of the third protective film 123 is not limited to this. The third protective film 123 may be, for example, another dielectric film such as SiO2.

[0057] 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 the present embodiment, the fourth protective film 124 is a film made of an AlON film with a thickness d4 of about 11 nm. Note that 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.

[0058] The second dielectric film 130 is a dielectric film laminated outside the first dielectric film 120. In the present embodiment, the second dielectric film 130 is an Al2O3 film with a thickness di of about 167 nm.

[0059] The third dielectric film 140 is a dielectric film laminated outside the second dielectric film 130. In the present embodiment, the third dielectric film 140 is a SiO2 film with a thickness dj of about 58 nm.

[0060] Figure 5 is a table showing the change in film thickness with respect to the aging conditions. Note that in both Condition 1 and Condition 2, the peak wavelength (oscillation wavelength) of the laser beam 201 is 405 nm.

[0061] As shown in Condition 1 of Fig. 5, when a laser beam 201 of 4.5 W was emitted from the laminated structure 100 at 25°C for 736 h, the rate of change in the film thickness of the second dielectric film 130 made of an Al2O3 film had variations in the light intensity distribution of the laser beam 201, with a maximum of -8.5% and a minimum of -6.2%. Also, 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 by 3 .7% at minimum.

[0062] Note that the optical density under Condition 1 was 0.15 (W / μm).

[0063] Also, as shown in Condition 2 of Fig. 5, when a laser beam 201 of 1 W was emitted from the laminated structure 100 at 25°C for 4500 h, the rate of change in the film 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 film thickness of the third dielectric film 140 made of an SiO2 film was +5.2% at maximum and by 4 .0% at minimum.

[0064] Note that the optical density under Condition 2 was 0.149 (W / μm).

[0065] The average rate of change in the film thickness of the second dielectric film 130 made of an Al2O3 film under Conditions 1 and 2 was -7.6%. Also, the average rate of change in the film thickness of the third dielectric film 140 made of an SiO2 film under Conditions 1 and 2 was +4.6%.

[0066] Also, the rate of change in the film thickness of the second dielectric film 130 made of an Al2O3 film decreased rapidly within an aging time of 1000 h when the optical density was about 0.15 W / μm, and gradually decreased while the change became gentle after the aging time exceeded 1000 h. Also, the rate of change in the film thickness of the third dielectric film 140 made of an SiO2 film increased rapidly within an aging time of 1000 h when the optical density was about 0.15 W / μm, and gradually increased while the change became gentle after the aging time exceeded 1000 h.

[0067] As described above, the second dielectric film 130 made of an Al2O3 film contracts due to aging, and its film thickness decreases. The film made of an Al2O3 film is amorphous and contains several percent of Ar in the as-deposited state (as-depo.). However, it is considered that the film made of the as-depo. Al2O3 film contracts and its film thickness decreases due to the desorption of Ar due to the optical load during aging.

[0068] On the other hand, the third dielectric film 140 made of an SiO2 film expands due to aging, and its film thickness increases. It is considered that the third dielectric film 140 made of an SiO2 film expands and its film thickness increases because Ar contained in the second dielectric film 130 made of an Al2O3 film desorbs and diffuses into the SiO2 film.

[0069] From this, as materials whose films expand due to aging, materials with a stable amorphous state and materials with freedom in molecular bonding and likely to contain impurity atoms inside can be considered. Examples of such materials include SiO2, B2O3, P2O5, and GeO2. In the present 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.

[0070] Also, as materials whose films contract due to aging, materials with a more stable crystalline state than the amorphous state and materials with strong interatomic bonding and difficult to contain impurity atoms inside can be considered. Examples of such materials include Al2O3, Ta2O5, and ZrO2. For example, the second dielectric film 130 is any one of Al2O3, Ta2O5, and ZrO2.

[0071] Thus, one of the second dielectric film 130 and the third dielectric film 140 has a property that its film thickness decreases due to the laser light 201 emitted from the nitride semiconductor laser element 10. The other has a property that its film thickness increases due to the laser light 201 emitted from the nitride semiconductor laser element 10. In the present embodiment, the second dielectric film 130 has a property that its film thickness decreases due to the laser light 201 emitted from the nitride semiconductor laser element 10. The third dielectric film 140 has a property that its film thickness increases due to the laser light 201 emitted from the nitride semiconductor laser element 10. Specifically, upon receiving the laser light 201 emitted from the front end face 100F, at the interface between the second dielectric film 130 and the third dielectric film 140, a concave portion 131 is formed in the second dielectric film 130, and a convex portion 141 is formed in the third dielectric film 140. Further, 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 of the laser light 201 emitted from the front end face 100F (for example, on the optical axis 200 of the laser light 201).

[0072] According to the nitride semiconductor laser element 10 including the dielectric multilayer film 150 composed of such a material, since the dielectric multilayer film 150 has a film thickness and a refractive index as described below, even when the laser light 201 is emitted for about 10,000 h, the reduction rate of the optical output is 20% or less.

[0073] Note that a coating film 160 may be disposed between the front end face 100F and the dielectric multilayer film 150.

[0074] The coating film 160 is a film that protects the 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.

[0075] Note that 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. Also, the above-mentioned materials may be used for the material of the first dielectric film 120.

[0076] Further, such a dielectric multilayer film 150 has a film thickness and a refractive index as described later, so that, for example, the reflectance with respect to light having a wavelength of 400 nm is about 4% or more and 20% or less. Also, by adopting the so-called AR (Anti Reflection) coating technology for the dielectric multilayer film 150, the reflectance of the dielectric multilayer film 150 with respect to light having a wavelength of 400 nm may be 0.1% or less.

[0077] Also, the dielectric multilayer film 150 may be provided on the rear end face 100R.

[0078] [Optical Characteristics] Subsequently, the optical characteristics of the nitride semiconductor laser element 10 according to the embodiment will be described.

[0079] The inventors of the present application performed optical simulations in order to determine conditions under which the change in reflectance is small 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.

[0080] FIG. 6A is a graph showing the reflectance with respect to the film thickness before aging of the dielectric multilayer film 150 included in the nitride semiconductor laser element 10 according to the embodiment. FIG. 6B is a graph showing the reflectance with respect to the film thickness after aging of the dielectric multilayer film 150 included in the nitride semiconductor laser element 10 according to the embodiment. FIG. 6C is a graph showing the amount of change in the reflectance with respect to the film thickness before and after aging of the dielectric multilayer film 150 included in the nitride semiconductor laser element 10 according to the embodiment.

[0081] In FIGS. 6A to 6C, the conditions such as the film thickness and refractive index of the first dielectric film 120 are fixed. Further, in FIGS. 6A to 6C, the second dielectric film 130 is an Al2O3 film, and the third dielectric film 140 is an SiO2 film. In FIGS. 6A to 6C, the film thicknesses of these films are changed in the range of 0 nm to 300 nm, the reflectance is calculated, and a contour display is performed.

[0082] Note that the film thickness shown in FIG. 6B indicates the film thickness before aging. Specifically, the graph shown in FIG. 6B shows the reflectance when the film thickness of the second dielectric film 130 is -7.6% and the film thickness of the third dielectric film 140 is +4.6% with respect to the film thickness before aging in the second dielectric film 130 and the third dielectric film 140, and a contour display is performed.

[0083] Further, FIG. 6C shows the calculation result of the difference in reflectance before and after aging. Specifically, the graph shown in FIG. 6C shows the value obtained by subtracting the reflectance of the graph shown in FIG. 6B from the reflectance of the graph shown in FIG. 6A.

[0084] In FIG. 6C, for the amount of change on the plus side of the reflectance, contour lines are shown in steps of +3% in order from +1.5%, and for the amount of change on the minus side of the reflectance, contour lines are shown in steps of -3% in order from -1.5%.

[0085] It can be seen from FIG. 6C that there is a region where the amount of change in the reflectance is -1.5% or more and +1.5% or less before and after aging.

[0086] FIG. 7 is a diagram for explaining the relationship between the film thicknesses of the second dielectric film 130 and the third dielectric film 140 and the reflectance of the dielectric multilayer film 150. Note that the graph showing the reflectance with respect to the film thickness shown in FIG. 7 is the same as that in FIG. 6A.

[0087] One or more protective films (in this embodiment, four protective films) in the first dielectric film 120 are defined as n layers of films, namely the first protective film, the second protective film, ···, and the nth protective film, from the front end face 100F side in order. Let the refractive index and film thickness of the kth (where k is a positive integer) protective film be nk and dk, respectively, the refractive index and film thickness of the second dielectric film 130 be ni and di, respectively, and the refractive index and film thickness of the third dielectric film 140 be nj and dj, respectively. When the total optical film thickness of one or more protective films in the first dielectric film 120 is A, the following formula (1) is satisfied.

[0088]

Equation

[0089] Also, the dashed lines 400 to 407 shown in FIG. 7 satisfy the following formula (2) in order from the left side of the paper surface.

[0090] A = m1 × λ / 4 Formula (2)

[0091] Here, m1 is a positive integer. For example, the dashed line 400 is a straight line when m1 = 1 is substituted into formula (2). Similarly, for example, the dashed line 401 is a straight line when m1 = 2 is substituted into formula (2). Similarly, for example, the dashed line 402 is a straight line when m1 = 3 is substituted into formula (2). Similarly, for example, the dashed line 403 is a straight line when m1 = 4 is substituted into formula (2). Similarly, for example, the dashed line 404 is a straight line when m1 = 5 is substituted into formula (2). Similarly, for example, the dashed line 405 is a straight line when m1 = 6 is substituted into formula (2). Similarly, for example, the dashed line 406 is a straight line when m1 = 7 is substituted into formula (2). Similarly, for example, the dashed line 407 is a straight line when m1 = 8 is substituted into formula (2).

[0092] Here, the reflectance of the dielectric multilayer film 150 takes a maximum value when m1 is an even number and a minimum value when m1 is an odd number.

[0093] In addition, the change between the maximum and minimum of the reflectance in the dielectric multilayer film 150 coincides with the period of cos(4π×nj×dj / λ), which is the proportional term of the film thickness in the relational expression between the optical film thickness and the reflectance of the SiO2 film, which is the third dielectric film 140, derived from Fresnel's formula. That is, the multiplication of the film thickness and the refractive index of the third dielectric film 140 (that is, the optical film thickness) at which the reflectance of the dielectric multilayer film 150 becomes maximum or minimum satisfies the following formula (3).

[0094] B = nj×dj = N1×λ / 4 Formula (3)

[0095] Note that optical the refractive index and the film thickness of the third dielectric film 140 are nj and dj, respectively. Also, N1 is 0 or a positive integer. For example, when N1 = 1, B becomes the dashed line 410. Also, for example, when N1 = 2, B becomes the dashed line 411. Also, for example, when N1 = 3, B becomes the dashed line 412. Also, for example, when N1 = 4, B becomes the dashed line 413.

[0096] The above formula (3) is satisfied even when the film thickness of the first dielectric film 120 is changed.

[0097] On the other hand, although the period between the maximum and minimum of the relationship between the optical film thickness and the reflectance of the second dielectric film 130 is λ / 4, the optical film thickness at which the maximum or minimum occurs is affected by the film thickness of the first dielectric film 120, and thus is not necessarily an integer multiple of λ / 4.

[0098] Here, when the total optical film thickness of the first dielectric film 120 and the second dielectric film 130 is D, the following formula (4) is satisfied.

[0099]

Equation

[0100] In addition, the film thickness and refractive index of the second dielectric film 130 at which the reflectance of the dielectric multilayer film 150 becomes maximum or minimum satisfy the following formula (5).

[0101] D = N2 × λ / 4 Formula (5)

[0102] Note that the refractive index and film thickness of the second dielectric film 130 are ni and di, respectively. Also, N2 is a positive integer. For example, when N2 = 1, D becomes the dashed line 420. Also, for example, when N2 = 2, B becomes the dashed line 421. Also, for example, when N2 = 3, B becomes the dashed line 422. Also, for example, when N2 = 4, B becomes the dashed line 423. Also, for example, when N2 = 5, B becomes the dashed line 424.

[0103] The above formula (5) is satisfied even when the ratio of the film thickness of the first dielectric film 120 to the film thickness of the second dielectric film 130 is changed.

[0104] Subsequently, the change in film thickness when the film thickness of the first dielectric film 120 is changed will be described.

[0105] Figures 8A to 8F are graphs showing the reflectance with respect to the film thickness before aging of the dielectric multilayer film 150 included in the nitride semiconductor laser element 10 according to the embodiment. Figures 9A to 9F are graphs showing the amount of change in reflectance with respect to the film thickness before and after aging of the dielectric multilayer film 150 included in the nitride semiconductor laser element 10 according to the embodiment.

[0106] Note that FIGS. 8A and 9A are graphs when the optical film thickness of the first dielectric film 120 is λ / 8. FIGS. 8B and 9B are graphs when the optical film thickness of the first dielectric film 120 is 3×λ / 16. FIGS. 8C and 9C are graphs when the optical film thickness of the first dielectric film 120 is λ / 4. FIGS. 8D and 9D are graphs when the optical film thickness of the first dielectric film 120 is 5×λ / 16. FIGS. 8E and 9E are graphs when the optical film thickness of the first dielectric film 120 is 3×λ / 8. FIGS. 8F and 9F are graphs when the optical film thickness of the first dielectric film 120 is λ / 2.

[0107] Note that λ represents the oscillation wavelength of the laser beam 201, and in the present embodiment, it is 400 nm.

[0108] Also, in FIGS. 9A to 9F, contour lines are shown in increments of +3% in order from +1.5% for the change amount on the plus side of the reflectance, and contour lines are shown in increments of -3% in order from -1.5% for the change amount on the minus side of the reflectance.

[0109] As shown in FIGS. 9B, 9C, and 9D, it can be seen that within the broken line 430, the change amount of the reflectance is about -1.5% or more and +1.5% or less. The broken line 430 indicates a range where the film thickness of the second dielectric film 130 is 3×λ / 4 or less and the film thickness of the third dielectric film 140 is 3×λ / 4 or less.

[0110] From the above, by setting the optical film thickness of the first dielectric film 120 (more specifically, the total optical film thickness of the plurality of protective films included in the first dielectric film 120) to be 3×λ / 16 or more and 5×λ / 16 or less, the optical film thickness of the second dielectric film 130 to be 3×λ / 4 or less, and the optical film thickness of the third dielectric film 140 to be 3×λ / 4 or less, even when aging occurs, the change amount of the reflectance of the dielectric multilayer film 150 can be made small to be about -1.5% or more and +1.5% or less. That is, the first dielectric film 120 satisfies the following formula (6).

[0111]

Equation

[0112] 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.

[0113] When a plurality of nitride semiconductor laser elements 10 having the dielectric multilayer film 150 formed thereon are manufactured, even if an attempt is made to manufacture the dielectric multilayer film 150 with the same film thickness, due to manufacturing variations, the film thicknesses of the respective dielectric multilayer films 150 of the plurality of nitride semiconductor laser elements 10 do not completely match.

[0114] 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. Note that the graph showing the reflectance with respect to the film thickness shown in FIG. 10 is the same as that in FIG. 6A.

[0115] At the maximum value, minimum value, and saddle point of the reflectance in the graph shown in FIG. 10, it is considered that the change in the reflectance with respect to the change in the film thickness of the dielectric multilayer film 150 is small, that is, stable. The maximum value, minimum value, and saddle point of the reflectance in the graph shown in FIG. 10 are the intersections 440 to 443 of any one of the broken lines 400 to 404 shown in FIG. 10 and any one of the broken lines 410 to 413. In other words, the maximum value, minimum value, and saddle point of the reflectance in the graph shown in FIG. 10 are the film thicknesses that satisfy the above-described formula (1) and the above-described formula (3).

[0116] For example, when A in the above-described formula (1) is an even number and B in the above-described formula (3) is an even number, the reflectance shows a maximum and becomes one of the plurality of intersections 440. Further, for example, when A in the above-described formula (1) is an even number and B in the above-described formula (3) is an odd number, the reflectance shows a saddle point and becomes one of the plurality of intersections 441. For example, when A in the above-described formula (1) is an odd number and B in the above-described formula (3) is an even number, the reflectance shows a saddle point and becomes one of the plurality of intersections 442. For example, when A in the above-described formula (1) is an odd number and B in the above-described formula (3) is evenIn this case, the reflectance shows a minimum and becomes one of the plurality of intersection points 443.

[0117] Here, as the reflectance of the dielectric multilayer film 150, in order to achieve a high reflectance, it is good to select the intersection point 440 or 443, and in order to achieve a low reflectance, it is good to select the intersection point 441 or 442.

[0118] As described above, in the vicinity of the intersection points 440 to 443, the change in reflectance with respect to the change in the film thickness of the dielectric multilayer film 150 can be made small. For example, within the range of the region surrounded by the broken line 450 of the parallelogram indicating the vicinity of the intersection points 440 to 443, the change in reflectance with respect to the change in the film thickness of the dielectric multilayer film 150 can be made small. The region surrounded by such a broken line 450 satisfies the following formulas (7) and (8).

[0119]

Equation

[0120] B1 = nj × dj = m2 × λ / 4 ± λ / 16 Formula (8)

[0121] Note that both m1 and m2 are positive integers.

[0122] By setting such a second film thickness condition, the change in reflectance with respect to the change in the film thickness of the dielectric multilayer film 150 can be made small. Also, by setting m1 as an integer of 2 or more, the change in reflectance with respect to the change in the film thickness of the dielectric multilayer film 150 can be made even smaller. Further, for example, when m2 = 1, in other words, by setting the following formula (9), the change in reflectance with respect to the change in the film thickness of the dielectric multilayer film 150 can be made even smaller.

[0123] 3λ / 16 ≤ nj × dj ≤ 5λ / 16 Formula (9)

[0124] Also, from the relationship between the above-mentioned formula (4) and the above-mentioned (5) and the region surrounded by the broken line 450 of the parallelogram indicating the vicinity of the intersection points 440 to 443, the following formula (10) is calculated.

[0125] [Number]

[0126] Note that m3 is a positive integer.

[0127] According to this, even when the nitride semiconductor laser element 10 is driven (when the laser light 201 is emitted to the nitride semiconductor laser element 10), the variation (change) in the reflectance of the dielectric multilayer film 150 can be suppressed. Therefore, the variation in the optical output during the driving of the nitride semiconductor laser element 10 and the deterioration of the nitride semiconductor laser element 10 can be suppressed.

[0128] From the above, by satisfying the above-described first film thickness condition and the above-described second film thickness condition, even when aging occurs, the amount of change in the reflectance of the dielectric multilayer film 150 can be reduced, and the change in the reflectance with respect to the change in the film thickness of the dielectric multilayer film 150 can be reduced. That is, according to the nitride semiconductor laser element 10 including the dielectric multilayer film 150 that satisfies the above-described first film thickness condition and the above-described second film thickness condition, the change in the optical characteristics can be suppressed.

[0129] FIGS. 11A to 11F are graphs showing the amount of change in the reflectance with respect to the film thickness before and after aging of the dielectric multilayer film 150 included in the nitride semiconductor laser element 10 according to the embodiment. Note that the graphs showing the reflectance with respect to the film thickness shown in FIGS. 11A to 11F are the same as those in FIGS. 9A to 9F.

[0130] If it is within the range of the region surrounded by the broken line 450 shown in FIGS. 11A to 11F, the change in the reflectance with respect to the change in the film thickness of the dielectric multilayer film 150 can be reduced.

[0131] Also, if it is within the range of the area surrounded by the rectangular broken line 430 shown in FIGS. 11B to 11D, even when aged, the amount of change in the reflectance of the dielectric multilayer film 150 can be reduced. That is, if it is within the range of the area surrounded by the broken line 430 and within the range of the area surrounded by the broken line 450 shown in FIGS. 11B to 11D, the change in the optical characteristics of the dielectric multilayer film 150 can be more suppressed.

[0132] FIG. 12 is a graph showing the reflectance of the dielectric multilayer film 150 with respect to the wavelength of the nitride semiconductor laser element 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 at the position 461 shown in FIG. 11C, that is, within the range of the area surrounded by the broken line 430 and within the range of the area surrounded by the broken line 450. Further, the graph shown in FIG. 3 shows the reflectance of the dielectric multilayer film that satisfies the film thickness condition at the position 460 shown in FIG. 11B, that is, outside the range of the area surrounded by the broken line 430 and outside the range of the area surrounded by the broken line 450.

[0133] As shown in FIG. 12, it can be seen that the reflectance of the dielectric multilayer film 150 that satisfies the above-described first film thickness condition and the above-described second film thickness condition hardly changes before and after aging, for example, with respect to light having a wavelength of 400 nm.

[0134] [Effects, etc.] As described above, the nitride semiconductor laser device 10 includes a plurality of semiconductor layers including a waveguide 110 (for example, a first semiconductor layer 102, an active layer 103, and a second semiconductor layer 104), and a stacked structure 100 having a pair of resonator end faces (a front side end face 100F and a rear side end face 100R) facing each other, and a dielectric multilayer film 150 disposed on at least one of the pair of resonator end faces (in this embodiment, the front side end face 100F). The dielectric multilayer film 150 has a first dielectric film 120, a second dielectric film 130, and a third dielectric film 140 in this order from the resonator end face side. The first dielectric film 120 is composed of n (n is a positive integer) layers of protective films from the first protective film to the nth protective film in order from the resonator end face 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 124.

[0135] In the nitride semiconductor laser device 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 denoted as nk and dk, respectively, the refractive index and film thickness of the second dielectric film 130 are denoted as ni and di, respectively, the refractive index and film thickness of the third dielectric film 140 are denoted as nj and dj, respectively, m1 is an integer of 2 or more, and m2 is a positive integer, the above-described formula (7) is satisfied, the above-described formula (8) is satisfied, and the above-described formula (6) is satisfied.

[0136] According to this, in the dielectric multilayer film 150 included in the nitride semiconductor laser device 10, by appropriately combining the film thickness and refractive index of each film included in the dielectric multilayer film 150, even if the film thickness of the dielectric multilayer film 150 fluctuates, the fluctuation of the reflectance can be suppressed to be small. Therefore, the fluctuation of the light output during the driving of the nitride semiconductor laser device 10 and the deterioration of the nitride semiconductor laser device 10 can be suppressed. That is, according to the nitride semiconductor laser device 10, the deterioration of the optical characteristics can be suppressed.

[0137] Alternatively, the nitride semiconductor laser element 10 satisfies the above-described formula (7) and also satisfies the above-described formula (8). Further, one of the second dielectric film 130 and the third dielectric film 140 has a property that the film thickness decreases due to the laser light 201 emitted from the nitride semiconductor laser element 10, and the other has a property that the film thickness increases due to the laser light 201 emitted from the nitride semiconductor laser element 10.

[0138] Also, thereby, in the dielectric multilayer film 150 included in the nitride semiconductor laser element 10, even if the film thickness of the dielectric multilayer film 150 fluctuates, by appropriately combining the film thickness and refractive index of each film included in the dielectric multilayer film 150, the fluctuation of the reflectance can be suppressed to be small. Therefore, the fluctuation of the optical output during driving of the nitride semiconductor laser element 10 and the deterioration of the nitride semiconductor laser element 10 can be suppressed.

[0139] Further, for example, in response to the laser light 201 emitted from the resonator end face, a concave portion 131 is formed in the second dielectric film 130 and a convex portion 141 is formed in the third dielectric film 140 at the interface between the second dielectric film 130 and the third dielectric film 140.

[0140] According to this, even when the laser light 201 is irradiated, the change amount of the total film thickness of the dielectric multilayer film 150 can be made small. Therefore, the change in the reflectance of the dielectric multilayer film 150 is further suppressed.

[0141] Further, 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 resonator end face.

[0142] According to this, since the change in the film thickness of the dielectric multilayer film 150 occurs in the optical path of the laser light 201, the change amount of the total film thickness of the dielectric multilayer film 150 in the region through which the laser light 201 passes is reduced. Therefore, the change in the reflectance of the dielectric multilayer film 150 is further suppressed.

[0143] Further, for example, the third dielectric film 140 has an amorphous structure.

[0144] This provides the third dielectric film 140 with a property of absorbing a rare gas such as Ar contained in the second dielectric film 130 and increasing its thickness.

[0145] Moreover, for example, the nitride semiconductor laser device 10 further satisfies the above formula (9).

[0146] 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.

[0147] Moreover, for example, the oscillation wavelength of the nitride semiconductor laser device 10 is 420 nm or less.

[0148] 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 having a wavelength of 420 nm or less, which is a wavelength at which the dielectric multilayer film 150 is likely to absorb laser light 201.

[0149] Moreover, for example, the nitride semiconductor laser device 10 emits laser light 201 of 1 W or more.

[0150] The change in the film thickness of the dielectric multilayer film 150 depends greatly on the optical output of the laser light 201. For example, the change in the film thickness of the dielectric multilayer film 150 is noticeable when the laser light 201 has an optical output of 1 W or more. Therefore, the configuration of the dielectric multilayer film 150 is particularly effective as an end face coating film in a nitride semiconductor laser device 10 that emits laser light 201 of 1 W or more, which is likely to affect the film thickness of the dielectric multilayer film 150.

[0151] Furthermore, for example, the nitride semiconductor laser device 10 satisfies the above formula (10) when m3 is a positive integer.

[0152] 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.

[0153] Also, for example, the second dielectric film 130 is any one of Al2O3, Ta2O5, and ZrO2, and the third dielectric film 140 is any one of SiO2, B2O3, P2O5, and GeO2.

[0154] According to this, in the dielectric multilayer film 150, it is possible to combine a film whose film thickness decreases by absorbing the laser light 201 and a film whose film thickness increases. Therefore, fluctuations in the optical output during driving of the nitride semiconductor laser element 10 and deterioration of the nitride semiconductor laser element 10 can be suppressed.

[0155] Also, for example, an aluminum oxynitride film is disposed between the resonator end face and the dielectric multilayer film 150.

[0156] According to this, oxidation of the resonator end face in the nitride semiconductor laser element 10 can be suppressed by the aluminum oxynitride film. Also, according to this, the dangling bonds in the resonator end face and the dielectric multilayer film 150 can be reduced. Therefore, for example, even when the nitride semiconductor laser element 10 is driven to have a high optical output, deterioration of the dielectric multilayer film 150 can be suppressed.

[0157] Also, for example, the aluminum oxynitride film contains crystalline aluminum nitride. In this case, the aluminum oxynitride film may be polycrystalline aluminum nitride, or may be a film containing a large amount of oxygen at the grain boundaries of polycrystalline aluminum nitride.

[0158] According to this, since the aluminum oxynitride film contains crystals, oxidation of the resonator end face in the nitride semiconductor laser element 10 can be further suppressed. Also, according to this, the dangling bonds in the resonator end face and the dielectric multilayer film 150 can be further reduced. Therefore, for example, even when the nitride semiconductor laser element 10 is driven to have a high optical output, deterioration of the dielectric multilayer film 150 can be further suppressed.

[0159] Further, for example, between the resonator end face and the dielectric multilayer film, there is disposed a film made of at least one of aluminum nitride silicon, aluminum nitride gallium, aluminum nitride yttrium, aluminum nitride lanthanum, aluminum oxynitride silicon, aluminum oxynitride gallium, aluminum oxynitride yttrium, and aluminum oxynitride lanthanum.

[0160] This also enables suppression of oxidation of the resonator end face in the nitride semiconductor laser element 10, similar to the aluminum oxynitride film. Further, according to this, it is possible to reduce dangling bonds in the resonator end face and the dielectric multilayer film 150. Therefore, for example, even when the nitride semiconductor laser element 10 is driven to have a high optical output, deterioration of the dielectric multilayer film 150 can be suppressed.

[0161] (Other Embodiments) As described above, the nitride semiconductor laser element according to the present disclosure has been described based on the above embodiments, but the present disclosure is not limited to the above embodiments. Forms obtained by applying various modifications conceivable by those skilled in the art to the above embodiments, and forms realized by arbitrarily combining the components and functions in the above embodiments without departing from the spirit of the present disclosure are also included in the present disclosure.

Industrial Applicability

[0162] The nitride semiconductor laser element of the present disclosure can be used, for example, as a light source for industrial laser devices such as industrial lighting, facility lighting, in-vehicle headlamps, and laser processing machines, and image display devices such as laser displays and projectors.

Explanation of Reference Numerals

[0163] 10 Nitride semiconductor laser element 100 Stacked structure 100a First conductivity type semiconductor layer 100b Second conductivity type semiconductor layer 100F Front side end face 100R Rear side 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 First electrode 110 Waveguide 120 First dielectric film 121 First protective film 122 Second protective film 123 Third protective film 124 Fourth protective film 130 Second dielectric film 131 Recess 140 Third dielectric film 141 Protrusion 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 point 460, 461 Position

Claims

1. A stacked structure composed of a plurality of semiconductor layers including a waveguide and having a pair of resonator end faces facing each other, and a dielectric multilayer film disposed on the end face on the light emission side of the pair of resonator end faces, a nitride semiconductor laser element comprising: The dielectric multilayer film has a first dielectric film, a second dielectric film, and a third dielectric film in this order from the end face side of the light emission side, The first dielectric film is composed of n (n is a positive integer) layers of protective films from a first protective film to an nth protective film in order from the end face side of the light emission side, Let the refractive index and film thickness of the kth (k is an integer satisfying 1 ≤ k ≤ n) protective film in the first dielectric film be nk and dk, respectively, Let the refractive index and film thickness of the second dielectric film be ni and di, respectively, Let the refractive index and film thickness of the third dielectric film be nj and dj, respectively, Let m1 be an integer of 2 or more, When m2 is a positive integer, 【Number 1】 satisfies, nj × dj = m2 × λ / 4 ± λ / 16 satisfies, and 【Number 2】 satisfies, On the surface of the third dielectric film opposite to the surface where the second dielectric film is located, no dielectric film is provided Nitride semiconductor laser element.

2. A stacked structure composed of a plurality of semiconductor layers including a waveguide and having a pair of resonator end faces facing each other, and a dielectric multilayer film disposed on the end face on the light emission side of the pair of resonator end faces, a nitride semiconductor laser element comprising: The dielectric multilayer film has a first dielectric film, a second dielectric film, and a third dielectric film in this order from the end face side of the light emission side, The first dielectric film is composed of n (n is a positive integer) layers of protective films from a first protective film to an nth protective film in order from the end face side of the light emission side, Let the refractive index and film thickness of the kth (k is an integer satisfying 1 ≤ k ≤ n) protective film in the first dielectric film be nk and dk, respectively, Let the refractive index and film thickness of the second dielectric film be ni and di, respectively, Let the refractive index and film thickness of the third dielectric film be nj and dj, respectively, Let m1 be an integer of 2 or more, When m2 is a positive integer, 【Mathematics 3】 satisfies, nj × dj = m2 × λ / 4 ± λ / 16 satisfies, and [Number 4] satisfies, At the interface between the second dielectric film and the third dielectric film, The second dielectric film has a concave portion, The third dielectric film has a convex portion Nitride semiconductor laser element.

3. A stacked structure composed of a plurality of semiconductor layers including a waveguide and having a pair of resonator end faces facing each other, and A nitride semiconductor laser device comprising a dielectric multilayer film disposed on an end face on the light emitting side of the pair of resonator end faces. The dielectric multilayer film has, in this order from the end face side on the light emitting side, a first dielectric film, a second dielectric film, and a third dielectric film. The first dielectric film is composed of n (n is a positive integer) layers of protective films from a first protective film to an nth protective film in order from the end face side on the light emitting side. Let the refractive index and film thickness of the kth (k is an integer satisfying 1 ≤ k ≤ n) protective film in the first dielectric film be nk and dk, respectively. Let the refractive index and film thickness of the second dielectric film be ni and di, respectively. Let the refractive index and film thickness of the third dielectric film be nj and dj, respectively. Let m1 be an integer of 2 or more. When m2 is a positive integer, 【Number 5】 Satisfying nj × dj = m2 × λ / 4 ± λ / 16 Satisfying, and 【Number 6】 Satisfying Furthermore, 3λ / 16 ≤ nj × dj ≤ 5λ / 16 Satisfying Nitride semiconductor laser device.

4. A nitride semiconductor laser device comprising a laminated structure composed of a plurality of semiconductor layers including a waveguide and having a pair of resonator end faces facing each other, A dielectric multilayer film disposed on an end face on the light emitting side of the pair of resonator end faces. The dielectric multilayer film has, in this order from the end face side on the light emitting side, a first dielectric film, a second dielectric film, and a third dielectric film. The first dielectric film is composed of n (n is an integer of 1 or more) layers of protective films from a first protective film to an nth protective film in order from the end face side on the light emitting side. Let the refractive index and film thickness of the kth (k is an integer satisfying 1 ≤ k ≤ n) protective film in the first dielectric film be nk and dk, respectively. Let the refractive index and film thickness of the second dielectric film be ni and di, respectively. Let the refractive index and film thickness of the third dielectric film be nj and dj, respectively. Let m1 be an integer of 2 or more. When m2 is a positive integer, 【Number 7】 Satisfying, and nj × dj = m2 × λ / 4 ± λ / 16 Satisfying One of the second dielectric film and the third dielectric film has a property that its film thickness decreases due to the laser light emitted from the nitride semiconductor laser device. The other has a property that its film thickness increases due to the laser light emitted from the nitride semiconductor laser device. A dielectric film is not provided on the surface of the third dielectric film opposite to the surface where the second dielectric film is located. Nitride semiconductor laser device.

5. A laminated structure composed of a plurality of semiconductor layers including a waveguide and having a pair of resonator end faces facing each other, A nitride semiconductor laser device comprising a dielectric multilayer film disposed on an end face on the light-emitting side of the pair of resonator end faces. The dielectric multilayer film has, in this order from the end face side on the light-emitting side, a first dielectric film, a second dielectric film, and a third dielectric film. The first dielectric film is composed of n (n is an integer of 1 or more) layers of protective films from a first protective film to an nth protective film in order from the end face side on the light-emitting side. Let the refractive index and film thickness of the kth (k is an integer satisfying 1 ≦ k ≦ n) protective film in the first dielectric film be nk and dk, respectively. Let the refractive index and film thickness of the second dielectric film be ni and di, respectively. Let the refractive index and film thickness of the third dielectric film be nj and dj, respectively. Let m1 be an integer of 2 or more. When m2 is a positive integer. 【Number 8】 Satisfies, and nj × dj = m2 × λ / 4 ± λ / 16 Satisfies, One of the second dielectric film and the third dielectric film has a property that the film thickness decreases due to the laser light emitted from the nitride semiconductor laser device. The other has a property that the film thickness increases due to the laser light emitted from the nitride semiconductor laser device. At the interface between the second dielectric film and the third dielectric film. The second dielectric film has a concave portion. The third dielectric film has a convex portion. Nitride semiconductor laser device. [

6. ] A stacked structure composed of a plurality of semiconductor layers including a waveguide and having a pair of resonator end faces facing each other, A nitride semiconductor laser device comprising a dielectric multilayer film disposed on an end face on the light-emitting side of the pair of resonator end faces. The dielectric multilayer film has, in this order from the end face side on the light-emitting side, a first dielectric film, a second dielectric film, and a third dielectric film. The first dielectric film is composed of n (n is an integer of 1 or more) layers of protective films from a first protective film to an nth protective film in order from the end face side on the light-emitting side. Let the refractive index and film thickness of the kth (k is an integer satisfying 1 ≦ k ≦ n) protective film in the first dielectric film be nk and dk, respectively. Let the refractive index and film thickness of the second dielectric film be ni and di, respectively. Let the refractive index and film thickness of the third dielectric film be nj and dj, respectively. Let m1 be an integer of 2 or more. When m2 is a positive integer. 【Number 9】 Satisfies, and nj × dj = m2 × λ / 4 ± λ / 16 Satisfies, One of the second dielectric film and the third dielectric film has a property that the film thickness decreases due to the laser light emitted from the nitride semiconductor laser device. The other has a property that the film thickness increases due to the laser light emitted from the nitride semiconductor laser element. Furthermore, 3λ / 16 ≤ nj × dj ≤ 5λ / 16 is satisfied nitride semiconductor laser element.

7. At the interface between the second dielectric film and the third dielectric film, the second dielectric film has a concave portion, the third dielectric film has a convex portion The nitride semiconductor laser element according to any one of Claims 1, 3, 4, and 6.

8. The concave portion and the convex portion are located on the optical path of the laser light emitted from the end face on the light emission side The nitride semiconductor laser element according to any one of Claims 2, 5, and 7.

9. The third dielectric film has an amorphous structure The nitride semiconductor laser element according to any one of Claims 1 to 8.

10. Furthermore, 3λ / 16 ≤ nj × dj ≤ 5λ / 16 is satisfied The nitride semiconductor laser element according to any one of Claims 1, 2, 4, 5, and 7 to 9.

11. The oscillation wavelength of the nitride semiconductor laser element is 420 nm or less The nitride semiconductor laser element according to any one of Claims 1 to 10.

12. The nitride semiconductor laser element emits laser light of 1 W or more The nitride semiconductor laser element according to any one of Claims 1 to 11.

13. When m3 is a positive integer, furthermore, 【Number 10】 is satisfied The nitride semiconductor laser element according to any one of Claims 1 to 12.

14. The second dielectric film is Al ２ O ３ Ta ２ O ５ ZrO ２ any one of, and The third dielectric film is SiO ２ , B ２ O ３ , P ２ O ５ , and GeO ２ or any one of them The nitride semiconductor laser element according to any one of Claims 1 to 13.

15. An aluminum oxynitride film is disposed between the end face on the light emission side and the dielectric multilayer film. The nitride semiconductor laser element according to any one of Claims 1 to 14.

16. The aluminum oxynitride film contains crystalline aluminum nitride. The nitride semiconductor laser element according to Claim 15.

17. Between the end face on the light emission side and the dielectric multilayer film, a film composed of at least one of aluminum nitride silicon, aluminum nitride gallium, aluminum nitride yttrium, aluminum nitride lanthanum, aluminum oxynitride silicon, aluminum oxynitride gallium, aluminum oxynitride yttrium, and aluminum oxynitride lanthanum is disposed. The nitride semiconductor laser element according to any one of Claims 1 to 16.

18. Furthermore, 【Number 11】 is satisfied The nitride semiconductor laser element according to any one of Claims 4 to 6.

19. The first dielectric film is in contact with the end face on the light-emitting side The nitride semiconductor laser device according to any one of claims 1 to 14 and 18.

20. n is a positive integer of 2 or more The nitride semiconductor laser device according to any one of claims 1 to 19.

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