JP2020031239A - Semiconductor laser element and manufacturing method of the same - Google Patents

Abstract

To provide a semiconductor laser element and a manufacturing method of the same, which can reduce variation in threshold current.SOLUTION: In a semiconductor laser element manufacturing method comprising the steps of: preparing a nitride semiconductor structure having a light emission side face and a light reflection side face to obtain a wavelength λo as an oscillation wavelength target value; forming an emission side mirror on the light emission side face; and forming a reflection side mirror on the light reflection side face, an actual oscillation wavelength λa of the semiconductor laser element is equal to or greater than 500 nm and included within a range of λo±X nm(5≤X≤15); and in the step of forming the emission side mirror, within a range of λo±X nm, the emission side mirror which has reflectivity lower than that of the reflection side mirror and in which the reflectivity increases with increased wavelength is formed on the light emission side face.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a semiconductor laser device and a method for manufacturing the same.

  The semiconductor laser device has a semiconductor structure including an active layer, an emission side mirror provided on a light emission side surface, and a reflection side mirror provided on a light reflection side surface. The reflection-side mirror is a film having a high reflectance of, for example, 80% or more, and the emission-side mirror is a film having a lower reflectance. For example, Patent Literature 1 describes a semiconductor laser device having an emission side mirror having a reflectance of 3 to 13% and having an oscillation wavelength of around 410 nm.

JP 2009-176812 A

  FIG. 3 of Patent Document 1 describes the wavelength dependence of the reflectance of the emission-side mirror. According to this figure, even if the actual oscillation wavelength slightly deviates from the target value, the reflectance of the emission side mirror hardly changes. If the luminous efficiency of the semiconductor structure does not change due to the deviation of the oscillation wavelength, it should be possible to obtain the target threshold current and light output even if the actual oscillation wavelength slightly deviates.

  However, for example, in a semiconductor laser device that oscillates light in a green region of 500 nm or more, the luminous efficiency of the semiconductor structure is still insufficient compared with a semiconductor laser device that oscillates light in a violet to blue region. In such a semiconductor laser device, the emission efficiency of the semiconductor structure tends to decrease as the oscillation wavelength becomes longer. Further, for example, a semiconductor laser device having an emission wavelength in a green region has an InGaN layer or the like as an active layer. Oscillation wavelength tends to deviate from the target value.

This application includes the following inventions.
A step of preparing a nitride semiconductor structure having a light emitting side surface and a light reflecting side surface with a wavelength λo as a target value of the oscillation wavelength,
Forming an emission side mirror on the light emission side surface;
Forming a reflection-side mirror on the light-reflecting side surface, comprising:
The actual oscillation wavelength λa of the semiconductor laser device is not less than 500 nm and is in the range of λo ± Xnm (5 ≦ X ≦ 15),
In the emission side mirror forming step, within the range of λo ± Xnm, an emission side mirror whose reflectance is lower than that of the reflection side mirror and whose reflectance increases with an increase in wavelength is formed on the light emission side surface. A method for manufacturing a semiconductor laser device.

A nitride semiconductor structure having a light emitting side surface and a light reflecting side surface,
An emission mirror provided on the light emission side surface,
A semiconductor laser device having an oscillation wavelength of 500 nm or more, comprising: a reflection side mirror provided on the light reflection side surface;
The semiconductor laser, wherein the emission side mirror has a reflectance lower than the reflectance of the reflection side mirror and increases with an increase in wavelength in a wavelength region including the oscillation wavelength and having a width of 10 nm or more and 30 nm or less. element.

  According to the invention, it is possible to provide a semiconductor laser device capable of reducing variation in threshold current and a method of manufacturing the same.

4 is a flowchart schematically illustrating a manufacturing process according to the embodiment. FIG. 5 is a schematic cross-sectional view for explaining a manufacturing process of the semiconductor laser device according to the embodiment. FIG. 5 is a schematic cross-sectional view for explaining a manufacturing process of the semiconductor laser device according to the embodiment. FIG. 3 is a partially enlarged view showing an emission side mirror and its vicinity. 6 is a graph showing the wavelength dependence of the reflectance of the exit side mirror of the example. 9 is a graph showing the wavelength dependence of the reflectance of the exit-side mirror of Comparative Example 1. 9 is a graph showing the wavelength dependence of the reflectance of the exit-side mirror of Comparative Example 2. FIG. 1 is a schematic cross-sectional view illustrating a semiconductor laser device according to an embodiment. 4 is a graph showing a relationship between an oscillation wavelength and a threshold current of the semiconductor laser device of the example. 4 is a graph showing the relationship between the current and the optical output of the semiconductor laser devices having an oscillation wavelength of 520 nm of the example and comparative examples 1 and 2. 5 is a graph showing the relationship between the current and the optical output of the semiconductor laser device having an oscillation wavelength of 525 nm in the example and comparative examples 1 and 2.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the embodiments described below exemplify a method for embodying the technical idea of the present invention, and do not limit the present invention to the following embodiments. Further, in the following description, the same names and reference numerals denote the same or similar members, and a detailed description thereof will be omitted as appropriate.

As shown in FIG. 1, the method for manufacturing a semiconductor laser device according to the present embodiment includes the following steps.
S100: a step of preparing a nitride semiconductor structure having a light emitting side surface and a light reflecting side surface with a wavelength λo as a target value of the oscillation wavelength.
S202: Step of forming an emission side mirror on the light emission side surface.
S204: forming a reflection side mirror on the light reflection side surface.
Here, the actual oscillation wavelength λa of the semiconductor laser element is not less than 500 nm and is in the range of λo ± Xnm (5 ≦ X ≦ 15). In the step of forming the emission-side mirror, an emission-side mirror whose reflectance is lower than that of the reflection-side mirror and whose reflectance increases with an increase in wavelength within the range of λo ± Xnm is formed on the light emission side surface.

(Step S100 of Preparing Nitride Semiconductor Structure)
First, as shown in FIG. 2, a nitride semiconductor structure 10 having a light emitting side surface 10a and a light reflecting side surface 10b is prepared. As shown in FIG. 1, the step S100 of preparing a nitride semiconductor structure includes, for example, a substrate preparing step, S102, an n-side semiconductor layer forming step S104, an active layer forming step S106, and a p-side semiconductor layer forming step. S108. That is, as shown in FIG. 2, the nitride semiconductor structure 10 can include the n-side semiconductor layer 11, the active layer 12, and the p-side semiconductor layer 13 in this order upward. Each of the n-side semiconductor layer 11, the active layer 12, and the p-side semiconductor layer 13 is made of a nitride semiconductor. The nitride semiconductor structure 10 can be formed on the substrate 20. FIG. 2 is a diagram showing a cross section in a direction parallel to the resonator direction, that is, a direction parallel to the extension direction of a ridge 13a described later.

  The nitride semiconductor structure 10 is designed so that the oscillation wavelength of a semiconductor laser device formed using the nitride semiconductor structure 10 is a specific wavelength. Here, the target specific wavelength is defined as wavelength λo. For example, as the target of the composition of the well layer in the active layer 12 when the wavelength λo is 520 nm, InGaN having an In composition ratio of 25% can be mentioned. If the nitride semiconductor structure 10 having the desired composition or the like is obtained, the oscillation wavelength of the semiconductor laser device formed using the same should be the target value λo. However, the composition and the like of the nitride semiconductor structure 10 actually obtained do not always completely match the target values, and in many cases, the composition and the like slightly different from the target compositions and the like are obtained. Similarly, the actual oscillation wavelength λa may be slightly different from the target wavelength λo. If the difference between the actual oscillation wavelength λa and the wavelength λo is relatively small, it can be accepted as a good product. Therefore, the actual oscillation wavelength λa is set within the range of λo ± Xnm (5 ≦ X ≦ 15). In this embodiment, X = 15. The semiconductor laser device obtained by using the nitride semiconductor structure 10 is a laser device that oscillates green laser light, and the actual oscillation wavelength λa is 500 nm or more. Further, the oscillation wavelength λa can be in the range of 515 to 540 nm. Note that the oscillation wavelength indicates a peak wavelength.

As the substrate 20, a substrate made of a semiconductor such as GaN or a substrate made of an insulating material such as sapphire can be used. For example, a GaN substrate whose upper surface is c-plane ((0001) plane) is used as the substrate 20. The n-side semiconductor layer 11 can have a multilayer structure made of a nitride semiconductor such as GaN, InGaN, or AlGaN. Examples of the n-type semiconductor layer included in the n-side semiconductor layer 11 include a layer made of a nitride semiconductor containing an n-type impurity such as Si or Ge. The active layer 12 may have a single quantum well structure or a multiple quantum well structure.
The active layer 12 has, for example, an InGaN well layer and a GaN barrier layer. The p-side semiconductor layer 13 can have a multilayer structure including a nitride semiconductor layer such as GaN, InGaN, or AlGaN. Examples of the p-type nitride semiconductor layer included in the p-side semiconductor layer 13 include a layer made of a nitride semiconductor containing a p-type impurity such as Mg.

  As shown in FIG. 2, an n-electrode 30 can be provided on the lower surface of the substrate 20. Further, a p-electrode 41 can be provided in contact with the upper surface of the p-side semiconductor layer 13, and a p-side pad electrode 42 can be further provided thereon. The material of each electrode is, for example, a single metal such as a metal or alloy such as Ni, Rh, Cr, Au, W, Pt, Ti, and Al, or a conductive oxide containing at least one selected from Zn, In, and Sn. A layer film or a multilayer film is used. Examples of the conductive oxide include ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), and GZO (Gallium-doped Zinc Oxide).

  For example, using a wafer-shaped substrate 20, an n-side semiconductor layer 11, an active layer 12, and a p-side semiconductor layer 13 are sequentially formed thereon, and a cleavage plane obtained by cutting the n-side semiconductor layer 11, the active layer 12, and the p-side semiconductor layer 13 is emitted. The side surface 10a and the light reflection side surface 10b can be used.

(Step S202 of Forming Output Side Mirror)
After preparing the nitride semiconductor structure 10, as shown in FIG. 3A, an emission side mirror 50 is formed on the light emission side surface 10a. The emission side mirror 50 has a lower reflectance than the later-described reflection side mirror 60 within the range of λo ± Xnm, and the reflectance increases as the wavelength increases. FIG. 4 is a graph showing an example of the wavelength dependence of the reflectance of the emission side mirror 50.

  As described above, in a semiconductor laser device having an oscillation wavelength in the green region, the emission efficiency of the nitride semiconductor structure 10 tends to decrease as the oscillation wavelength becomes longer. Therefore, an emission-side mirror 50 having a wavelength-dependent reflectance as shown in FIG. 4 is formed. For example, if the actual oscillation wavelength λa is longer than the wavelength λo, the luminous efficiency of the nitride semiconductor structure 10 is reduced and the reflectance is lower than when the actual oscillation wavelength λa has the same value as the wavelength λo. To rise.

Threshold current _{I th} of the semiconductor laser device is directly proportional to the threshold current density _{J th.} Then, the threshold current density J _th is increased as the luminous efficiency of the nitride semiconductor structure 10, that is, the internal quantum efficiency eta _i decreases, The reflectance of the output mirror 50 is reduced enough to rise. That is, the actual oscillation wavelength λa is lowered luminous efficiency by being a long wave than the wavelength .lamda.o, should the threshold current I _th would otherwise increase. However, on the other hand, the reflectance of the output mirror 50 is increased, it is possible to actual oscillation wavelength λa is even to reduce the deviation from the target value of the threshold current I _th as deviated from the wavelength .lamda.o. Thereby, the yield of the semiconductor laser device can be improved. Further, as the variation in the threshold current is reduced, there is an advantage that the laser oscillation on current and / or off current can be set more strictly when incorporated in an application.

Smaller degree of change with increasing wavelength of the reflectivity of the output mirror 50, the effect is difficult to obtain to reduce the deviation from the target value of the threshold current I _th. For this reason, it is preferable that the output side mirror 50 has a reflectance that changes by 2% or more every time the wavelength increases by 10 nm within the range of λo ± Xnm. On the other hand, if the degree of change in the reflectance is too large, it is considered that stable characteristics cannot be easily obtained. Therefore, the change in the reflectance every 10 nm is preferably 10% or less. In addition, since the luminous efficiency of the nitride semiconductor structure 10 tends to change substantially linearly within the range of λo ± Xnm, it is preferable that the reflectance of the emission side mirror 50 also changes substantially linearly. For example, in the graph of the wavelength dependence of the reflectance of the emission side mirror 50 shown in FIG. 4, it can be said that there is substantially no inflection point within the range of λo ± Xnm.

  It is preferable that the reflectance of the emission side mirror 50 increases in accordance with the wavelength increase in the wavelength range before and after λo ± Xnm in addition to the range of λo ± Xnm. Such a wavelength range includes a range of λo ± (X + 5) nm. In other words, in the graph of the wavelength dependence of the reflectance of the emission-side mirror 50, the inflection point is preferably outside the range of λo ± (X + 5) nm. When the film thickness or the refractive index of the emission side mirror 50 deviates from the target value, the reflectivity changes from the target value. However, by providing a margin in the wavelength range in this way, even if the film thickness and the like slightly deviate, it is stabilized. Properties can be obtained.

As shown in FIG. 3B, the emission-side mirror 50 can have a laminated structure in which two or more types of films having different refractive indexes are laminated. The output side mirror 50 is, for example, sequentially from the light output side surface 10a.
An Al ₂ O ₃ film 51a having a thickness of 158 nm,
A ZrO ₂ film 52 having a thickness of 59 nm,
An Al ₂ O ₃ film 51 b having a thickness of 79 nm,
A ZrO ₂ film 52 having a thickness of 59 nm,
An Al ₂ O ₃ film 51 b having a thickness of 79 nm,
A ZrO ₂ film 52 having a thickness of 59 nm,
A 180 nm thick Al ₂ O ₃ film 53,
Are formed by stacking. In this embodiment, the target wavelength λo is 520 nm, so that a total of six layers from the Al ₂ O ₃ film 51a to the ZrO ₂ film 52 in contact with the light emitting side surface 10a are substantially integer multiples of λo / 4n. It is a thick λ / 4 film. The outermost film Al ₂ O ₃ film 53 is a non-λ / 4 film having a thickness substantially different from an integral multiple of λo / 4n. Note that n indicates the refractive index of each film. Further, these values are target values, and the actual film thickness may be slightly deviated therefrom. For example, the actual thickness of each film may deviate from the target value by about 0 to 10 nm.

In such an emission side mirror 50, if the outermost Al ₂ O ₃ film 53 has a thickness of 158 nm, it becomes a λ / 4 film. In this case, as shown in FIG. 5, the reflectance is substantially unchanged at the wavelength λo and before and after the wavelength λo. From this, it is possible to obtain a reflectance that changes with an increase in wavelength by forming the emission side mirror 50 to have a structure having at least one λ / 4 film and at least one non-λ / 4 film. It is considered possible. It should be noted that even if the film thickness of the Al ₂ O ₃ film 53 is further reduced to a film thickness of 130 nm, the film becomes a non-λ / 4 film. In this case, as shown in FIG. Reduces the reflectance. From these facts, by making a part of the emission side mirror 50 a non-λ / 4 film and adjusting the thickness of the non-λ / 4 film, as shown in FIG. It is believed that the reflectivity can vary.

  As shown in FIG. 6, if the reflectance decreases as the wavelength increases, the threshold current decreases if the oscillation wavelength is in a short wavelength region where the reflectance is relatively high, and the long wavelength has a relatively low reflectance. In the range, the threshold current increases. For this reason, the variation in the threshold current tends to be larger than in the case of using the emission side mirror 50 of the present embodiment. In addition, as shown in FIG. 6, that the reflectance decreases as the oscillation wavelength becomes longer, that is, the light confinement decreases as the oscillation wavelength becomes longer. Although the light output is lower in a high-temperature atmosphere than in a room-temperature atmosphere, the degree of this decrease is considered to be smaller when the light confinement is higher, especially in a long wavelength region. For this reason, in the long wavelength region of, for example, 525 nm or more, the emission side mirror 50 has a structure in which the long wave has a higher reflectance as shown in FIG. 4 than a structure in which the longer wave has a lower reflectance as shown in FIG. preferable.

  In addition, it is considered that as the number of non-λ / 4 films increases, the wavelength dependency and the angle dependency tend to have many change points. For this reason, it is preferable that the number of non-λ / 4 films is small, that is, that there are a plurality of λ / 4 films, and that the number is larger than the number of non-λ / 4 films. More preferably, the number of non-λ / 4 films is one. Also, when the thickness of the film disposed relatively close to the nitride semiconductor structure 10 is changed, the electric field strength at the interface between the nitride semiconductor structure 10 and the emission side mirror 50 tends to change. The larger the electric field strength at the interface, the more easily the interface and its vicinity are damaged. As shown in FIG. 3B, it is preferable to use a non-λ / 4 film as the outermost film because it hardly affects the electric field strength at the interface between the nitride semiconductor structure 10 and the emission side mirror 50.

  The emission side mirror 50 is formed at a position on the light emission side surface 10 a that covers at least the active layer 12. The exit side mirror 50 is formed, for example, so as to cover the entire surface of the light exit side surface 10a, and a part of the exit side mirror 50 goes around and / or below the nitride semiconductor structure 10 as shown in FIG. 3A. Is also good. In this case, the film thickness of the wraparound portion may be different from the above film thickness. The nitride semiconductor structure 10 in the emission-side mirror forming step S202 may have a bar shape in which a plurality of portions serving as semiconductor laser elements are connected in a direction parallel to the light emission side surface 10a. Such a bar-shaped nitride semiconductor structure 10 can be obtained by dividing a wafer.

(Step S204 of Forming Reflection Side Mirror)
After preparing the nitride semiconductor structure 10, as shown in FIG. 3A, a reflection-side mirror 60 is formed on the light reflection side surface. The reflection-side mirror forming step S204 may be performed before or simultaneously with the emission-side mirror forming step S202. Within the range of λo ± Xnm, the reflectance of the reflection side mirror 60 is higher than the reflectance of the emission side mirror 50. Thereby, at the time of laser oscillation, the light output of the laser light emitted from the emission side mirror 50 can be made higher than the light output of the laser light emitted from the reflection side mirror 60.

  Since the threshold current can be reduced as the reflectivity of the reflective mirror 60 increases, the reflectivity of the reflective mirror 60 within a range of λo ± Xnm is preferably 90% or more. It is preferable that the reflection-side mirror 60 has a reflectance in which a change amount with respect to an increase in the wavelength within the range of λo ± Xnm is smaller than that of the emission-side mirror. This makes it possible to obtain the same high reflectance anywhere in the range of the actual wavelength λa within the range of λo ± Xnm, so that the variation in the threshold current can be reduced. More preferably, the reflection side mirror 60 has a substantially constant reflectance within the range of λo ± Xnm.

The reflection-side mirror 60 can have a laminated structure in which two or more types of films having different refractive indexes are laminated. The reflection side mirror 60 is, for example, sequentially from the light reflection side surface 10b.
An Al ₂ O ₃ film having a thickness of 158 nm,
A 61 nm thick Ta ₂ O ₅ film,
6 pairs of 87 nm thick SiO ₂ film and 61 nm thick Ta ₂ O ₅ film
It is formed by stacking a 174 nm thick SiO ₂ film. Since the target wavelength λo in the present embodiment is 520 nm, each film constituting the reflection-side mirror 60 is a λ / 4 film having a thickness substantially an integral multiple of λo / 4n. Note that n indicates the refractive index of each film. Further, these values are target values, and the actual film thickness may be slightly deviated therefrom. For example, the actual thickness of each film may deviate from the target value by about 0 to 10 nm.

  Like the emission side mirror 50, the reflection side mirror 60 is formed at a position on the light reflection side surface 10b that covers at least the active layer 12, and is formed, for example, so as to cover the entire surface. As shown in FIG. 3A, a part of the reflection-side mirror 60 may wrap around the nitride semiconductor structure 10 above and / or below, and the film thickness of the wrapped part is different from the above-described film thickness. May be. The nitride semiconductor structure 10 in the reflection-side mirror forming step S204 may have a bar shape in which a plurality of portions serving as semiconductor laser elements are connected in a direction parallel to the light reflection side surface 10b.

(Other processes)
In the case where the emission side mirror 50 and the reflection side mirror 60 are formed on a bar-shaped structure in which a plurality of portions serving as the semiconductor laser elements 100 are connected, after these formations are completed, the bar-shaped structure is replaced with a plurality of semiconductor lasers. The method may further include a step of dividing the device 100. Further, the method may further include a step of measuring the actual oscillation wavelength λa and determining a wavelength within the range of λo ± Xnm as a non-defective product.

(Semiconductor laser device 100)
FIG. 7 shows the semiconductor laser device 100 obtained by the above steps. FIG. 7 is a diagram showing a cross section in a direction perpendicular to the resonator direction, that is, a direction perpendicular to the extending direction of the ridge 13a. The actual oscillation wavelength λa of the semiconductor laser device 100 is 500 nm or more. As shown in FIG. 7, the semiconductor laser device 100 includes a nitride semiconductor structure 10 having a light emitting side surface 10a and a light reflecting side surface 10b, an emitting side mirror 50 provided on the light emitting side surface 10a, and a light reflecting side surface 10b. And the reflection-side mirror 60 provided at the first position. The emission side mirror 50 has a reflectance lower than the reflectance of the reflection side mirror 60 and increases as the wavelength increases in a wavelength region having a width of 10 nm or more and 30 nm or less including the actual oscillation wavelength λa. The exit side mirror 50 can have a λ / 4 film and a non-λ / 4 film as described above. At this time, the λ / 4 film and the non-λ / 4 film may be defined based on the actual oscillation wavelength λa of the semiconductor laser device 100. That is, when a wavelength within a wavelength range of 10 nm or more and 30 nm or less including the actual oscillation wavelength λa is λ, a λ / 4 film having a thickness substantially an integral multiple of λ / 4n, substantially λ It can be said that the non-λ / 4 film has a thickness different from an integral multiple of / 4n.

  As described above, in consideration of the possibility that the oscillation wavelength deviates from the target value, the emission side mirror 50 whose reflectance increases when the luminous efficiency of the nitride semiconductor structure 10 decreases reduces the threshold current from the target value. Deviation can be reduced. It is considered that such a configuration is more effective for the semiconductor laser device 100 having an oscillation wavelength in the range of 515 to 540 nm, because the decrease in luminous efficiency becomes more significant as the wavelength becomes longer.

As shown in FIG. 7, for example, a ridge 13a is provided above the p-side semiconductor layer 13. The portion of the active layer 12 immediately below the ridge 13a and its vicinity is an optical waveguide region. Further, an insulating film 70 may be provided on the upper surface of the p-side semiconductor layer 14 continuous from the side surface of the ridge 13a.
The insulating film 70 can be formed of, for example, a single layer or a laminated film of an oxide or a nitride of Si, Al, Zr, Ti, Nb, Ta, or the like. The ridge 13a is formed before the emission side mirror forming step S202 and the reflection side mirror forming step S204. That is, in the nitride semiconductor structure preparing step S100, the nitride semiconductor structure 10 on which the ridge 13a is formed is prepared. Similarly, the insulating film 70 can be formed before the emission-side mirror formation step S202 and the reflection-side mirror formation step S204.

(Example)
As an example, a semiconductor laser device 100 was manufactured as follows.

  First, a GaN substrate having a c-plane as a growth surface was used as a substrate 20, and an n-side semiconductor layer 11, an active layer 12, and a p-side semiconductor layer 13 made of a GaN-based semiconductor were formed thereon. The composition, thickness, and the like of these semiconductor layers were set as the set values such that the oscillation wavelength of the obtained semiconductor laser device 100 became 520 nm. That is, the wavelength λo, which is the target value of the oscillation wavelength, was set to 520 nm. A part of the p-side semiconductor layer 13 was removed to form a ridge 13a. Further, an insulating film 70 covering the upper surface of the p-side semiconductor layer 14 on both sides of the ridge 13a, a p-electrode 41 in contact with the upper surface of the ridge 13a, a p-side pad electrode 42 in contact with the p-electrode 41, and a lower surface of the substrate 20 And the n-electrode 30 contacting with.

The wafer thus obtained was divided into a plurality of bar-shaped pieces. Each small piece had a size having a plurality of ridges 13a. Then, the divided surfaces facing each small piece were defined as a light emitting side surface 10a and a light reflecting side surface 10b, respectively, and the emitting side mirror 50 was formed on the light emitting side surface 10a, and the reflecting side mirror 60 was formed on the light reflecting side surface 10b. Output mirror 50 includes, in order from the light exit surface 10a, the thickness 79 nm _Al 2 _{O 3} film 51a, ZrO ₂ film 52 having a thickness of 59 nm, a film thickness of 79 nm _Al 2 _{O 3} film 51b, ZrO film thickness 59 nm ₂ A film 52, an Al ₂ O ₃ film 51b with a thickness of 79 nm, a ZrO ₂ film 52 with a thickness of 59 nm, and an Al ₂ O ₃ film 53 with a thickness of 180 nm were used.
That is, in the embodiment, the final film of the emission side mirror 50 is a film thicker than the 4 / λ film. These film thicknesses indicate set values. FIG. 4 shows the wavelength dependence of the reflectance of the emission side mirror 50 calculated using these set values. The reflection-side mirror 60, in order from the light-reflecting side surface 10b, _Al 2 _{O 3} film having a thickness of 158 nm, a film thickness of 61 nm _Ta 2 O ₅ film, a SiO ₂ film and the thickness 61 nm of film thickness 87 nm _Ta 2 O Six pairs of _five films were formed as 174 nm thick SiO ₂ films. The reflectance of the reflection-side mirror 60 calculated using these set values was about 97% in the wavelength range of 500 to 550 nm.

  The semiconductor laser device 100 having one ridge 13a was obtained by dividing the small piece provided with the emission side mirror 50 and the reflection side mirror 60 into one ridge 13a. For about 1560 semiconductor laser devices 100 obtained from one wafer, the oscillation wavelength and the threshold current were measured, respectively. For the obtained threshold current value, first, the average value of the threshold current at the oscillation wavelength of 520 nm ± 1 nm was calculated, and the threshold current was normalized using the average value. That is, each threshold current value was divided by the average value. FIG. 8 shows the result. FIG. 8 is a graph in which a normalized threshold current is plotted and an approximate curve is shown. In FIG. 8, each numerical value of the example is indicated by a circle, and the approximate curve is indicated by a solid line. The oscillation wavelength was distributed in the range of 513 to 525 nm.

(Comparative Example 1)
As Comparative Example 1, a semiconductor laser device was manufactured in the same manner as in Example except that the set value of the thickness of the Al ₂ O ₃ film 53 as the final film of the emission-side mirror 50 was changed to 158 nm. That is, in Comparative Example 1, the final film of the emission side mirror 50 was a λ / 4 film. FIG. 5 shows the wavelength dependence of the reflectance of the emission-side mirror 50 calculated using the set values. The oscillation wavelength and the threshold current of each of about 1870 semiconductor laser devices of Comparative Example 1 obtained from one wafer were measured. FIG. 8 shows the result of normalizing the threshold current using the average value of the threshold current at the oscillation wavelength of 520 nm ± 1 nm for the obtained threshold current. 8, each numerical value of Comparative Example 1 is indicated by X, and the approximate curve is indicated by a broken line. The oscillation wavelength was distributed in the range of 513 to 527 nm.

(Comparative Example 2)
As Comparative Example 2, a semiconductor laser device was manufactured in the same manner as in Example except that the set value of the thickness of the Al ₂ O ₃ film 53 as the final film of the emission-side mirror 50 was changed to 130 nm. That is, in Comparative Example 2, the final film of the emission side mirror 50 was a film thinner than the λ / 4 film. FIG. 6 shows the wavelength dependence of the reflectance of the emission-side mirror 50 calculated using the set values. The oscillation wavelength and the threshold current of about 1750 semiconductor laser devices of Comparative Example 2 obtained from one wafer were measured. FIG. 8 shows the result of normalizing the threshold current using the average value of the threshold current at the oscillation wavelength of 520 nm ± 1 nm for the obtained threshold current. In FIG. 8, each numerical value of Comparative Example 2 is indicated by a triangle, and the approximate curve is indicated by a dashed line having a wider interval than that of Example 1.
The oscillation wavelength was distributed in the range of 513 to 525 nm.

  As shown in FIG. 8, the variation in the threshold current of the semiconductor laser device 100 of the example was smaller than the variation of the threshold current of the semiconductor laser devices of Comparative Example 1 and Comparative Example 2. The three equations in FIG. 8 are equations of approximate curves of 1: Example, 2: Comparative Example 1, 3: Comparative Example 2, respectively.

Further, a semiconductor laser device having an oscillation wavelength of 520 nm and a semiconductor laser device having an oscillation wavelength of 525 nm were selected from the examples and comparative examples 1 and 2, and the optical output was measured while changing the current.
The measurement was performed when the case temperature _Tc was 25 ° C. and 85 ° C., respectively. The results are shown in FIGS. FIG. 9 shows the result at the oscillation wavelength of 520 nm, and FIG. 10 shows the result at the oscillation wavelength of 525 nm. 9 and 10, the example is indicated by a solid line, the comparative example 1 is indicated by a broken line, and the comparative example 2 is indicated by a broken line wider than the comparative example 1. As shown in FIGS. 9 and 10, the structure of Comparative Example 2 can obtain an optical output equal to or higher than the other when the oscillation wavelength is 520 nm, but is higher than the other when the oscillation wavelength is 525 nm. Low light output. In particular, the difference was remarkable at 85 ° C. As shown in FIG. 8, in Comparative Example 2, the wavelength dependence of the threshold current tends to be stronger than the others, that is, the rate of increase of the threshold current due to longer wavelength tends to be higher than the others. As described above, in a semiconductor laser device having an oscillation wavelength of, for example, 525 nm or longer, it is considered that the light output is reduced due to the high threshold current. Therefore, it can be said that the example can reduce the degree of reduction of the light output in the high-temperature atmosphere more than the comparative example 2.

REFERENCE SIGNS LIST 100 semiconductor laser element 10 nitride semiconductor structure 10 a light emitting side surface 10 b light reflecting side surface 11 n-side semiconductor layer 12 active layer 13 p-side semiconductor layer 13 a ridge 20 substrate 30 n-electrode 41 p-electrode 42 p-side pad electrode 50 emission-side mirror 51a, 51b Al ₂ O ₃ film (λ / 4 film)
52 ZrO ₂ film (λ / 4 film)
53 Al ₂ O ₃ film (non-λ / 4 film)
60 Reflective mirror 70 Insulating film

Claims (17)

A step of preparing a nitride semiconductor structure having a light emitting side surface and a light reflecting side surface with a wavelength λo as a target value of the oscillation wavelength,
Forming an emission side mirror on the light emission side surface;
Forming a reflection-side mirror on the light-reflecting side surface, comprising:
The actual oscillation wavelength λa of the semiconductor laser device is not less than 500 nm and is in the range of λo ± Xnm (5 ≦ X ≦ 15),
In the emission side mirror forming step, within the range of λo ± Xnm, an emission side mirror whose reflectance is lower than that of the reflection side mirror and whose reflectance increases with an increase in wavelength is formed on the light emission side surface. A method for manufacturing a semiconductor laser device. In the emission side mirror forming step,
It has a laminated structure in which two or more types of films having different refractive indices are laminated,
A plurality of λ / 4 films each having a thickness substantially equal to an integral multiple of λo / 4n,
2. The method according to claim 1, wherein the emission side mirror includes at least one non-λ / 4 film having a thickness substantially different from an integral multiple of λo / 4n. .
(However, n is the refractive index of each film.) In the emission side mirror forming step,
3. The method according to claim 2, wherein the emitting mirror is formed such that the number of the λ / 4 films is larger than the number of the non-λ / 4 films. In the emission side mirror forming step,
4. The method according to claim 3, wherein the outgoing mirror having one non-λ / 4 film is formed. 5. In the emission side mirror forming step,
5. The method according to claim 4, wherein the non-λ / 4 film is the outermost film and forms the emission side mirror. In the emission side mirror forming step,
The semiconductor laser according to any one of claims 1 to 5, wherein the emission-side mirror has a reflectance that changes by 2% or more every time the wavelength increases by 10 nm within the range of λo ± Xnm. Device manufacturing method. In the reflection side mirror forming step,
The reflective mirror according to any one of claims 1 to 6, wherein the reflective mirror has a reflectivity smaller than that of the output mirror in a variation amount with respect to an increase in wavelength within a range of λo ± Xnm. A method for manufacturing a semiconductor laser device. In the reflection side mirror forming step,
8. The method according to claim 7, wherein the reflection side mirror having a substantially constant reflectance within a range of λo ± Xnm is formed.   9. The method for manufacturing a semiconductor laser device according to claim 1, wherein X is 15.   The method of manufacturing a semiconductor laser device according to claim 1, wherein the actual oscillation wavelength λa is in a range of 515 to 540 nm. A nitride semiconductor structure having a light emitting side surface and a light reflecting side surface,
An emission mirror provided on the light emission side surface,
A semiconductor laser device having an oscillation wavelength of 500 nm or more, comprising: a reflection side mirror provided on the light reflection side surface;
The semiconductor laser, wherein the emission side mirror has a reflectance lower than the reflectance of the reflection side mirror and increases with an increase in wavelength in a wavelength region including the oscillation wavelength and having a width of 10 nm or more and 30 nm or less. element. The output side mirror,
A laminated structure in which two or more films having different refractive indices are laminated,
Having at least one λ / 4 film, which is substantially an integral multiple of λ / 4n,
12. The semiconductor laser device according to claim 11, comprising at least one non-λ / 4 film having a thickness substantially different from an integral multiple of λ / 4n.
(However, λ is a wavelength within the above-mentioned wavelength range, and n is a refractive index of each film.)   13. The semiconductor laser device according to claim 12, wherein the number of the non-λ / 4 films is one.   14. The semiconductor laser device according to claim 13, wherein the non-λ / 4 film is an outermost film among films constituting the emission side mirror.   15. The semiconductor laser device according to claim 11, wherein the emission side mirror has a reflectance that changes by 2% or more every time the wavelength increases by 10 nm in the wavelength region.   The semiconductor laser device according to any one of claims 11 to 15, wherein the reflection side mirror has a substantially constant reflectance in the wavelength region.   17. The semiconductor laser device according to claim 11, wherein the oscillation wavelength is in a range of 515 to 540 nm.

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