JP4502867B2 - Semiconductor laser device and manufacturing method of semiconductor laser device - Google Patents

Description

  The present invention relates to a semiconductor laser used as a light source for an optical disc system, information processing or optical communication, and in particular, a semiconductor laser device having an element structure necessary for achieving high-output and highly reliable operation performance and The present invention relates to a method for manufacturing a semiconductor laser device.

  A 650 nm band visible light laser used as a light source for a rewritable high-density optical disk device such as a DVD-RAM requires a high output operation of 50 mW or more, and further higher output is required to support high-speed writing. Has been. As the optical output increases, optical damage due to light absorption at the laser end face portion (Cathotropic Optical Damage: COD) becomes a problem. At present, a method is effective in which Zn is solid-phase diffused in the end face and an end face window structure transparent to the emission wavelength is formed by average composition of an active layer having a multiple quantum well structure.

  The end face window structure is generally manufactured by depositing a ZnO film on the end face portion and annealing to average composition of the multiple quantum well active layer. However, the problem with this method is that when the p-type second cladding layer is etched and the etching is stopped with the p-type GaInP etching stop layer, the resistance to the etching stop layer due to the decrease in crystallinity caused by Zn diffusion is higher than that of the gain portion. It is a significant drop. As a result, when etching beyond the etching stop layer occurs, it adversely affects the optical characteristics including the horizontal divergence angle. On the other hand, in order to increase the output exceeding 200 mW in recent years, the window structure is required to have a large band gap difference and high transparency with respect to the gain portion. It is important to satisfy both of the requirements for ensuring stop layer resistance.

The following measures are taken for the average composition of the active layer.
Hereinafter, a conventional semiconductor laser and a method for manufacturing the semiconductor laser will be described with reference to FIGS.

  6 is a cross-sectional view showing an end window structure of a conventional red laser device, FIG. 7 is a cross-sectional view showing an n-type GaAs cap layer forming step in the conventional semiconductor laser manufacturing method, and FIG. 8 is a conventional semiconductor laser manufacturing method. It is a surface view which shows the ZnO film formation process in FIG.

  In FIG. 6, an n-type AlGaInP cladding layer 602, an AlGaInP guide layer 603, an active layer 604, a p-type AlGaInP cladding layer 605, a p-type GaInP cladding layer 606, and a GaAs current block are formed on an n-type GaAs semiconductor substrate 601. A layer 611 and a p-type GaAs contact layer 612 are sequentially formed, and a p-side electrode 613 formed on the p-type GaAs contact layer 612 and an n-side electrode 614 formed on the back surface of the nGaAs substrate 601 are shown.

In the end face window forming step, first, an n-type GaAs cap layer 607 of a wafer having a semiconductor laminated structure as shown in FIG. 7 is processed into a stripe shape, and then a ZnO film 608 is deposited.
Next, a ZnO film 608 is formed in a stripe shape so as to be orthogonal to the n-type GaAs cap layer 607 as shown in FIG. 8, and finally Zn is diffused into the semiconductor crystal by annealing. In the region where the n-type GaAs cap layer 607 and the ZnO film 608 intersect as shown in FIG. 8, the Zn diffusion rate of the n-type GaAs cap layer 607 is slower than that of the p-type AlGaInP cladding layer 605, and Zn is directly contained in the active layer 604. Not reach. The average composition of the active layer is due to impurity re-diffusion (lateral diffusion) induced in the heavily doped region, so there is no unnecessary increase in impurity concentration and no loss due to impurity absorption in the window region. . Therefore, the diffusion shape is shallow under the GaAs cap layer as shown by the broken line in FIG. Next, ridge formation etching is performed to form a GaAs current blocking layer 611, a p-type GaAs contact layer 612 is formed, and a p-side electrode 613 and an n-side electrode 614 are formed on the back surface of the nGaAs substrate 601. It becomes a structure.
In the above example, it can be said that it is an effective means for shortening the wavelength in order to utilize the diffusion from the lateral direction without excessive Zn diffusion to the portion that becomes the light emitting region. Since the etching rate increases due to the decrease, a difference occurs in the ridge shape and height between the window portion and the gain portion, and the variation in light distribution during device operation increases (for example, see Patent Document 1).

For this purpose, ridge formation etching is performed using a ridge stripe mask (diffused through film / ZnO film / dielectric cap film structure from the bottom) that also serves as an impurity diffusion layer, and then impurity diffusion in the window region is performed by current block layer growth and contact layer growth. It has been proposed to reduce the contact resistance by making the average composition of the active layer by controlling the impurity diffusion concentration by the diffusion through film in the gain portion. Thereby, since the window is formed after the ridge is formed, the etching stop layer resistance is not deteriorated in the window region, and the ridge formation etching can be stabilized (for example, see Patent Document 2).
Japanese Patent Application Laid-Open No. 11-68217 Japanese Patent Laid-Open No. 7-162086

  However, the conventional semiconductor laser is advantageous in the resistance of the etching stop layer, but it is difficult to optimize the average composition control of the window, the mask selectivity, and the Zn diffusion control to the gain portion. It is. Particularly, the average composition is difficult to control because it depends on the current block layer growth temperature and time. Further, since the impurity diffusion layer formed in the window portion diffuses into the active layer due to the thermal history during the growth of the block layer, a non-implanted structure cannot be formed, and current leakage to the window region becomes a problem.

  Therefore, in order to solve the above-described conventional problems, the present invention performs high-precision average composition of the multiple quantum well active layer by thermal diffusion of Zn with a simple configuration even in a high-power semiconductor laser device. It is possible to ensure etching stop layer resistance.

In order to achieve the above object, a semiconductor laser device manufacturing method of the present invention includes a first conductive type cladding layer, an active layer, a second conductive type first cladding layer, and a second conductive type semiconductor substrate. An etching stop layer, a second conductivity type second cladding layer, a second conductivity type cap layer, and a second conductivity type contact layer are sequentially deposited and grown to form a semiconductor multilayer structure; and a ridge is formed on the semiconductor multilayer structure. Forming a mask pattern for forming, and etching the ridge etched by masking the second conductivity type second cladding layer, the second conductivity type cap layer and the second conductivity type contact layer with the mask pattern. forming, after the formation of the ridge, on the ridge of the end surface portion, and forming an impurity diffusion source on the ridge sides and the etching stop layer, the impurity A step of diffusing the said end face, and wherein the the step of forming a first conductivity type electrode and the second conductivity type electrode possess slope of the ridge is from 54.7 to 90 ° with respect to the bottom surface To do.

Further , the first conductivity type cladding layer, the active layer, the second conductivity type first cladding layer, the second conductivity type etching stop layer, the second conductivity type second cladding layer, and the second conductivity type are provided on the first conductivity type semiconductor substrate. A step of sequentially depositing and growing a cap layer and a second conductivity type contact layer to form a semiconductor multilayer structure; a step of forming a mask pattern for forming a ridge on the semiconductor multilayer structure; and the second conductivity type. Forming a ridge etched by masking the second cladding layer, the second conductivity type cap layer, and the second conductivity type contact layer with the mask pattern ; and after forming the ridge, on the ridge on the end surface A step of forming an impurity diffusion source, a step of diffusing the impurity into the end face portion, and a step of forming a first conductivity type electrode and a second conductivity type electrode. .

Further, the semiconductor laser device of the present invention is a semiconductor layer in which a first conductivity type cladding layer, an active layer, a second conductivity type first cladding layer, and a second conductivity type etching stop layer are stacked on a first conductivity type semiconductor substrate. And a second conductivity type second cladding layer, a second conductivity type cap layer, and a second conductivity type contact layer are stacked on the light emitting portion of the semiconductor layer, and a current injection contact layer is formed in the gain region. And a plurality of diffusion promoting ridges formed in a region adjacent to the light emitting ridge, wherein the second conductivity type second cladding layer, the second conductivity type cap layer, and the second conductivity type contact layer are laminated. And an end face window in which impurities are diffused in the end face portion, and after the formation of the light emitting portion ridge, the diffusion of the impurities is performed, and the end face window below the light emitting portion ridge is formed on the light emitting portion ridge. Not flat More deeply, the inclination of the ridge for the light emitting unit is characterized in that it is a 54.7-90 ° to the bottom surface.

The impurity is preferably Zn, Si or Mg .

Further, it is preferable that a distance between the light emitting portion ridge and the diffusion promoting ridge is 3 μm or more .

Further, it is preferable that the difference between the impurity diffusion depth at the light emitting portion ridge portion of the end face window the flat portion is 0.1μm or more.

The diffusion promoting ridge width is preferably 1 to 5 μm .

  As described above, even in a high-power semiconductor laser device, the average composition of the multiple quantum well active layer by Zn thermal diffusion can be performed with high accuracy, and the etching stop layer resistance can be ensured.

  By performing Zn diffusion after ridge formation on the light emitting part, Zn can be diffused also from the side surface of the ridge, and Zn diffusion can be concentrated on the end face of the semiconductor layer that becomes the light emitting part by low temperature, short time diffusion treatment. Even in the case of a high-power semiconductor laser device, the average composition of the multiple quantum well active layer by thermal diffusion of Zn can be performed with high accuracy and the resistance to the etching stop layer can be ensured.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, a method for manufacturing the semiconductor laser device will be described with reference to FIG.
FIG. 1 is a process cross-sectional view illustrating a method of manufacturing a semiconductor laser device according to the present invention.

  First, an n-GaAs substrate 101 is placed in a crystal growth apparatus (not shown), and as shown in FIG. 1A, n-AlGaInP is formed on the n-GaAs substrate 101 by a first crystal growth. Cladding layer 102 (thickness 2 μm), non-doped quantum well active layer 103, p-AlGaInP first cladding layer 104 (thickness 0.2 μm), etching stop layer 105, AlGaInP second cladding layer 106 (thickness 1.2 μm) The p-GaInP cap layer 107 (thickness 50 nm) and the p-GaAs contact layer 108 (thickness 0.2 μm) are sequentially deposited and grown.

  Here, the non-doped quantum well active layer 103 has a triple quantum well structure including a GaInP well layer (thickness 6 nm), an AlGaInP barrier layer (thickness 4 nm), and a guide layer (thickness 35 nm) having the same composition.

Next, a dielectric mask 109 such as SiO ₂ is formed on the semiconductor layer formed on the n-GaAs substrate 101, and a SiO ₂ mask pattern is formed as shown in FIG. 1B using a known photolithography technique. Form. Next, as shown in FIG. 1C, the p-GaAs contact layer 108, the p-GaInP cap layer 107, and the p-AlGaInP second cladding layer 106 are etched so as to reach the etching stop layer 105 to form a ridge. To do. Here, the ridge can be formed using either a dry etching technique or a wet etching technique. Dry etching is performed by inductively coupled plasma, and wet etching is performed using a hydrochloric acid-based liquid. Since impurity diffusion is not performed at this time, the crystallinity of the end face window region does not deteriorate, and there is no concern that the etching stop layer 105 is scraped due to the etching rate difference between the end face window / non-window region.

  Next, a ZnO layer 110 is formed on the semiconductor layer, and is patterned using a known photolithography technique so that the ZnO layer 110 remains only in the window region on the end face. Further, a cap film 111 is deposited as shown in FIG. Next, annealing is performed to diffuse Zn. Here, annealing is performed at about 600 ° C. for 30 minutes. Since Zn diffusion from the side wall of the ridge also occurs under the ridge, sufficient Zn is diffused even in a short annealing time.

  Next, as shown in FIG. 1E, after removing the ZnO film 110 and the dielectric mask 109, a current blocking layer 112, for example, SiN is formed, and the current injection region is formed in the gain region using a known photolithography technique. Form on the ridge. At this time, it is desirable to etch the p-GaAs contact layer 108 in the end face window region before forming the current blocking layer 112 because current leakage can be suppressed.

  Finally, a p-type ohmic electrode 113 and an n-type ohmic electrode 114 are formed as shown in FIG. 1 (f), the resonator length is adjusted to a predetermined length by a cleavage method, and reflected on the output side end face. A coating film having a reflectance of about 5% and a reflectance of about 90% is formed on the opposite end face.

  Conventionally, when a window is formed after ridge formation, the diffusion depth changes between the ridge region and other regions, so Zn may diffuse into the substrate and become electrically conductive, making diffusion controllability difficult. Furthermore, although it was difficult to evaluate the diffusion workmanship, in the semiconductor laser device produced using the manufacturing method of the present invention, the activity of the end face window portion was improved by optimizing the window conditions and establishing the evaluation method of the diffusion depth. Since the average composition of the layer 103 can be performed after the formation of the ridge, there is no ridge shape difference between the end of the Zn diffusion etching stop layer 105 and the end face window / non-window portion. In response to the demand for higher output, the wavelength of the window region, particularly the light emitting region under the end face ridge, can be further shortened (light absorption suppression). Further, in the end face window process, when Zn is diffused from the p-GaAs contact layer 108 as in the conventional method, annealing for a long time is required, and stress is required to be applied to the cap film 111 in order to perform the annealing in a short time. Although it is difficult to suppress Zn diffusion into the gain active layer, according to the present embodiment, Zn diffusion can also be performed from the side wall of the ridge. Since the composition can be performed, the diffusion of Zn into the active layer of the gain section due to excessive thermal history can also be suppressed, so that even in a high-power semiconductor laser device, the average composition of the multiple quantum well active layer by thermal diffusion of Zn Can be performed with high accuracy and resistance to the etching stop layer can be ensured.

Next, the end face window forming step of the present invention will be described in detail with reference to FIGS.
FIG. 2 is a view for explaining an end face window forming step in the method for manufacturing a semiconductor laser device of the present invention, and FIG. 3 is a view for explaining an end face window forming step in which a source is formed on a ridge in the method for manufacturing a semiconductor laser device of the present invention. 4 is a cross-sectional view illustrating a semiconductor laser device according to the present invention, and FIG. 5 is a cross-sectional view illustrating a semiconductor laser device having a plurality of ridges according to the present invention.

  First, as shown in FIG. 2, after the ridge is formed, a ZnO layer 110 is formed in a region that becomes a window near the end face, and a cap film 111 is formed and annealed. An impurity diffusion source (hereinafter referred to as source) position at the time of diffusion is formed so as to be in contact with the entire surface of the ridge portion and the flat portion. The Zn diffusion direction is mainly in the direction of the arrow shown in the figure. However, since the diffusion to (111), which is the closest-packed surface of the crystal, is large at the time of annealing, the Zn profile is around the ridge below the light emitting region. It becomes deeper than the depth a and is particularly averaged in the light emitting region, and light absorption from the gain portion active layer can be suppressed by increasing the band gap.

  As shown in FIG. 3, when the ZnO layer 110 which is a Zn source is formed in the ridge top portion, the diffusion proceeds from the ridge to the active layer 103, so that the Zn diffusion under the ridge is deep. However, in this case, since the region where the average composition of the active layer 103 is about the ridge width, light is absorbed outside the diffusion region.

  Therefore, as shown in FIG. 2, it is preferable to use diffusion from the ridge slope and diffusion from a flat portion near the bottom of the ridge. Through such a window process, vertical and oblique Zn diffusion from the ridge is performed, so that the difference between the Zn depth of the flat portion without the ridge and the Zn diffusion depth of the ridge portion as shown in FIG. Becomes deeper than 0.1 μm.

  Here, it is preferable that the inclination angle of the ridge is within 54.7 ° to 90 ° which can promote diffusion in the (111) direction. Further, it is considered that the same effect can be obtained when the impurity as a diffusion source is Mg, Si or the like in addition to Zn.

  Structural example 1 of the semiconductor element manufactured by the window process will be described. FIG. 4A is a cross-sectional view of the window region of Structural Example 1, and is characterized in that Zn diffusion is deep under the ridge. Since Zn diffusion is deep in the lower part of the ridge, the average composition is particularly obtained in the light emitting region, and light absorption from the gain active layer is suppressed by increasing the band gap. Further, the window ridge is covered with the current blocking layer 112 to prevent current leakage. FIG. 4B is a cross-sectional view of the gain region of Structural Example 1. The p-GaAs contact layer 108 is left above the ridge so that current can be injected into the active layer 103.

  FIG. 5 shows Structural Example 2. A plurality of ridges 116 for promoting diffusion are formed so as to sandwich the ridges 115 for the light emitting portion. A p-GaAs contact layer 108 for injecting a current after Zn diffusion is formed on the ridge 115 for the light emitting portion in the gain region. Thus, by forming a plurality of ridges and utilizing the effect of Zn diffusion from the ridge slope during annealing, a stable window structure that can promote diffusion over a wide region as shown in FIG. Can be obtained. At this time, the distance between the ridge 115 for the light emitting portion and the ridge 116 for promoting diffusion is such that when the ridge is formed by wet etching, the ridge shape has a base corresponding to (111). It is desirable that the distance is 3 μm or more so that the bottom does not touch. In addition, since the Zn source has a large diffusion effect from the ridge slope (111), the lateral diffusion is observed from about the same to twice the ridge height of 1.2 μm (1 to 2.5 μm). It is done. Since the ridge is formed by left and right slopes, the width of the ridge 116 for promoting diffusion is preferably about 1 to 5 μm. In addition, the provision of the diffusion promoting ridge 116 is also effective in relieving assembly stress for the light emitting portion ridge 115 serving as the light emitting portion.

  As shown in FIG. 5B, which is a cross-sectional structure diagram of the gain region, a p-GaAs contact layer 108 is formed on the ridge 115 for the light emitting section so as to inject current only into the ridge 115 for the light emitting section. . If the annealing temperature is too high, Zn diffusion will occur up to the GaAs substrate 101 and electrical conduction will result in no laser oscillation. Therefore, it is desirable that the conditions be within a range of 400 ° C. to 750 ° C., which allows easy control of diffusion.

  In this embodiment, since Zn diffusion is performed after the ridge is formed on the light emitting portion, Zn diffusion can also be concentrated on the end surface of the active layer 103 serving as the light emitting portion by Zn diffusion from the side surface of the ridge. Concentration control is important. The average composition with an excessive Zn concentration causes crystal defects, and it is highly likely to cause end face damage due to light absorption by non-radiative recombination centers and free carriers. Therefore, the active layer Zn concentration is within 4E18 cm −3. Something is desirable.

  As described above, according to the present embodiment, the example using the AlGaInP-based material used in the red laser has been introduced, but the conditions for the AlGaAs-based material used in the infrared laser are different, but the end face window is formed in the same manner. Needless to say, it can be formed. It is also possible to change the conductivity type.

  As described above, according to the semiconductor laser device according to the present invention, in the ridge type semiconductor laser having the end face window structure corresponding to the high output, the transparent average and stable average composition at the lower part of the ridge which is the light emitting region. Can be done. In addition, the ridge formation process can be performed before the end face window formation (impurity diffusion), and the ridge shape of the end face window / gain region is stabilized without any difference due to crystallinity degradation. Can be stabilized. In addition, since etching stop omission is suppressed, the etching stop layer can be made thinner, light absorption from the active layer can be reduced, and the structure can cope with higher output. Furthermore, since the end face window can be formed in a short time without an excessive heat history, the reliability can be improved. Therefore, according to the present invention, even in a high-power semiconductor laser device, the average composition of the multiple quantum well active layer by thermal diffusion of Zn can be performed with high accuracy and the etching stop layer resistance can be ensured. Can do.

  Even if the present invention is a high-power semiconductor laser device, the average composition of the multi-quantum well active layer by thermal diffusion of Zn can be performed with high accuracy and the resistance to the etching stop layer can be ensured. It is useful for a semiconductor laser device having an element structure necessary for achieving high output and highly reliable operation performance, a manufacturing method of the semiconductor laser device, and the like.

Process sectional drawing explaining the manufacturing method of the semiconductor laser apparatus of this invention The figure explaining the end surface window formation process in the manufacturing method of the semiconductor laser apparatus of this invention The figure explaining the end face window formation process which formed the source on the ridge in the manufacturing method of the semiconductor laser apparatus of this invention Sectional drawing explaining the semiconductor laser apparatus of this invention Sectional drawing explaining the semiconductor laser apparatus which comprised the several ridge of this invention Sectional view showing the end face window structure of a conventional red laser device Sectional drawing which shows the n-type GaAs cap layer formation process in the manufacturing method of the conventional semiconductor laser Surface view showing a ZnO film forming process in a conventional semiconductor laser manufacturing method

Explanation of symbols

101 n-GaAs substrate 102 n-AlGaInP cladding layer 103 active layer 104 p-AlGaInP first cladding layer 105 etching stop layer 106 AlGaInP second cladding layer 107 p-GaInP cap layer 108 p-GaAs contact layer 109 dielectric mask 110 ZnO Layer 111 cap film 112 current blocking layer 113 p-type ohmic electrode 114 n-type ohmic electrode 115 ridge for light emitting portion 116 ridge for diffusion promotion 601 n-type GaAs semiconductor substrate 602 n-type AlGaInP cladding layer 603 AlGaInP guide layer 604 active layer 605 p-type AlGaInP clad layer 606 p-type GaInP clad layer 607 n-type GaAs cap layer 608 ZnO film 611 GaAs current blocking layer 612 p GaAs contact layer 613 p-side electrode 614 n-side electrode

Claims (7)

A first conductivity type cladding layer, an active layer, a second conductivity type first cladding layer, a second conductivity type etching stop layer, a second conductivity type second cladding layer, and a second conductivity type cap layer on a first conductivity type semiconductor substrate And sequentially depositing and growing a second conductivity type contact layer to form a semiconductor multilayer structure;
Forming a mask pattern for forming a ridge on the semiconductor multilayer structure;
Forming the ridge etched by masking the second conductivity type second cladding layer, the second conductivity type cap layer and the second conductivity type contact layer with the mask pattern;
Forming an impurity diffusion source on the ridge at the end face, on the ridge side surface and on the etching stop layer after forming the ridge ;
Diffusing the impurities into the end face portion;
The method of manufacturing a semiconductor laser device which have a forming a first conductivity type electrode and the second conductivity type electrode, the inclination of the ridge is characterized in that it is a from 54.7 to 90 ° with respect to the bottom surface. A first conductivity type cladding layer, an active layer, a second conductivity type first cladding layer, a second conductivity type etching stop layer, a second conductivity type second cladding layer, and a second conductivity type cap layer on a first conductivity type semiconductor substrate And sequentially depositing and growing a second conductivity type contact layer to form a semiconductor multilayer structure;
Forming a mask pattern for forming a ridge on the semiconductor multilayer structure;
Forming the ridge etched by masking the second conductivity type second cladding layer, the second conductivity type cap layer and the second conductivity type contact layer with the mask pattern;
Forming an impurity diffusion source on the ridge at the end face after the formation of the ridge ;
Diffusing the impurities into the end face portion;
And a step of forming a first conductivity type electrode and a second conductivity type electrode. A semiconductor layer in which a first conductivity type cladding layer, an active layer, a second conductivity type first cladding layer, and a second conductivity type etching stop layer are stacked on a first conductivity type semiconductor substrate;
For a light emitting unit in which a second conductivity type second cladding layer, a second conductivity type cap layer, and a second conductivity type contact layer are stacked on the light emitting unit of the semiconductor layer, and a contact layer for current injection is formed in the gain region Ridge,
A plurality of diffusion promoting ridges formed in a region adjacent to the light emitting ridge, wherein a second conductivity type second cladding layer, a second conductivity type cap layer, and a second conductivity type contact layer are laminated;
And an end face window diffused impurities into the end face, the diffusion of the impurity is performed after the ridge is formed for the light emitting portion, said end face window of the ridge lower for the light emitting portion is no ridge for the light emitting portion the semiconductor laser device, wherein the deeply than the flat portion, the inclination of the ridge for the light emitting portion is a 54.7-90 ° to the bottom surface. 4. The semiconductor laser device according to claim 3, wherein the impurity is Zn, Si, or Mg . 4. The semiconductor laser device according to claim 3, wherein a distance between the light emitting portion ridge and the diffusion promoting ridge is 3 [mu] m or more . 4. The semiconductor laser device according to claim 3 , wherein a difference in impurity diffusion depth between the light emitting portion ridge portion and the flat portion of the end face window is 0.1 μm or more . 6. The semiconductor laser device according to claim 3, wherein the diffusion promoting ridge width is 1 to 5 [mu] m .

Images