JP2006093682A - Semiconductor laser and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser having an improved ridge that does not lower the luminous efficiency by an etching stopper layer, and a method for manufacturing the same.
A semiconductor laser that does not use an etching stopper or a semiconductor laser that uses an etching stopper that does not lower the light emission efficiency is proposed. The ridge is formed by an etching process for etching the third cladding layer. This etching process includes a first etching process for performing dry etching and a second etching process for performing wet-watching. In the first etching step, the third cladding layer is dry-etched up to just above the second cladding layer, and in the second etching step, the final etching is performed.
[Selection] Figure 2

Description

  The present invention relates to a semiconductor laser having a ridge used for an optical disc system or optical communication.

  As semiconductor lasers having this type of ridge, there are a ridge type semiconductor laser and a ridge embedded type semiconductor laser. The ridge type semiconductor laser is configured such that grooves are formed on both sides of the ridge and current is concentrated on the ridge. Further, the ridge embedded semiconductor laser is configured such that current blocking layers are formed on both sides of the ridge so that current is concentrated on the ridge.

  The ridge type semiconductor laser is disclosed in Japanese Patent Application No. 2003-21319 (Japanese Patent Laid-Open No. 2004-235382) by the same inventor as this application. The ridge type semiconductor laser disclosed in Japanese Patent Application No. 2003-21319 has a lower cladding layer, an active layer having a multiple quantum well structure, a first upper cladding layer, an etching stopper layer, a second layer on an n-type GaAs substrate. An upper clad layer is sequentially laminated, a ridge is formed at the center of the second upper clad layer, and a groove is formed on both sides thereof. The etching stopper layer is arranged to stop the etching for forming the ridge in the second upper cladding layer by the etching stopper layer.

  A ridge embedded semiconductor laser is disclosed in Japanese Patent Application Laid-Open No. 2003-69154. In the ridge embedded semiconductor laser disclosed in Japanese Patent Application Laid-Open No. 2003-69154, the ridge is formed by dry etching and subsequent wet etching, but has an etching stop layer to stop the wet etching. .

  In addition, when forming a ridge by wet etching, it is necessary to use a material having a wet etching rate smaller than that of the cladding layer for the etching stopper layer, but such a material is not found in the blue laser, Usually, a structure having no etching stopper layer as described above is used. In JP 2000-294875 A, an insulating film having a stripe-shaped opening is formed on the first p-type nitride semiconductor layer on the active layer without using an etching stopper layer, and the opening is formed on the opening. 2 discloses a method in which a second nitride semiconductor layer is grown to form a ridge.

Application for Japanese Patent Application No. 2003-21319 JP 2003-69154 A JP 2000-294875 A

  As described above, each of the semiconductor lasers disclosed in Patent Documents 1 and 2 uses an etching stopper layer or an etching stop layer. Moreover, the etching stopper layer of Patent Document 1 has an Al composition ratio smaller than that of the lower cladding layer, the first upper cladding layer, and the second cladding layer. The etching stop layer of Patent Document 2 is composed of GaAs, GaInP, or AlGaInP that does not contain Al, and the Al composition ratio is considered to be small. Since the etching stopper layer or the etching stop layer has a large refractive index, the light distribution is biased toward the etching stopper layer or the etching stop layer, which causes a problem that the luminous efficiency is lowered and the characteristics are deteriorated.

In Patent Document 3, an etching stopper layer is not used, but it is necessary to perform semiconductor growth twice before and after the formation of the insulating film, resulting in a problem that productivity is lowered.

  The present invention proposes an improved semiconductor laser capable of improving such problems and a method for manufacturing the same.

  According to a first aspect of the present invention, there is provided a semiconductor laser comprising: a first conductivity type first cladding layer formed on a first conductivity type semiconductor substrate; an active layer formed on the first cladding layer; A second conductivity type second clad layer formed on the active layer; and a second conductivity type third clad layer formed on the second clad layer, wherein at least the third clad layer has a ridge The third laser diode is formed by directly bonding the third cladding layer on the second cladding layer.

  According to a second aspect of the present invention, there is provided a semiconductor laser comprising: a first conductivity type first cladding layer formed on a first conductivity type semiconductor substrate; and an active layer formed on the first cladding layer. A second conductivity type second cladding layer containing Al formed on the active layer, an etching stopper layer containing Al formed on the second cladding layer, and formed on the etching stopper layer A semiconductor laser having a second conductivity type third cladding layer containing Al and having a ridge formed in the third cladding layer, wherein an Al composition ratio of the etching stopper layer is Al in the third cladding layer. It is characterized by being larger than the composition ratio.

  According to a first aspect of the present invention, there is provided a semiconductor laser manufacturing method comprising: a first conductivity type first cladding layer formed on a first conductivity type semiconductor substrate; and the first cladding layer formed on the first cladding layer. An active layer; a second conductivity type second clad layer formed on the active layer; and a second conductivity type third clad layer formed by direct bonding on the second clad layer. A method of manufacturing a semiconductor laser in which a ridge is formed at least in the third cladding layer, the method including an etching step of forming the ridge, wherein the etching step places the third cladding layer near the second cladding layer. A first etching step for dry etching to a predetermined thickness, and a second etching step for wet etching the third cladding layer after the first etching step.

  Furthermore, the semiconductor laser manufacturing method according to the second aspect of the present invention includes a first conductivity type first cladding layer formed on a first conductivity type semiconductor substrate and the first cladding layer formed on the first cladding layer. An active layer, a second conductivity type second cladding layer containing Al formed on the active layer, an etching stopper layer containing Al formed on the second cladding layer, and an etching stopper layer on the etching stopper layer A third clad layer of the second conductivity type containing Al formed, wherein the Al composition ratio of the etching stopper layer is larger than the Al composition ratio of the third clad layer, and a ridge is formed in the third clad layer. A method of manufacturing a formed semiconductor laser, comprising: an etching step of forming the ridge, wherein the etching step includes bringing the third cladding layer to a predetermined thickness near the etching stopper layer. A first etching step of dry etching, characterized in that it comprises a second etching step of wet-etching the third cladding layer to the etching stopper layer after this first etching step is exposed.

  In the semiconductor laser according to the first aspect of the present invention, the second conductivity type third cladding layer formed on the second conductivity type second cladding layer is formed by being directly bonded to the second cladding layer. In addition, there is no conventional etching stop layer between the second cladding layer and the third cladding layer. Therefore, the etching stop layer prevents the light distribution from being biased toward the etching stop layer, thereby improving the light emission efficiency and obtaining a semiconductor laser having a higher light output.

  In the semiconductor laser according to the second aspect of the present invention, the etching stopper layer containing Al formed on the second clad layer of the second conductivity type containing Al has the second conductivity containing Al formed thereon. Since the Al composition ratio is larger than that of the third cladding layer of the mold, the deviation of the light distribution due to this etching stopper layer is reduced, the light emission efficiency is improved, and a semiconductor laser having a higher light output can be obtained.

  In the method of manufacturing a semiconductor laser according to the first aspect of the present invention, the etching step for forming the ridge includes a first etching step for dry-etching the third cladding layer close to the second cladding layer, and the first etching step. A second etching step of performing wet etching on the third cladding layer after the etching step, and in the second etching step, the remaining third cladding layer can be wet etched with sufficient controllability, As a result, since the ridge can be formed without using an etching stopper layer, the light distribution is not biased toward the etching stop layer, the light emission efficiency is improved, and a semiconductor laser having a higher light output is obtained. be able to. Further, the first cladding layer, the active layer, the second and third cladding layers can be formed with high productivity in a single crystal growth process.

  Further, in the method of manufacturing a semiconductor laser according to the second aspect of the present invention, the etching step for forming the ridge includes a first etching step for dry etching the third cladding layer to a predetermined thickness, and a step after the first etching step. Since the second etching process includes wet etching the third cladding layer until the etching stopper layer is exposed, the etching stopper layer is exposed in the second etching process after performing the etching efficiently in the first etching process. In addition, an etching stopper layer containing Al is used, and this etching stopper layer has a larger Al composition ratio than the third cladding layer of the second conductivity type containing Al. , Improving the light distribution biased toward this etching stopper layer, better luminous efficiency, Ri can be obtained the semiconductor laser of high light output. Further, the first cladding layer, the active layer, the second cladding layer, the etching stopper layer, and the third cladding layer can be formed with high productivity in a single crystal growth process.

  Several embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 FIG.
FIG. 1 is a partially cutaway perspective view showing a first embodiment of a semiconductor laser according to the first aspect of the present invention, and FIG. 2 is a cross-sectional view taken along line AA. The semiconductor laser of the first embodiment is a ridge type semiconductor laser, specifically, a ridge type semiconductor red light emitting laser.

  The semiconductor laser 10 according to the first embodiment is formed in a thin and substantially rectangular shape, and has a pair of opposite end faces 11 and 12 and a pair of opposite side faces 13 and 14. End faces 11 and 12 are light emitting end faces. A striped ridge 15 is formed in the center of the upper surface of the semiconductor laser 10. The ridge 15 is formed so as to extend between the end surface 11 and the end surface 12. A pair of grooves 16 and 17 are formed on both sides of the ridge 15 along the ridge 15, and a pair of side walls 18 and 19 are formed on both sides of the grooves 16 and 17.

  The semiconductor laser 10 is manufactured using a semiconductor substrate 20 made of n-type GaAs. A first clad layer 21 made of n-type AlGaInP is formed on the semiconductor substrate 20 so as to be directly bonded to the semiconductor substrate 20, and an active layer 22 is formed on the first clad layer 21. It is formed so as to be directly bonded to the layer 21. The active layer 22 has a multiple quantum well structure (MQW structure) using GaInP as a well layer and AlGaInP as a barrier layer. A second cladding layer 23 made of p-type AlGaInP is formed on the active layer 22 so as to be directly bonded to the active layer 22, and further, on the second cladding layer 23, it is made of p-type AlGaInP. The third cladding layer 24 is formed so as to be directly bonded to the second cladding layer 23.

The semiconductor substrate 20, the first cladding layer 21, the active layer 22, the second cladding layer 23, and the third cladding layer 24 are formed so as to be exposed at the end surfaces 11 and 12 and the side surfaces 13 and 14. The first cladding layer 21 has a thickness of 1.5 to 4.0 μm and a carrier concentration of 0.3 to 0.8 × 10 ¹⁸ cm ⁻³ . The thickness of the second cladding layer 23 is 0.1 to 1.0 μm, and the carrier concentration is 0.3 to 1.0 × 10 ¹⁸ cm ⁻³ . The third cladding layer 24 has a thickness of 0.5 to 2.0 μm and a carrier concentration of 0.3 to 1.0 × 10 ¹⁸ cm ⁻³ .

The composition of AlGaInP constituting each of the cladding layers 21, 23, 24 is precisely (Al _x Ga _1-x ) _0.5 In _0.5 P, and each of the cladding layers 21, 23, 24 is made of Al The composition ratio _x is 0.5 to 0.7.

  The third cladding layer 24 constitutes a striped ridge 15 and a pair of side walls 18 and 19. Grooves 16 and 17 are formed between the ridge 15 and the pair of side walls 18 and 19 by an etching process. Grooves 16 and 17 are formed in the third cladding layer 24 by an etching process, and the ridge 15 and the pair of side walls 18 and 19 are separated by the grooves 16 and 17. The grooves 16 and 17 are formed at a depth penetrating at least the third cladding layer 24. The depths of the grooves 16 and 17 are formed so as to reach the surface of the second cladding layer 23 or the surface portion of the second cladding layer 23.

  A window region 25 is formed on the end faces 11 and 12 of the semiconductor laser 10. The window region 25 is formed at a depth reaching the first cladding layer 21 from the third cladding layer 24 through the second cladding layer 23 and the active layer 22. The window region 25 is formed in a portion adjacent to the end faces 11 and 12 by Zn diffusion or the like, and disordered the active layer 22.

A contact layer 26 made of p-type GaAs is formed on the top surface of the ridge 15. Both side surfaces of the ridge 15, bottom surfaces of the grooves 16 and 17, side surfaces adjacent to the grooves 16 and 17 of the side walls 18 and 19, and top surfaces of the side walls 18 and 19 are covered with an insulating film 27 such as a silicon nitride film. A p-side electrode 28 is formed on the insulating film 27, and the p-side electrode 28 is bonded to the contact layer 26 with a low resistance. An n-side electrode 29 is joined to the bottom of the semiconductor substrate 20.
The semiconductor laser 10 generates a light output L from the end faces 11 and 12 by supplying a drive current from the p-type electrode 28 to the n-type electrode 29.

  Now, a manufacturing method of the semiconductor laser according to the first embodiment will be described. First, a semiconductor substrate 20 made of n-type GaAs is prepared. A first cladding layer 21, an active layer 22, a second cladding layer 23, a third cladding layer 24, and a contact layer 26 are sequentially formed on the GaAs substrate 20 by a crystal growth method such as MOCVD. In this state, the first cladding layer 21, the active layer 22, the second cladding layer 23, the third cladding layer 24, and the contact layer 26 are sequentially stacked on the upper surface of the rectangular semiconductor substrate 20.

  Next, in the vicinity of the end faces 11 and 12, Zn or the like is selectively diffused from the upper surface to form the window region 25. Subsequently, the contact layer 26 is selectively removed by etching so that the contact layer 26 remains only on the top surface of the ridge 15. In this state, an etching process for forming the ridge 15 and the pair of side walls 18 and 19 in the third cladding layer 24 is performed.

  This etching process is a selective etching for forming the grooves 16 and 17 in the third cladding layer 24, and this etching process includes a first etching process for performing dry etching and a second etching process for performing wet etching thereafter. . This etching process is performed following the etching of the contact layer 26, and grooves 16 and 17 are formed in the third cladding layer 24 in a state where the top surface of the ridge 15 and the top surfaces of the pair of side walls 18 and 19 are masked. To do. In this etching process, a first etching process that performs dry etching is performed first, and then a second etching process that performs wet etching is performed.

  In the first etching step, the third cladding layer 24 is dry-etched up to just above the second cladding layer 23. The thickness remaining in the third cladding layer 24 in the state where the first etching step is completed is referred to as the remaining thickness. In the second etching step, following the first etching step, the third cladding layer 24 is wet etched as a final etching to remove the remaining thickness. The dry etching in the first etching step has little side etching and is effective for making the side surface of the ridge 15 a substantially vertical side surface. The wet etching in the second etching step is effective for removing damage on the etched surface due to the dry etching in the first etching step.

  The remaining thickness of the third cladding layer 24 left in the first etching step is set in advance to a predetermined set value. The allowable range of the set value of the remaining thickness is 0 nm to 200 nm, and a preferable preferable range within the allowable range is a range of 10 nm to 100 nm. The preferable range of 10 nm to 100 nm is to remove the damage due to the dry etching in the first etching process sufficiently by the wet etching in the second etching process, and to prevent the influence of the variation in the wet etching in the second etching process from remaining. For the range. When the remaining thickness is 0 nm, the surface portion of the second cladding layer 23 is slightly etched by the wet etching in the second etching step, and the grooves 16 and 17 reach the surface portion of the second cladding layer 23. Become.

  In a specific example of the first embodiment, the set value of the remaining thickness is set to a thickness of 30 nm within the preferable range. If the thickness of the third cladding layer 24 is, for example, 1 μm, 97% of the thickness is etched in the first etching step. In the first embodiment, the remaining thickness is monitored and controlled by irradiating laser light from the laser device.

  Specifically, a laser device is arranged on the upper part of the semiconductor laser 10 that is being manufactured, and laser light from the laser device is irradiated toward the semiconductor substrate 20. Using the laser light irradiated toward the semiconductor substrate 20 as incident light, the etched thickness of the third cladding layer 24 is measured based on interference between the incident light and reflected light from the active layer 22. From this etching thickness, the remaining thickness is monitored and controlled. As a result, the remaining thickness is controlled to a predetermined set value, and in the specific example of the first embodiment, when the remaining thickness reaches the set value 30 nm, the dry etching by the first etching process is finished. .

The dry etching in the first etching process is performed, for example, using an ICP plasma etching apparatus, using SiCl ₄ / Ar gas as an etching gas, and a pressure of about 0.5 Pa.

  After the first etching step is completed, the semiconductor laser 10 being manufactured is immersed in a wet etching solution, and the second etching step for the third cladding layer 24 is performed. For example, hydrofluoric acid is used as the wet etching solution.

  The wet etching by the second etching process is performed for the etching time necessary for etching the remaining thickness in accordance with the remaining thickness of the third cladding layer 24 by the first etching process. Is done. In the specific example of the first embodiment, since the remaining thickness is set to 30 nm, the wet etching time in the second etching step is set to the time for etching the remaining thickness of 30 nm.

  When the remaining thickness is set to 0 nm, the etching time in the second etching process is, for example, 5-10 nm wet etching in order to remove damage on the etching surface due to dry etching in the first etching process. The etching time is set so that.

  After the etching process is completed, an insulating film 27 is deposited on the entire upper surface of the semiconductor laser 10, and the insulating film 27 is removed by etching at the top surface portion of the ridge 15 to expose the contact layer 26. Thereafter, the p-side electrode 28 and the n-side electrode 29 are formed.

  FIG. 3 is a graph showing the refractive index and light output distribution of the semiconductor laser according to the first embodiment. In FIG. 3, the horizontal axis indicates the position in the thickness direction of the semiconductor laser 10. A curved line 30 indicates a refractive index, and a central uneven portion 31 indicates a refractive index changing portion corresponding to the active layer 22. A curve 35 shows a light output distribution corresponding to the change in the refractive index, and has a peak 36 at a portion corresponding to the active layer 22, and is a gentle curve that is substantially symmetrical on both sides of the peak 36. .

  For comparison with FIG. 3, FIG. 4 is a graph showing the refractive index and the light output distribution of the conventional ridge type semiconductor laser as in FIG. Since the conventional semiconductor laser has an etching stopper layer having a refractive index larger than that of each of the cladding layers 21, 23, and 24, as shown in FIG. 4, the left side of the uneven portion 31, that is, the upper surface of the uneven portion 31. On the side, it has a maximum portion 32 of refractive index. This maximum is the refractive index of the etching stopper layer. In the conventional semiconductor laser, since the maximum portion 32 exists in the refractive index, the maximum portion 37 appears in the light output distribution, and the light output distribution 35 is on the maximum portion 37 side, that is, on the p-type cladding layer side where free carrier absorption is large. Biased. For this reason, the light emission efficiency is lowered and the light emission characteristics are deteriorated.

  In the first embodiment, since the etching stopper layer or the etching stop layer used conventionally is not used, the light output distribution is not biased toward the maximum portion 37 side, and the light output distribution has a peak 36 as shown in FIG. Is substantially symmetrical on both sides of the peak 36, and both sides of the peak 36 are gentle curves, so that the light emission output can be increased and the light emission efficiency can be improved. In the first embodiment, since the layers 21 to 24 and 26 are stacked and crystal-grown on the semiconductor substrate 20, the layers 21 to 24 and 26 can be formed by a single crystal growth step. And productivity can be improved.

  Even in a conventional semiconductor laser having an etching stopper layer or an etching stop layer, if the light output is about 50 mW, a decrease in light emission efficiency is not recognized, but if the light output is in a high-power laser exceeding 100 mW, the etching stopper layer Alternatively, a decrease in luminous efficiency due to the etching stop layer becomes a problem. In particular, in a long cavity laser with a large internal loss ratio in which the cavity length is set to 1000 μm or more in order to increase the output, the light emission efficiency is remarkably lowered. In Embodiment 1 of the present invention, even in such a high-power laser, particularly a long cavity laser, it is possible to eliminate a decrease in light emission efficiency due to the etching stopper layer or the etching stop layer.

  FIG. 5 shows the light output characteristics of the semiconductor laser 10, wherein the horizontal axis represents the drive current (mA) and the vertical axis represents the light output (mW). FIG. 5 shows the optical output with respect to the current obtained by calculation. A curve 40 is an optical characteristic of the semiconductor laser 10 according to the first embodiment, and a curve 41 is an optical characteristic of a conventional ridge type semiconductor laser having an etching stopper layer for comparison. In the first embodiment, as shown by the curve 40, the light output increases as compared with the curve 41, and the light output increases more particularly in the region where the drive current is large.

  In the first embodiment, the upper portion of the semiconductor laser 10 is irradiated with the laser light from the laser device, and the first etching process is performed based on the interference between the incident light on the semiconductor laser 10 and the reflected light from the active layer 22. The etching thickness of the third cladding layer 24 by dry etching is measured and the remaining thickness is monitored. Based on the interference between the incident light and the reflected light from the semiconductor substrate 20, the dry etching in the first etching step is performed. It is also possible to measure the etching thickness of the third cladding layer 24 and monitor the remaining thickness. Further, when the compositions of the second cladding layer 23 and the third cladding layer 24 are different from each other, the third cladding layer changes from the change in the reflected light based on the difference in reflectance between the cladding layers 23 and 24. It is also possible to determine the end point of the dry etching in the first etching step by measuring the etching thickness of the layer 24 and the remaining thickness thereof.

Embodiment 2. FIG.
6 is a perspective view showing a second embodiment of a semiconductor laser according to the second aspect of the present invention, with a part cut away, and FIG. 7 is a sectional view taken along line BB. The semiconductor laser of the second embodiment is also a ridge type semiconductor laser, specifically, a ridge type semiconductor red light emitting laser.

  The semiconductor laser 10A according to the second embodiment has an etching stopper layer 234 between the second cladding layer 23 and the third cladding layer 24. The etching stopper layer 234 is the third cladding layer 24. It has a larger Al composition ratio and its refractive index is small.

Specifically, the etching stopper layer 234 is made of AlInP and has a thickness of 20 nm. The first cladding layer 21, the second cladding layer 23, and the third cladding layer 24 are the same as those in the first embodiment. The first cladding layer 21 is made of n-type (Al _x Ga _1-x ) _0.5 In _0.5 P, and its Al composition ratio is 0.5 to 0.7, and the impurity carrier concentration is 0.3. -0.8 * 10 < ¹⁸ > cm < ^-3 >, thickness is 1.5-4.0 micrometers. The second cladding layer 23 is made of p-type (Al _x Ga _1-x ) _0.5 In _0.5 P, and the Al composition ratio _x is 0.5 to 0.7, and the impurity carrier concentration is 0.3. -1.0 * 10 < ¹⁸ > cm < ^-3 >, thickness is 0.1-1.0 micrometer. The third cladding layer 24 is made of p-type (Al _x Ga _1-x ) _0.5 In _0.5 P, the Al composition ratio _x is 0.5 to 0.7, and the impurity carrier concentration is 0. .3-1.0 × 10 ¹⁸ cm ⁻³ and thickness is 0.5-2.0 μm. The Al composition ratio of the etching stopper layer 234 is larger than the Al composition ratio of the third cladding layer 24 and is in the range of 0.5 to 1.0. Specifically, the second and third cladding layers 23 and 24 are in the range of 0.5 to 1.0. The Al composition ratio is 0.6, and the Al composition ratio of the etching stopper layer 234 is 0.8.

  Also in the second embodiment, the etching process for forming the grooves 16 and 17 in the third cladding layer 24 is performed in the same manner as in the first embodiment. This etching process is performed by dry etching in the first etching process until the remaining thickness of the third cladding layer 24 reaches, for example, 30 nm within an allowable range of 0 to 200 nm and a preferable range of 10 to 100 nm, and thereafter For the finishing, wet etching is performed in the second etching step. The etching stopper layer 234 stops the wet etching in the second etching process, and stops the wet etching in the second etching process when the etching stopper layer 234 is exposed from the grooves 16 and 17.

  In the second embodiment, the upper part of the semiconductor laser 10A is irradiated with laser light from the laser device, and based on the difference in the reflected light from the third cladding layer 24 and the etching stopper layer 234, the first etching process is performed by dry etching. The etching thickness of the 3 clad layer 24 is measured, and the remaining thickness is monitored. However, based on the interference between the incident light from the laser device and the reflected light from the active layer 22 or the reflected light from the semiconductor substrate 20, the etching thickness of the third cladding layer 24 by dry etching in the first etching step is reduced. It is also possible to measure and monitor the remaining thickness.

  The embodiment is the same as the embodiment except that the etching stopper layer 234 is disposed and the etching thickness of the third cladding layer 24 is measured based on the difference in reflected light from the third cladding layer 24 and the etching stopper layer 234. 2 is formed in the same manner as in the first embodiment, and is manufactured by the same method as in the first embodiment.

  FIG. 8 is a graph showing the refractive index and light output distribution of the semiconductor laser according to the second embodiment. In FIG. 8, the horizontal axis indicates the position in the thickness direction of the semiconductor laser 10A. Similar to FIG. 3, the curve 30 indicates the refractive index, the central uneven portion 31 indicates the refractive index changing portion corresponding to the active layer 22, and the left side of the uneven portion 31 is the refractive index corresponding to the etching stopper layer 234. It has a small portion 34. A curve 35 shows a light output distribution corresponding to this change in refractive index, has a peak 36 at a portion corresponding to the active layer 22, and is a gentle curve that is substantially symmetrical on both sides of the peak 36.

  Although the second embodiment has the etching stopper layer 234, the Al composition ratio of the etching stopper layer 234 is larger than that of the third cladding layer 24 and the refractive index is smaller than that of the third cladding layer 24. As shown by the curve 35, the light output distribution is not biased toward the etching stopper layer 234 because it is almost symmetrical and gentle on both sides of the peak 36. As in the first embodiment, the light emission efficiency is increased, The output characteristics can be improved. In the second embodiment, since the layers 21 to 23, 234, 24, and 26 are stacked and crystal-grown on the semiconductor substrate 20, the layers 21 to 23, 234, 24, and 26 are formed once. It can be formed by a crystal growth step, and productivity can be improved.

  The first and second embodiments are ridge-type red semiconductor lasers, but are ridge-type semiconductor lasers in which the free carrier absorption of the p-type cladding layers 23 and 24 affects the light output distribution, and the lateral fundamental mode oscillation. Therefore, the present invention can be similarly applied to a 980 nm semiconductor laser, a blue laser, and the like whose ridge width and ridge shape need to be controlled. In this case, since the ridge width is narrow and a vertical ridge can be formed, a semiconductor laser having a high king level can be obtained. In addition to the ridge type semiconductor laser, the present invention can be similarly applied to a ridge embedded type semiconductor laser.

  For example, in a 980 nm semiconductor laser, the semiconductor substrate 20 is composed of GaAs, the first cladding layer 21 is composed of n-type AlGaAs, and the second and third cladding layers 23 and 24 are composed of p-type AlGaAs. In this 980 nm semiconductor laser, as in the first embodiment, the third cladding layer 24 is directly bonded to the second cladding layer 23, and the etching stopper layer therebetween is not used, or the same as in the second embodiment. A configuration is adopted in which the Al composition ratio of the etching stopper layer 234 is made larger than the Al composition ratio of the third cladding layer 24 while using the etching stopper layer 234.

  In addition, each of the above embodiments constitutes the semiconductor lasers 10 and 10A with a single semiconductor chip, but is similarly applied to a high-power 800-1000 nm band array laser in which a plurality of semiconductor chips are arranged. it can. In this case, since the light emission efficiency is improved, an array laser with a small operating current can be obtained.

Embodiment 3 FIG.
FIG. 9 is a cross-sectional view of the central portion including the ridge of the nitride semiconductor laser according to the third embodiment of the present invention. The semiconductor laser of the third embodiment is also a ridge type semiconductor laser according to the second aspect of the present invention. The nitride semiconductor laser 10B according to the third embodiment is a blue light emitting laser having a ridge structure and an SCH structure. As shown in FIG. 9, in the nitride-based semiconductor laser 10B according to the third embodiment, a semiconductor substrate 40 made of GaN is used, and is directly bonded onto the Ga surface, which is one main surface, so as to be n-type. A buffer layer 41 is formed. The n-type buffer layer 41 is disposed in order to reduce surface irregularities on the GaN semiconductor substrate 40 and to laminate the upper layer as flat as possible.

  On the n-type buffer layer 41, an n-type first cladding layer 42, an n-side light guide layer 43, an active layer 44 having a multiple quantum well structure, a p-type electron barrier layer 45, and a p-side light guide layer. 46, a p-type cladding layer 47, and a p-type contact layer 48 are sequentially stacked. The n-type buffer layer 41 is specifically made of n-type GaN and has a thickness of 0 to 10 μm, specifically 1 μm, for example, and is doped with silicon Si as an n-type impurity. .

The n-type first cladding layer 42 is formed by directly joining the n-type buffer layer 41, and specifically, Al _x1 Ga _y1 In _1-x1-y1 N (0 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 1). The Al composition ratio x1 of the first cladding layer 42 is 0.05 to 0.20, specifically, for example, 0.10. Further, the Ga composition ratio y1 of the first cladding layer 42 is set to 0.80 to 0.95, specifically, for example, 0.90. When the Al composition ratio x1 of the first cladding layer 42 is 0.10 and the Ga composition ratio y1 is 0.90, the In composition ratio is 0, and the first cladding layer 42 is made of AlGaN. The thickness of the first cladding layer 42 is 0.5 to 4.0 μm, specifically 1.0 μm, for example, and, for example, silicon Si is doped as the n-type impurity. The n-side light guide layer 43 is formed by directly joining the first cladding layer 42, and specifically, is composed of n-type GaN.

The active layer 44 having a multiple quantum well structure is formed by being directly joined to the n-side light guide layer 43, and is specifically composed of In _z1 Ga _{1 -z1} N / In _z2 Ga _{1 -z2} N. . The active layer 44 is formed by alternately laminating In _z1 Ga _{1 -z1} N layers as barrier layers and In _z2 Ga _{1 -z2} N layers as well layers. The In _z1 Ga _{1 -z1} N layer has a thickness of 7 nm and an In composition ratio z1 = 0.02, and the In _z2 Ga _{1 -z2} N layer as the well layer has a thickness of 3.5 nm. Therefore, the In composition ratio z2 = 0.14, and the number of wells is 3. The active layer 44 may be either a case where there are well layers at both ends or a case where there is a barrier layer.

  The p-type electron barrier layer 45 is formed by directly joining on the active layer 44, and is specifically made of AlGaN. The electron barrier layer 45 has a thickness of 0 to 40 nm, specifically 10 nm, for example, and its Al composition ratio is 0 to 0.3, specifically 0.18, for example. The p-side light guide layer 46 is formed by directly joining the electron barrier layer 45, and is specifically made of p-type GaN. The p-side light guide layer 46 has a thickness of 50 to 200 nm, specifically, for example, 100 nm.

The p-type cladding layer 47 includes a p-type second cladding layer 471, a p-type third cladding layer 472, and an etching stopper layer 473 sandwiched between the second and third cladding layers 471 and 472. Consists of two layers. The second cladding layer 471 is formed by directly joining the p-side light guide layer 46. Specifically, the second and third cladding layers 471 and 472 are both composed of Al _x2 Ga _y2 In _1-x2-y2 N (0 ≦ x2 ≦ 1, 0 ≦ y2 ≦ 1). The Al composition ratio x2 of the second and third cladding layers 471 and 472 is 0.05 to 0.20, specifically, for example, 0.07. The Ga composition ratio y2 of the second and third cladding layers 471 and 472 is 0.80 to 0.95, specifically, for example, 0.93. When the Al composition ratio x2 of the second and third cladding layers 471 and 472 is 0.07 and the Ga composition ratio y2 is 0.93, the In composition ratio is 0, and the second and third cladding layers 471, 472, Both 472 are made of AlGaN. The second cladding layer 471 has a thickness of 50 to 500 nm, for example, 100 nm, and is doped with, for example, Mg as a p-type impurity. The third cladding layer 472 is formed by directly joining the etching stopper layer 473, has a thickness of 200 nm to 4 μm, specifically 400 nm, and is doped with, for example, Mg as a p-type impurity.

The etching stopper layer 473 is formed by directly joining the second cladding layer 471. Specifically, the etching stopper layer 473 is formed of Al _x3 Ga _y3 In _1-x3-y3 N (0 ≦ x3 ≦ 1, 0 ≦ y3 ≦ 1). Composed. The Al composition ratio x3 of the etching stopper layer 473 is made larger than the Al composition ratio x2 of the second and third cladding layers 471 and 472. Specifically, the Al composition ratio x3 of the etching stopper layer 473 is 0.06 to 0.30, specifically, for example, 0.10. Further, the Ga composition ratio y3 of the etching stopper layer 473 is 0.70 to 0.94, specifically, for example, 0.90. When the Al composition ratio x3 of the etching stopper layer 473 is 0.10 and the Ga composition ratio y3 is 0.90, the In composition ratio is 0, and the etching stopper layer 473 is made of AlGaN. The etching stopper layer 473 has a thickness of 2.0 nm to 40 nm, specifically 10 nm, for example, and the p-type impurity may be either doped or undoped. Further, the Al composition ratio x3 of the etching stopper layer 473 is made larger than the Al composition ratio x2 of the second and third cladding layers, and the refractive index of the etching stopper layer 473 is set to the refraction of the second and third cladding layers 471 and 472. The etching stopper layer 473 may be made of AlGaInN other than AlGaN or other GaN-based semiconductors if the ratio is smaller than the rate.

  The p-type contact layer 48 is formed by directly bonding on the third cladding layer 472, and is specifically composed of p-type GaN. The contact layer 48 has a thickness of 50 to 500 nm, specifically 100 nm, for example, and is doped with Mg as a p-type impurity.

  In the contact layer 48, the third cladding layer 472, and the etching stopper layer 473, the ridge 15 is formed by etching in the <1-100> direction, for example, as in the first and second embodiments. The width of the ridge 15 is 1 to 5 μm, and specifically, for example, 2.2 μm. The ridge 15 is formed in a low defect region between high dislocation regions having a width of several μm to several tens of μm formed in a stripe shape on the GaN semiconductor substrate 40.

In order to protect the surface of the side surface of the ridge 15 or the lateral bottom surface of the ridge 16 and to electrically insulate, an insulating film 27 such as a SiO ₂ film having a thickness of 200 nm is formed on both sides of the ridge 15 and the grooves 16. 17 is formed so as to cover 17. An opening 27 a is provided in the insulating film 27 on the ridge 15, and electrical contact between the p-side electrode 28 and the p-type contact layer 48 is achieved through the opening 27 a. The p-side electrode 28 has a structure in which, for example, Pd and Au films are sequentially stacked. An n-side electrode 29 is formed on the N surface, which is the bottom surface opposite to the Ga surface, which is one main surface of the GaN semiconductor substrate 40. The n-type electrode 29 has a structure in which, for example, Ti and Au films are sequentially stacked.

  Next, a method for manufacturing the nitride semiconductor laser according to the third embodiment will be described. First, an n-type buffer layer 41 is grown on a GaN semiconductor substrate 40 whose surface is previously cleaned by thermal cleaning or the like by a metal organic chemical vapor deposition (MOCVD) method at a growth temperature of 1000 ° C., for example. Similarly, by the MOCVD method, the n-type first cladding layer 42, the n-side light guide layer 43, the multi-quantum well structure active layer 44, the p-type electron barrier layer 45, the p-side light guide layer 46, the p-type light guide layer 46, A second cladding layer 471, an etching stopper layer 473, a p-type third cladding layer 472, and a p-type contact layer 48 are sequentially stacked. Here, the growth temperatures of these layers are, for example, 1000 ° C. for the first cladding layer 42 and the n-side light guide layer 43, 740 ° C. for the active layer 44, and from the electron barrier layer 45 to the contact layer 48. Each layer is set to 1000 ° C.

  A resist is applied to the entire surface of the wafer on which the above crystal growth has been completed, and a resist pattern having a predetermined shape corresponding to the shape of the grooves 16 and 17 is formed by lithography. Using this resist pattern as a mask, the p-type third cladding layer 472 and the etching stopper layer 473 are etched by, eg, RIE. By this etching, a ridge 15 having an optical waveguide structure is produced. As this RIE etching gas, for example, a chlorine-based gas is used. This etching process includes a first etching process for performing dry etching and a second etching process for performing wet etching thereafter.

  In the first etching step, dry etching is performed up to the top, inside, or bottom of the etching stopper layer 473. Further, if necessary, a part of the second cladding layer 471 can be etched. In the second etching step, following the first etching step, the etching stop layer 473 is removed by wet etching as a final etching. If necessary, even a part of the second cladding layer 471 can be etched. The dry etching in the first etching step has little side etching and is effective for making the side surface of the ridge 15 a substantially vertical side surface. The wet etching in the second etching step is effective for removing damage on the etched surface due to the dry etching in the first etching step.

The etching thickness in the first etching step is monitored and controlled by irradiating laser light from the laser device. Specifically, the upper end of the semiconductor laser is irradiated with laser light from a laser device, and the end point of etching is detected by the difference in intensity of reflected light of, for example, Al from the third cladding layer 472 and the etching stop layer 473. . The dry etching in the first etching process is performed, for example, using an ICP plasma etching apparatus, using SiCl ₄ / Ar gas as an etching gas, and a pressure of about 0.5 Pa.

After the first etching step is completed, the semiconductor laser being manufactured is immersed in a wet etching solution, and the second etching step for the third cladding layer 472 is performed. For example, hydrofluoric acid is used as the wet etching solution. Following the etching process, the SiO ₂ film 27 having a thickness of, for example, 0.2 μm is formed on the entire upper surface of the substrate 40 again by using, for example, a CVD method, a vacuum evaporation method, a sputtering method, or the like while leaving the resist pattern used as a mask. Forming and removing the resist and simultaneously removing the SiO ₂ film on the ridge, so-called lift-off is performed. Thereby, the opening 27a on the ridge is formed.

  Next, after sequentially forming, for example, a vacuum deposition method on the entire upper surface of the substrate 40, a p-side electrode 28 on the upper surface is formed by resist coating, lithography, and wet etching or dry etching. Thereafter, Ti and Al films are sequentially formed on the entire bottom surface of the substrate 40 by a vacuum deposition method, and then an alloy process for bringing the n-side electrode 29 into ohmic contact is performed. Thereafter, the substrate 40 is processed into a bar shape by cleaving or the like to form both resonator end faces, and further, end faces are coated on the end faces of the resonators, and then the bar is chipped by cleaving or the like. As described above, the nitride-based semiconductor laser 10B according to the third embodiment using the present invention is manufactured.

  FIG. 10 is a graph showing the refractive index and light output distribution of the semiconductor laser according to the third embodiment. The vertical axis of FIG. 10A shows the refractive index distribution, and the vertical axis of FIG. 10B shows the light output distribution. 10A and 10B, the horizontal axis indicates the position in the thickness direction of the semiconductor laser 10B. In FIG. 10A, reference numerals 50 to 58 and 571 to 573 indicate the refractive indexes of the respective layers in the semiconductor laser 10B of the third embodiment. Reference numerals 50 to 58 denote the refractive indexes of the semiconductor substrate 40 to the contact layer 48, and reference numerals 571 to 573 denote the refractive indexes of the layers 471 to 473. FIG. 10B shows the light output distribution of the semiconductor laser 10B of the third embodiment corresponding to the refractive index of FIG.

  In the third embodiment, although the etching stopper layer 473 is used as in the second embodiment, the Al composition ratio x3 is larger than the Al composition ratio x2 of the second and third cladding layers 471 and 472. Therefore, the light output distribution of FIG. 10A is a gentle curve having a peak at a portion corresponding to the active layer 44 and being almost symmetrical on both sides of this peak. On the left side of the peak corresponding to the active layer 44, the Al composition ratio x3 of the etching stopper layer 473 is as large as 0.10, and the refractive index of the etching stopper layer 471 is small. A nearly symmetrical light output distribution is obtained.

  11 (a) and 11 (b) show the refractive index and light output distribution of the conventional blue semiconductor laser in the same manner as FIGS. 10 (a) and 10 (b) for comparison with FIGS. 10 (a) and 10 (b). It is a graph which shows. Since the conventional semiconductor laser does not have the etching stop layer 473 having a small refractive index, the light output distribution is biased toward the p-type cladding layer 47 having a large free carrier absorption as compared with the third embodiment. For this reason, the light emission efficiency is lowered and the light emission characteristics are deteriorated.

  In the third embodiment, since the layers 41 to 48 are stacked and crystal-grown on the semiconductor substrate 40, the layers 41 to 48 can be formed in a single crystal growth step, thereby improving productivity. be able to.

  In the third embodiment, the end point of etching is detected based on the difference in reflected light intensity of Al from the third cladding layer 472 and the etching stopper layer 473. However, based on the interference between the incident light from the laser device and the reflected light from the active layer 44 or the reflected light from the semiconductor substrate 40, the etching thickness of the third cladding layer 472 by dry etching in the first etching step is reduced. It is also possible to measure and determine the end point of etching from the remaining thickness from the original thickness. According to this etching end detection method, the end point of etching can be accurately determined even when the etching stop layer 473 is not present as in the first embodiment.

  The present invention can be applied to a semiconductor laser having a ridge, for example, a ridge type semiconductor laser or a ridge buried type semiconductor laser.

FIG. 1 is a perspective view showing a semiconductor laser according to a first embodiment of the present invention, with a part cut. 2 is a cross-sectional view taken along line AA in FIG. FIG. 3 is a graph showing the refractive index and light output distribution of the first embodiment. FIG. 4 is a graph showing the refractive index and light output distribution of a conventional semiconductor laser. FIG. 5 is a graph showing the light output characteristics of the first embodiment. FIG. 6 is a perspective view showing a second embodiment of the semiconductor laser according to the present invention, with a part cut. FIG. 7 is a sectional view taken along line BB in FIG. FIG. 8 is a graph showing the refractive index and light output distribution of the second embodiment. FIG. 9 is a sectional view of the central portion including the ridge according to the third embodiment of the semiconductor laser according to the present invention. FIG. 10 is a graph showing the refractive index and light output distribution of the third embodiment. FIG. 11 is a graph showing the refractive index and light output distribution of a conventional semiconductor laser.

Explanation of symbols

10, 10A, 10B: semiconductor laser, 11, 12: end face, 15: ridge,
16, 17: groove,
20, 40: semiconductor substrate, 21, 42: first cladding layer, 22, 44: active layer,
23, 471: second cladding layer, 24, 472: third cladding layer,
234, 473: Etching stopper layers.

Claims (14)

  A first conductivity type first cladding layer formed on a first conductivity type semiconductor substrate, an active layer formed on the first cladding layer, and a second conductivity type formed on the active layer. A semiconductor laser having a second cladding layer and a third cladding layer of a second conductivity type formed on the second cladding layer, wherein at least a ridge is formed on the third cladding layer, 3. A semiconductor laser characterized in that three cladding layers are formed by directly bonding on the second cladding layer.   2. The semiconductor laser according to claim 1, wherein the ridge is formed by a groove penetrating the third cladding layer.   2. The semiconductor laser according to claim 1, wherein the ridge is formed by a groove extending from the third cladding layer to a surface portion of the second cladding layer.   2. The semiconductor laser according to claim 1, wherein the first cladding layer is made of n-type AlGaInP, and the second and third cladding layers are made of p-type AlGaInP.   A first conductivity type first cladding layer formed on the first conductivity type semiconductor substrate, an active layer formed on the first cladding layer, and a second layer containing Al formed on the active layer. A conductive second cladding layer; an Al-containing etching stopper layer formed on the second cladding layer; and a second conductive-type third cladding layer containing Al formed on the etching stopper layer. A semiconductor laser having a ridge formed in the third cladding layer, wherein an Al composition ratio of the etching stopper layer is larger than an Al composition ratio of the third cladding layer.   6. The semiconductor laser according to claim 5, wherein the first cladding layer is made of n-type AlGaInP, and the second and third cladding layers are made of p-type AlGaInP. 6. The semiconductor laser according to claim 5, wherein the first cladding layer is composed of n-type Al _x1 Ga _y1 In _1-x1-y1 N (0 ≦ x1 ≦ 1, 0 ≦ y1 ≦ 1). 2. A semiconductor laser characterized in that the third cladding layer is made of p-type Al _x2 Ga _y2 In _1-x2-y2 N (0 ≦ x2 ≦ 1, 0 ≦ y2 ≦ 1).   A first conductivity type first cladding layer formed on a first conductivity type semiconductor substrate, an active layer formed on the first cladding layer, and a second conductivity type formed on the active layer. Manufacturing of a semiconductor laser having a second cladding layer and a third cladding layer of a second conductivity type formed by direct bonding on the second cladding layer, and at least a ridge formed in the third cladding layer The method includes an etching step of forming the ridge, which includes a first etching step of dry etching the third cladding layer to a predetermined thickness, and the third etching step after the first etching step. A method of manufacturing a semiconductor laser, comprising a second etching step of wet-etching the cladding layer.   A first conductivity type first cladding layer formed on the first conductivity type semiconductor substrate, an active layer formed on the first cladding layer, and a second layer containing Al formed on the active layer. Conductive p-type second cladding layer, an etching stopper layer containing Al formed on the second cladding layer, and a second conductive type third cladding layer containing Al formed on the etching stopper layer A semiconductor laser manufacturing method in which an Al composition ratio of the etching stopper layer is larger than an Al composition ratio of the third cladding layer, and a ridge is formed in the third cladding layer, An etching process to be formed. The etching process includes a first etching process for dry-etching the third cladding layer to a predetermined thickness, and the etching stop after the first etching process. The semiconductor laser manufacturing method, characterized in that the third cladding layer comprising a second etching step of wet-etching until the layer is exposed.   10. The method of manufacturing a semiconductor laser according to claim 8, wherein in the first etching step, irradiation laser light is applied toward the third cladding layer of the semiconductor laser, incident light of the irradiation laser light, and the semiconductor A method of manufacturing a semiconductor laser, comprising controlling the etching thickness by the dry etching based on interference with reflected light from the inside of the laser.   11. The method of manufacturing a semiconductor laser according to claim 10, wherein in the first etching step, an etching thickness by the dry etching is controlled based on interference between the incident light and a reflected laser light from the active layer. A method of manufacturing a semiconductor laser.   11. The method of manufacturing a semiconductor laser according to claim 10, wherein in the first etching step, an etching thickness by the dry etching is controlled based on interference between the incident light and reflected laser light from the semiconductor substrate. A method of manufacturing a semiconductor laser.   9. The method of manufacturing a semiconductor laser according to claim 8, wherein in the first etching step, an irradiation laser beam is applied toward the third cladding layer of the semiconductor laser, and the second cladding layer and the second cladding layer with respect to the irradiation laser beam. 3. A method for manufacturing a semiconductor laser, comprising: controlling an etching thickness by dry etching based on a difference in reflectance from the three cladding layers.   10. The method of manufacturing a semiconductor laser according to claim 9, wherein in the first etching step, irradiation laser light is applied toward the third cladding layer of the semiconductor laser, and the etching stopper layer and the third for the irradiation laser light are provided. A method of manufacturing a semiconductor laser, comprising: controlling an etching thickness by dry etching based on a difference in reflectance from a cladding layer.

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