JP2006074010A - Semiconductor laser and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a semiconductor laser of high output and high reliability by preventing impurities diffused from a cladding layer by a heat treatment process and energization, etc. from being further diffused in an active layer. <P>SOLUTION: A double heterojunction structure part, including an n-GaAs buffer layer 102, n-(Al<SB>0.7</SB>Ga<SB>0.3</SB>)<SB>0.5</SB>In<SB>0.5</SB>P cladding layer 103 (Si doping), an active layer 104 (Si doping), and a first p-(Al<SB>0.7</SB>Ga<SB>0.3</SB>)<SB>0.5</SB>In<SB>0.5</SB>P cladding layer 105 (Zn doping) overlaied in this order on an n-GaAs substrate 101, is formed. The active layer 104 is constituted by four Ga<SB>0.5</SB>In<SB>0.5</SB>P well layers 202A-202D (Si doping), three (Al<SB>0.5</SB>Ga<SB>0.5</SB>)<SB>0.5</SB>In<SB>0.5</SB>P barrier layers 203A-203C (Si doping) among the layers 202A-202D, and (Al<SB>0.5</SB>Ga<SB>0.5</SB>)<SB>0.5</SB>In<SB>0.5</SB>P optical guide layer 201 and 204 (Si doping) formed so as to sandwich them. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a semiconductor laser, and more particularly to a structure of a semiconductor laser capable of suppressing the movement of impurities diffused in an active layer region and a method for manufacturing the same.

  A semiconductor laser using an AlGaInP-based compound semiconductor is widely used as a light source for pick-up of an optical disk apparatus for processing a DVD or the like as a red laser having an oscillation wavelength of 650 nm.

  In addition to red semiconductor lasers used for DVDs, infrared semiconductor lasers having a 780 nm band emission wavelength used for CDs, CD-Rs, etc. can be used as cladding layers from the viewpoint of higher output and integration with red lasers. AlGaInP-based materials are used.

  In recent years, a high-power stable operation of a red semiconductor laser of 200 mW or more is required for a rewritable optical disk, and it is an essential condition to dope a p-type cladding layer with a high concentration of impurities.

  In the case where impurities are doped at a high concentration in the clad layer using an AlGaInP-based material, there is a problem that the impurities are easily diffused into the non-doped active layer during energization or a thermal process, and the laser characteristics are likely to be deteriorated.

  As conventional solutions, in order to suppress diffusion of impurities into the active layer, it has been generally performed to reduce the impurity concentration or provide an undoped region in the cladding layer near the interface with the active layer. It was. In addition, a highly reliable semiconductor laser can be obtained by simultaneously doping the clad layer with one main conductivity type impurity and a small amount of opposite conductivity type impurities at the same time, and attracting each other, thereby making it difficult for the main impurity alone to diffuse. I have made it.

As an example of manufacturing a highly reliable semiconductor laser by the above-described simultaneous doping, for example, a structure and a manufacturing method as disclosed in Patent Documents 1 to 3 have been proposed.
JP-A-4-249391 Japanese Patent Laid-Open No. 5-175607 JP-A-9-219567

  In the above prior art, a small amount of p-type impurity is co-doped in the n-type cladding layer, or a small amount of n-type impurity is simultaneously doped in the p-type cladding layer, or a small amount of p-type impurity in the n-type cladding layer. And the p-type cladding layer are doped with a small amount of n-type impurities at the same time, thereby suppressing the diffusion of impurities into the active layer.

  However, even if these methods are used, when impurities are diffused into the active layer, the problem that impurities diffused during a long high-power operation induce defects and easily cause laser degradation cannot be solved.

  Therefore, the present invention suppresses further diffusion of impurities diffused from the clad layer by a thermal process or energization in the active layer, and p-type impurities diffuse from the p-type clad layer, which is a particular problem, to the active layer. An object of the present invention is to provide a semiconductor laser that can obtain high output and highly reliable laser characteristics.

  In order to solve the above problems, a semiconductor laser according to the present invention includes a first conductive clad layer and a second conductive clad layer, a first conductive clad layer, and a second conductive clad layer on a semiconductor substrate. And an active layer located between the active layers, wherein the active layer contains impurities.

  The active layer may include a quantum well or a single light emitting layer, a barrier layer, and a light guide region.

  The impurity in the active layer is an impurity of a conductivity type opposite to the impurity in the first conductivity type cladding layer, and the impurity in the first conductivity type cladding layer is in the first conductivity type cladding layer or the active layer. In the layer, a substance having a larger diffusion coefficient than the impurity in the active layer is preferable.

  Alternatively, the impurity in the active layer is an impurity having a conductivity type opposite to the impurity in the second conductivity type cladding layer, and the impurity in the second conductivity type cladding layer is in the second conductivity type cladding layer or The active layer is preferably a substance having a diffusion coefficient larger than that of the impurities in the active layer.

  Alternatively, the active layer contains an impurity having a conductivity type opposite to the impurity in the first conductivity type cladding layer and an impurity having a conductivity type opposite to the impurity in the second conductivity type cladding layer. The impurity in the one conductivity type cladding layer is a substance having a diffusion coefficient larger than that of the second conductivity type impurity in the active layer in the first conductivity type cladding layer or in the active layer. The impurity in the type cladding layer is preferably a substance having a diffusion coefficient larger than that of the first conductivity type impurity in the active layer in the second conductivity type cladding layer or in the active layer.

The concentration of impurities in the active layer is more preferably in the range of 1 × 10 ¹⁶ cm ^{−3 to} 3 × 10 ¹⁷ cm ⁻³ in total.

  More preferably, one or both of the first conductivity type cladding layer and the second conductivity type cladding layer is co-doped with an impurity having a conductivity type opposite to the impurity in each cladding layer.

  Of the impurities in the active layer, the impurity having the first conductivity type is preferably one of Si, S, and Te.

  Of the impurities in the active layer, the impurity having the second conductivity type is preferably one of Mg, C, Be, and Cd.

The active layer is preferably made of at least an AlGaInP-based material.
The first conductivity type cladding layer and the second conductivity type cladding layer are preferably made of at least an AlGaInP-based material.

  The semiconductor laser manufacturing method of the present invention includes a first step of forming a first conductivity type cladding layer while adding a first conductivity type impurity on a semiconductor substrate, and an active layer on the first conductivity type cladding layer. A semiconductor laser manufacturing method comprising: a second step of forming a second conductive type cladding layer while adding a second conductive type impurity on the active layer; The second step is characterized in that the active layer is formed while adding impurities.

In the second step, the active layer having a multilayer structure may be formed.
In the second step, the active layer is formed while adding an impurity having a conductivity type opposite to the impurity in the first conductivity type cladding layer, and the impurity in the first conductivity type cladding layer is converted into the first conductivity type. In the clad layer or in the active layer, a material having a diffusion coefficient larger than that of impurities in the active layer is preferable.

  Alternatively, in the second step, the active layer is formed while adding an impurity of a conductivity type opposite to the impurity in the second conductivity type cladding layer, and the impurity in the second conductivity type cladding layer is In the conductive clad layer or in the active layer, a material having a diffusion coefficient larger than that of impurities in the active layer is preferable.

  Alternatively, in the second step, the active layer is added while adding an impurity having a conductivity type opposite to the impurity in the first conductivity type cladding layer and an impurity having a conductivity type opposite to the impurity in the second conductivity type cladding layer. And the impurity in the first conductivity type cladding layer is a substance having a larger diffusion coefficient than the second conductivity type impurity in the active layer in the first conductivity type cladding layer or in the active layer. And the impurity in the second conductivity type cladding layer is a substance having a larger diffusion coefficient in the second conductivity type cladding layer or in the active layer than the impurity of the first conductivity type in the active layer. Is preferred.

In the second step, it is more preferable to form the active layer so that the total concentration of impurities in the active layer is in the range of 1 × 10 ¹⁶ cm ^{−3 to} 3 × 10 ¹⁷ cm ⁻³ .

  In one or both of the first step and the third step, one or both of the first conductivity type cladding layer and the second conductivity type cladding layer are obtained by co-doping an impurity having a conductivity type opposite to the impurity in each cladding layer. It is more preferable to form

  Preferably, the method further includes a step of diffusing impurities in the vicinity of the cavity end face of the semiconductor laser to form a window structure.

  Alternatively, at one or both of the interface between the active layer and the first conductivity type cladding layer and the interface between the active layer and the second conductivity type cladding layer, an impurity having a conductivity type opposite to the impurity in each cladding layer is delta-doped. More preferably.

  Alternatively, the interface between the first conductivity type cladding layer formed in the first step and the active layer formed in the second step, and the interface between the active layer formed in the second step and the third step More preferably, at the interface of the second conductivity type cladding layer, the impurities in each cladding layer and the impurities of the anticonductivity type are delta-doped.

  According to the present invention, it is possible to suppress the diffusion of impurities diffused into the active layer due to the thermal process during manufacturing, and because it attracts each other with the opposite conductivity type impurities, it is difficult for the impurities alone to move. Can provide a high-performance semiconductor laser.

(Embodiment 1)
Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  1 is a cross-sectional view of the semiconductor laser according to the first embodiment of the present invention viewed from the cavity end face direction, FIG. 2 is a cross-sectional view of the same semiconductor laser viewed from the cavity length direction, and FIG. It is a laminated structure figure of the active layer of a laser.

The semiconductor laser according to the first embodiment shown in FIGS. 1 to 3 has the following structure.
An n-GaAs buffer layer 102 (Si-doped, dopant concentration: 1.0 × 10 ¹⁸ cm ⁻³ ) on an n-GaAs substrate 101 (Si-doped, 1.0 × 10 ¹⁸ cm ⁻³ ). 0.5 μm is formed. The buffer layer 102 is necessary for improving the crystallinity of the cladding layers 103, 105, 107, the active layer 104, and the like described below.

On the n-GaAs buffer layer 102, an n- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer 103 (Si-doped, 1.2 × 10 ¹⁸ cm ⁻³ ) 2.0 μm, an active layer 104 (Si-doped) 92 nm, first p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer 105 (Zn-doped, 5 × 10 ¹⁷ cm ⁻³ ) 175 nm, p-Ga _0.5 In _0.5 P etching stop layer 106 (Zn-doped, 1 × 10 ¹⁸ cm ⁻³ ) 10 nm, second p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P clad layer 107 (Zn-doped, 1.1 × 10 ¹⁸ cm ⁻³ ) 1.0 μm, p-Ga _0.5 In _A double heterojunction structure having a _0.5 P cap layer 108 (Zn-doped, 1 × 10 ¹⁸ cm ⁻³ ) 50 nm is formed.

  The composition of each of the above layers is an example, and the lattice constants of the double heterojunction layers 103 to 107 and the cap layer 108 are substantially equal to those of the n-GaAs substrate 101, and the cladding layers 103, 105, and 107, and the etching stop layer 106 are included. The composition of In, Ga, and Al is determined so that the band gap energy of the cap layer 108 is larger than the band gap energy of the active layer 104.

An n-Al _0.5 In _0.5 P current blocking layer 109 (Si-doped, 5.0 × 10 ¹⁷ cm ⁻³ ) 300 nm is formed on the ridge side portion of the second p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer 107. The p-GaAs cap layer 110 (Zn-doped, 5 × 18 ¹⁸ cm ⁻³ ) 3 is formed on the p-Ga _0.5 In _0.5 P cap layer 108 and the n-Al _0.5 In _0.5 P current blocking layer 109. 0.0 μm is formed. A p-side electrode 112 is formed on the upper surface of the p-GaAs cap layer 110, and an n-side electrode 111 is formed on the lower surface of the n-GaAs substrate 101. Note that all layers except the p-side electrode 112 and the n-side electrode 111 are formed by crystal growth by the metal organic chemical vapor deposition layer method (MOCVD method), and impurities in each layer are generated when each layer is crystal-grown. It is added at the same time.

  In the above-described semiconductor laser, window regions 113 and 114 are formed in a region which becomes a cavity end face of the laser as shown in FIG. After the double heterojunction structure is formed, the window regions 113 and 114 are formed by thermal diffusion of Zn from the surface at about 600 ° C. for 90 minutes.

  The quantum well structure of the active layer 104 is disordered by Zn diffusion, and window regions 113 and 114 having an increased band gap are formed, thereby suppressing end face optical damage (COD; Catastrophic Optical Damage) due to high power operation and surge voltage. be able to.

The active layer 104 is a strained quantum well active layer as shown in FIG. 3, and four Ga _0.5 In _0.5 P well layers 202A to 202D (Si-doped, 1.0 × 10 ¹⁷ cm ⁻³ ) have a thickness of 5 nm. The three (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P barrier layers 203A to 203C (Si-doped, 1.0 × 10 ¹⁷ cm ⁻³ ) thickness 5 nm between these layers are formed so as to sandwich them. (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P light guide layers 201 and 204 (Si-doped, 1.0 × 10 ¹⁷ cm ⁻³ ) with a thickness of 28 nm.

Here, the operation of the semiconductor laser in the first embodiment will be specifically described.
The P-type cladding layers 105 and 107 are doped with Zn as a p-type impurity. It is well known that Zn diffuses easily in AlGaInP-based materials. Zn diffuses into the active layer 104 by a thermal process or energization when the window regions 113 and 114 are formed, and the reliability of the laser is improved by inducing defects due to impurity diffusion. Hurt.

  In this embodiment, even if Zn diffuses into the active layer 104, the active layer 104 is doped with Si in advance so that the movement of Zn can be suppressed. FIG. 4 is a schematic diagram showing a state of impurity diffusion from the cladding layer 105 to the active layer 104 in the present embodiment.

  As shown in FIG. 4, if Si, which is an impurity having a conductivity opposite to that of Zn as an impurity in the clad layer 105, is present in the active layer 104 in advance, Zn diffused in the active layer 104 and the active layer 104 are doped. Since the attracted Si attracts each other by ionic bonding or the like, the movement of Zn in the active layer 104 can be suppressed even during a heat treatment step such as crystal growth or a window structure forming step or during energization. Further, since Zn and Si attract each other, it is difficult to form deep impurity levels in the active layer 104, so that a highly reliable semiconductor laser with a low threshold current can be realized.

Note that Si doped in the active layer 104 is preferably kept at a low concentration within a necessary limit so as not to form deep impurity levels at high density by itself, and is preferably 1 × 10 ¹⁶ cm ^{−3 to} 3 × 10 6. If it is in the range of ¹⁷ cm ⁻³ , the suppression of impurity diffusion and the suppression of deep impurity level formation can both be achieved. The concentration of impurities is more preferably in the range of 1 × 10 ¹⁶ cm ^{−3 to} 3 × 10 ¹⁷ cm ⁻³ in total.

  Further, in the present embodiment, the case where the impurity of the P-type cladding layer is Zn is shown, but the same effect as described above can be obtained even when C, Be, Cd, or the like is used instead of Zn. is there.

  In the present embodiment, the entire active layer 104, that is, the light guide layers 201 and 204, the well layers 202A to 202D, and the barrier layer 203 are doped with Si. The amount of p-type impurities diffused into the active layer 104 varies depending on the adjustment of the amount of impurities doped into the cladding layer. When this amount is small, it is possible to sufficiently suppress the diffusion of the p-type impurity in the active layer 104 by doping part of the active layer 104 with Si. For example, Si may be doped only in the light guide layer 204, Si may be doped from the light guide layer 204 to the well layer 202C, or Si may be doped from the light guide layer 204 to the well layer 202A.

(Embodiment 2)
Next, the second embodiment of the present invention will be described. The laminated structure is the same as that of the first embodiment, and the main difference is that Se is doped as an impurity into the n-type cladding layer, and Mg is doped as an impurity into the active layer. Since it is used, its structure will be briefly described with reference to FIGS.

An n-GaAs buffer layer 102 (Se doped, 1.2 × 10 ¹⁸ cm ⁻³ ), 0.5 μm is formed on the n-GaAs substrate 101 (Si doped, 1.0 × 10 ¹⁸ cm ⁻³ ). . The buffer layer 102 is necessary for improving the crystallinity of the cladding layers 103, 105, 107, the active layer 104, and the like described below.

On the n-GaAs buffer layer 102, an n- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer 103 (Se doped, 1.2 × 10 ¹⁸ cm ⁻³ ) 2.0 μm, an active layer 104 (Mg doped) 92 nm, first p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer 105 (Zn doped, 5 × 10 ¹⁷ cm ⁻³ ) 175 nm, p-Ga _0.5 In _0.5 P etching stop layer 106 (Zn doped, 1 × 10 ¹⁸ cm ⁻³ ) 10 nm, second p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P clad layer 107 (Zn-doped, 1.1 × 10 ¹⁸ cm ⁻³ ) 1.0 μm, p-Ga _0.5 In _A double heterojunction structure having a _0.5 P cap layer 108 (Zn-doped, 1 × 10 ¹⁸ cm ⁻³ ) 50 nm is formed.

  The composition of each of the above layers is an example, and the lattice constants of the double heterojunction layers 103 to 107 and the cap layer 108 are substantially equal to those of the n-GaAs substrate 101, and the cladding layers 103, 105, and 107, and the etching stop layer 106 are included. The composition of In, Ga, and Al is determined so that the band gap energy of the cap layer 108 is larger than the band gap energy of the active layer 104.

On the side of the second p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer 107 is an n-Al _0.5 In _0.5 P current blocking layer 109 (Se doped, 5.0 × 10 ¹⁷ cm ⁻³ ) 300 nm. 2. A p-GaAs cap layer 110 (Zn-doped, 5 × 18 ¹⁸ cm ⁻³ ) is formed on the p-Ga _0.5 In _0.5 P cap layer 108 and the n-Al _0.5 In _0.5 P current blocking layer 109. 0 μm is formed. A p-side electrode 112 is formed on the upper surface of the p-GaAs cap layer 110, and an n-side electrode 111 is formed on the lower surface of the n-GaAs substrate 101. All layers except the p-side electrode 112 and the n-side electrode 111 are formed by crystal growth by the metal organic chemical vapor deposition layer method (MOCVD method).

Here, the manufacturing method of the window regions 113 and 114 is the same as that of the first embodiment.
The active layer 104 is a strained quantum well active layer, and four Ga _0.5 In _0.5 P well layers 202 (Mg-doped, 1.0 × 10 ¹⁷ cm ⁻³ ) have a thickness of 5 nm and three layers between these layers. (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P barrier layer 203 (Mg-doped, 1.0 × 10 ¹⁷ cm ⁻³ ) 5 nm thick and (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P light guide layer 201 sandwiching them 204 (Mg-doped, 1.0 × 10 ¹⁷ cm ⁻³ ) with a thickness of 28 nm.

Here, the operation of the semiconductor laser in the second embodiment will be specifically described.
The n-type cladding layer 103 is doped with Se as an n-type impurity. Mg, which is a p-type impurity, is relatively difficult to diffuse in an AlGaInP-based material, while Se, which is an n-type impurity, is likely to diffuse.

  Therefore, Se diffuses into the active layer 104 by heat treatment processes such as crystal growth and window structure formation processes and energization, and there is a possibility that the reliability of the laser is impaired by inducing defects due to impurity diffusion. Therefore, the active layer 104 is doped in advance with Mg so that the movement of Se can be suppressed even if Se diffuses into the active layer 104.

  FIG. 5 is a schematic diagram showing a state of impurity diffusion from the cladding layer 103 to the active layer 104 in the present embodiment.

  As shown in FIG. 5, if Mg, which is an impurity having a conductivity opposite to that of Se in the cladding layer 103, is present in the active layer 104 in advance, Se diffused in the active layer 104 and the active layer 104 are doped. Since the Mg that has been attracted to each other by ionic bonding or the like, the movement of Se in the active layer 104 can be suppressed even during a thermal process or during energization. In addition, since Se and Mg attract each other, it is difficult to form deep impurity levels in the active layer 104, so that a highly reliable semiconductor laser with a low threshold current can be realized.

Note that Mg doped in the active layer 104 is preferably kept at a low concentration within a necessary limit so as not to form deep impurity levels at high density by itself, and is preferably 1 × 10 ¹⁶ cm ^{−3 to} 3 × 10 6. If it is in the range of ¹⁷ cm ⁻³ , the suppression of impurity diffusion and the suppression of deep impurity level formation can both be achieved.

  In the present embodiment, the case where the impurity of the n-type cladding layer is Se is shown. However, the same effect as described above can be obtained even when S, Te, or the like is used instead of Se.

  In the present embodiment, the entire active layer 104, that is, the light guide layers 201 and 204, the well layers 202A to 202D, and the barrier layer 203 are doped with Mg. The amount of n-type impurities diffused into the active layer 104 varies depending on the adjustment of the amount of impurities doped in the cladding layer. When this amount is small, it is possible to sufficiently suppress the diffusion of n-type impurities in the active layer 104 by doping part of the active layer 104 with Mg. For example, Mg may be doped only in the light guide layer 201, Mg may be doped from the light guide layer 201 to the well layer 202B, or Mg may be doped from the light guide layer 201 to the well layer 202D.

(Embodiment 3)
Next, the third embodiment of the present invention will be described. The laminated structure is the same as that of the first embodiment. The main difference is that Se is doped as an impurity into the n-type cladding layer, Si is doped as an impurity into the active layer. Since Mg is used, its structure will be briefly described with reference to FIGS.

An n-GaAs buffer layer 102 (Se doped, 1.0 × 10 ¹⁸ cm ⁻³ ), 0.5 μm is formed on the n-GaAs substrate 101 (Si doped, 1.0 × 10 ¹⁸ cm ⁻³ ). . The buffer layer 102 is necessary for improving the crystallinity of the cladding layers 103, 105, 107, the active layer 104, and the like described below.

On the n-GaAs buffer layer 102, an n- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer 103 (Se doped, 1.2 × 10 ¹⁸ cm ⁻³ ) 2.0 μm, an active layer 104 (Si and Mg) Doped) 92 nm, first p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer 105 (Zn doped, 5 × 10 ¹⁷ cm ⁻³ ) 175 nm, p-Ga _0.5 In _0.5 P etching stop layer 106 (Zn doped) 1 × 10 ¹⁸ cm ⁻³ ) 10 nm, second p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P clad layer 107 (Zn-doped, 1.1 × 10 ¹⁸ cm ⁻³ ) 0.9 μm, p-Ga _A double heterojunction structure portion of 50 nm of _0.5 In _0.5 P cap layer 108 (Zn-doped, 1 × 10 ¹⁸ cm ⁻³ ) is formed.

  The composition of each of the above layers is an example, and the lattice constants of the double heterojunction layers 103 to 107 and the cap layer 108 are substantially equal to those of the n-GaAs substrate 101, and the cladding layers 103, 105, and 107, and the etching stop layer 106 are included. The composition of In, Ga, and Al is determined so that the band gap energy of the cap layer 108 is larger than the band gap energy of the active layer 104.

On the side of the second p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer 107 is an n-Al _0.5 In _0.5 P current blocking layer 109 (Se doped, 5.0 × 10 ¹⁷ cm ⁻³ ) 300 nm. 2. A p-GaAs cap layer 110 (Zn-doped, 5 × 18 ¹⁸ cm ⁻³ ) is formed on the p-Ga _0.5 In _0.5 P cap layer 108 and the n-Al _0.5 In _0.5 P current blocking layer 109. 0 μm is formed. A p-side electrode 112 is formed on the upper surface of the p-GaAs cap layer 110, and an n-side electrode 111 is formed on the lower surface of the n-GaAs substrate 101. All layers except the p-side electrode 112 and the n-side electrode 111 are formed by crystal growth by the metal organic chemical vapor deposition layer method (MOCVD method).

Here, the manufacturing method of the window regions 113 and 114 is the same as that of the first embodiment.
The active layer 104 is a strained quantum well active layer, and four In _0.5 Ga _0.5 P well layers 202A and 202B (Mg doped, 1.0 × 10 ¹⁷ cm ⁻³ ), 202C and 202D (Si doped amount) 1.0 × 10 ¹⁷ cm ⁻³ ) 5 nm in thickness and three (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P barrier layers 203A (Mg-doped, 1.0 × 10 ¹⁷ cm ⁻³ ) between these layers ), 203B, 203C (Si doping amount, 1.0 × 10 ¹⁷ cm ⁻³ ) thickness 5 nm and sandwiching them (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P light guide layer 201 (Mg doping, 1.0 × 10 ¹⁷ cm ⁻³ ), 204 (Si-doped, 1.0 × 10 ¹⁷ cm ⁻³ ) and a thickness of 28 nm.

Here, the operation of the semiconductor laser in the third embodiment will be specifically described.
The n-type cladding layer 103 is doped with Se as an impurity of the n-type cladding layer. Further, Zn is used as an impurity of the p-type cladding layer. Se and Zn are likely to diffuse into the active layer 104 by heat treatment processes such as crystal growth and window structure forming processes and energization, and there is a possibility that the reliability of the laser may be impaired by inducing defects due to impurity diffusion. Therefore, Mg and Si are doped in advance in the active layer 104 so that the movement of these dopants can be suppressed even if Se and Zn diffuse into the active layer 104.

  FIG. 6 is a schematic diagram showing the state of impurity diffusion from the cladding layers 105 and 103 to the active layer 104 in the present embodiment.

  As shown in FIG. 6, Se, which is an impurity in the n-type cladding layer 103, and Mg and Si, which are impurities of the opposite conductivity type to Zn, which are impurities in the p-type cladding layer 105, are present in the active layer 104 in advance. Then, Se diffused in the active layer 104 and Mg doped in the active layer 104, and Zn diffused in the active layer 104 and Si doped in the active layer 104 are mutually connected by ionic bonds or the like. Therefore, the movement of Se and Zn in the active layer 104 can be suppressed during the heat process and during energization. In addition, since Se and Mg, Zn and Si attract each other, it is difficult to form deep impurity levels in the active layer 104, so that a highly reliable semiconductor laser with a low threshold current can be realized.

Note that Mg and Si doped in the active layer 104 are preferably kept at a low concentration within a necessary limit so as not to form deep impurity levels at a high density by themselves, and the total is 1 × 10 ¹⁶ cm ^−3. In the range of ˜3 × 10 ¹⁷ cm ⁻³ , it is possible to achieve both suppression of impurity diffusion and suppression of deep impurity level formation.

  Further, in the present embodiment, the case where the impurity of the p-type cladding layer is Zn and the impurity of the n-type cladding layer is Se is shown, but C, Be, Cd, etc. are substituted for Zn, and S is substituted for Se. Even when Te or the like is used, the same effect as described above can be obtained.

  In this embodiment, the light guide layer 201, the well layers 202A and 202B, and the barrier layer 203A are doped with Mg, and the light guide layer 204, the well layers 202C and 202D, and the barrier layers 203B and 203C are doped with Si. However, the position of each doping in the active layer 104 may be changed according to the ratio of the n-type impurity and the p-type impurity diffused in the active layer 104.

(Embodiment 4)
Next, a fourth embodiment of the present invention will be described. The laminated structure is the same as that of the first embodiment, and the main difference is that a small amount of n-type impurities are simultaneously doped (co-doped) in a part of the p-type cladding layer. In addition, since the active layer is doped with a small amount of n-type impurity, the structure will be briefly described with reference to FIGS.

An n-GaAs buffer layer 102 (Si doped, 1.0 × 10 ¹⁸ cm ⁻³ ), 0.5 μm is formed on the n-GaAs substrate 101 (Si doped, 1.0 × 10 ¹⁸ cm ⁻³ ). . The buffer layer 102 is necessary for improving the crystallinity of the cladding layers 103, 105, 107 and the active layer 104 described below.

On the n-GaAs buffer layer 102, an n- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer 103 (Si-doped, 1.2 × 10 ¹⁸ cm ⁻³ ) 2.0 μm, an active layer 104 (Si-doped) 92 nm, first p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer 105 (Zn dope: 7 × 10 ¹⁷ cm ⁻³ , Si dope: 1.0 × 10 ¹⁷ cm ⁻³ ) 175 nm, p-Ga _0.5 In _0.5 P etching stop layer 106 (Zn doping: 1 × 10 ¹⁸ cm ⁻³ , Si doping: 1.2 × 10 ¹⁷ cm ⁻³ ) 10 nm, second p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P Cladding layer 107 (Zn doping: 1.1 × 10 ¹⁸ cm ⁻³ , Si doping: 1.2 × 10 ¹⁷ cm ⁻³ ) 0.9 μm, p-Ga _0.5 In _0.5 P cap layer 108 (Zn doping, 1 × 10 ¹⁸ cm ^-3) to double consisting 50nm B joint structure section is formed.

  The composition of each of the above layers is an example, and the lattice constants of the double heterojunction layers 103 to 107 and the cap layer 108 are substantially equal to those of the n-GaAs substrate 101, and the cladding layers 103, 105, and 107, and the etching stop layer 106 are included. The composition of In, Ga, and Al is determined so that the band gap energy of the cap layer 108 is larger than the band gap energy of the active layer 104.

On the side of the second p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer 107 is an n-Al _0.5 In _0.5 P current blocking layer 109 (Si-doped, 5.0 × 10 ¹⁷ cm ⁻³ ) 300 nm. 2. A p-GaAs cap layer 110 (Zn-doped, 5 × 18 ¹⁸ cm ⁻³ ) is formed on the p-Ga _0.5 In _0.5 P cap layer 108 and the n-Al _0.5 In _0.5 P current blocking layer 109. 0 μm is formed. A p-side electrode 112 is formed on the upper surface of the p-GaAs cap layer 110, and an n-side electrode 111 is formed on the lower surface of the n-GaAs substrate 101. All layers except the p-side electrode 112 and the n-side electrode 111 are formed by crystal growth by the metal organic chemical vapor deposition layer method (MOCVD method).

Here, the manufacturing method of the window regions 113 and 114 is the same as that of the first embodiment.
Further, the active layer 104 is a strained quantum well active layer as shown in FIG. 3, and has four In _0.5 Ga _0.5 P well layers 202A to 202D (Si-doped, 1.0 × 10 ¹⁷ cm ⁻³ ) thickness. 5 nm and three (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P barrier layers 203A to 203C (Si-doped, 1.0 × 10 ¹⁷ cm ⁻³ ) thickness 5 nm between these layers and sandwich them (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P light guide layers 201 and 204 (Si-doped, 1.0 × 10 ¹⁷ cm ⁻³ ) with a thickness of 28 nm.

Here, the operation of the semiconductor laser in the fourth embodiment will be specifically described.
The p-type cladding layers 105 and 107 and the etching stop layer 106 are doped with Zn as a p-type impurity. In the present embodiment, Zn diffusion due to heat treatment processes such as crystal growth and window structure formation processes and energization is first suppressed in the cladding layer 105 and further suppressed in the active layer 104 to induce defects due to impurity diffusion. In order to reduce the resistance by increasing the impurity concentration of the p-type cladding layer in order to realize an ultra-high-power laser of 200 to tens of mW or more. It is valid.

  FIG. 7 is a schematic diagram showing a state of impurity diffusion from the cladding layer 105 to the active layer 104 in the present embodiment.

  As shown in FIG. 7, if Si, which is an impurity having a conductivity opposite to that of Zn, which is an impurity in the p-type cladding layer 105, is present in the p-type cladding layer 105 and the active layer 104 in advance, first, the p-type cladding layer Even if Zn and Si are attracted to each other in the layer 105 and diffusion of Zn is suppressed and Zn is further diffused into the active layer 104, Si doped in the active layer 104 is mutually bound by Zn and ionic bonds or the like. Therefore, the movement of Zn in the active layer 104 can be suppressed even during the thermal process or during energization. Further, since Zn and Si attract each other, it is difficult to form deep impurity levels in the active layer 104, so that a highly reliable semiconductor laser with a low threshold current can be realized.

Note that Si doped in the active layer 104 is preferably kept at a low concentration within a necessary limit so as not to form deep impurity levels at high density by itself, and is preferably 1 × 10 ¹⁶ cm ^{−3 to} 3 × 10 6. If it is in the range of ¹⁷ cm ⁻³ , the suppression of impurity diffusion and the suppression of deep impurity level formation can both be achieved.

  Further, in the present embodiment, the case where Si is used as the impurity doped in the p-type cladding layer and the impurity doped in the active layer is shown, but S, Te, or the like may be used.

  In this embodiment, an example of suppressing impurity diffusion from the p-type cladding layer is shown. However, a small amount of p-type impurity is doped in the n-type cladding layer, and further, p-type impurities are doped in the active layer. Alternatively, they may be combined, that is, a small amount of n-type impurity is doped in the p-type cladding layer, a small amount of p-type impurity is doped in the n-type cladding layer, and a small amount of n-type impurity is doped in the active layer. A configuration in which a p-type impurity and a p-type impurity are doped may be employed. In these cases, the position where the active layer is doped with impurities can be appropriately determined according to the state of impurity diffusion from each cladding layer.

  In the first to fourth embodiments, the AlGaInP red laser has been described. However, for example, the effects of the present invention can be obtained even if the present invention is applied to an AlGaAs infrared laser, a GaN semiconductor laser, or the like. In particular, in a monolithic two-wavelength laser, the same effect as that of the present embodiment can be realized when the cladding layer is made of an AlGaInP-based material even with an infrared laser.

  The present invention is not limited to the structure disclosed in the first to fourth embodiments, and can be arbitrarily set such as the composition of each layer, the film thickness, the electrode structure, and the structure of the resonator end face. The active layer may not have a quantum well structure, and the light guide layer may not be provided. For example, instead of the quantum well structure, a single thick light emitting layer is disposed.

(Embodiment 5)
Next, a fifth embodiment of the present invention will be described. The laminated structure is the same as that of the first embodiment, and the main difference is that Zn is present at the interface between the n-type cladding layer and the active layer and the active layer and the p-type cladding layer are Since the interface is Si-delta-doped, the structure will be briefly described with reference to FIGS.

An n-GaAs buffer layer 102 (Si-doped, 1.2 × 10 ¹⁸ cm ⁻³ ), 0.5 μm is formed on the n-GaAs substrate 101 (Si-doped, 1.0 × 10 ¹⁸ cm ⁻³ ). . The buffer layer 102 is necessary for improving the crystallinity of the cladding layers 103, 105, 107, the active layer 104, and the like described below.

On the n-GaAs buffer layer 102, an n- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer 103 (Si-doped, 1.2 × 10 ¹⁸ cm ⁻³ ) 2.0 μm, an active layer 104 (Si-doped) 92 nm, first p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer 105 (Zn doped, 5 × 10 ¹⁷ cm ⁻³ ) 175 nm, p-Ga _0.5 In _0.5 P etching stop layer 106 (Zn doped, 1 × 10 ¹⁸ cm ⁻³ ) 10 nm, second p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P clad layer 107 (Zn-doped, 1.1 × 10 ¹⁸ cm ⁻³ ) 1.0 μm, p-Ga _0.5 In _A double heterojunction structure having a _0.5 P contact layer 108 (Zn-doped, 1 × 10 ¹⁸ cm ⁻³ ) 50 nm is formed.

Here, after the active layer 104 is formed, Si delta doping (1.0 × 10 ¹⁷ cm ⁻³ ) is performed before the first p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer 105 is formed. After the delta doping, a first p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer 105 is formed.

  The composition of each of the above layers is an example, and the lattice constants of the double heterojunction layers 103 to 107 and the cap layer 108 are substantially equal to those of the n-GaAs substrate 101, and the cladding layers 103, 105, and 107, and the etching stop layer 106 are included. The composition of In, Ga, and Al is determined so that the band gap energy of the contact layer 108 is larger than the band gap energy of the active layer 104.

On the side of the second p- (Al _0.7 Ga _0.3 ) _0.5 In _0.5 P cladding layer 107 is an n-Al _0.5 In _0.5 P current blocking layer 109 (Si-doped, 5.0 × 10 ¹⁷ cm ⁻³ ) 300 nm. 2. A p-GaAs cap layer 110 (Zn-doped, 5 × 18 ¹⁸ cm ⁻³ ) is formed on the p-Ga _0.5 In _0.5 P cap layer 108 and the n-Al _0.5 In _0.5 P current blocking layer 109. 0 μm is formed. A p-side electrode 112 is formed on the upper surface of the p-GaAs cap layer 110, and an n-side electrode 111 is formed on the lower surface of the n-GaAs substrate 101. All layers except the p-side electrode 112 and the n-side electrode 111 are formed by crystal growth by the metal organic chemical vapor deposition layer method (MOCVD method).

Here, the manufacturing method of the window regions 113 and 114 is the same as that of the first embodiment.
The active layer 104 is a strained quantum well active layer, and four Ga _0.5 In _0.5 P well layers 202 (Si-doped, 1.0 × 10 ¹⁷ cm ⁻³ ) have a thickness of 5 nm and three layers between these layers. (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P barrier layer 203 (Si-doped, 1.0 × 10 ¹⁷ cm ⁻³ ) thickness of 5 nm and (Al _0.5 Ga _0.5 ) _0.5 In _0.5 P light guide layer 201 sandwiching them 204 (Si-doped, 1.0 × 10 ¹⁷ cm ⁻³ ) with a thickness of 28 nm.

Here, the operation of the semiconductor laser in the fifth embodiment will be specifically described.
The p-type cladding layer 105 is doped with Zn as a p-type impurity. Si that is an n-type impurity is relatively difficult to diffuse in an AlGaInP-based material, whereas Zn that is a p-type impurity is easily diffused.

  Therefore, Zn diffuses into the active layer 104 by heat treatment processes such as crystal growth and window structure formation processes and energization, and there is a possibility that the reliability of the laser is impaired by inducing defects due to impurity diffusion. Therefore, the active layer 104 is doped with Si in advance so that the movement of Zn can be suppressed even if Zn diffuses into the active layer 104, and further Si is delta-doped at the interface between the active layer 104 and the p-type cladding layer 105.

  FIG. 8 is a schematic diagram showing the state of impurity diffusion from the p-type cladding layer 105 to the active layer 104 in the present embodiment.

  As shown in FIG. 8, Zn, which is an impurity in the p-type cladding layer 105, and Si, which is an impurity of the opposite conductivity type, are present in advance at the interface between the active layer 104 and the active layer 104 and the p-type cladding layer 105. For example, Zn diffused in the active layer 104 and Si doped in the active layer 104 are attracted to each other by ionic bonding or the like, so that movement of Zn in the active layer 104 can be suppressed even during a thermal process or during energization. . Furthermore, the diffusion of Zn into the active layer can be suppressed by delta doping Si at the interface between the active layer 104 and the p-type cladding layer 105. In addition, since a deep impurity level is hardly formed in the active layer 104 by attracting Si and Mg to each other, a highly reliable semiconductor laser with a low threshold current can be realized.

Note that Si doped in the active layer 104 is preferably kept at a low concentration within a necessary limit so as not to form deep impurity levels at high density by itself, and is preferably 1 × 10 ¹⁶ cm ^{−3 to} 3 × 10 6. If it is in the range of ¹⁷ cm ⁻³ , the suppression of impurity diffusion and the suppression of deep impurity level formation can both be achieved.

  Further, in the present embodiment, the case where the impurity of the p-type cladding layer is Zn is shown, but the same effect as described above can be obtained when C, Be, Cd, or the like is used instead of Zn. is there.

  Further, when Se is used as the impurity of the n-type cladding layer described in the second embodiment, the active layer is doped with Mg in order to suppress the diffusion of the impurity from the n-type cladding layer to the active layer, and Further, by performing delta doping of Mg at the interface between the n-type cladding layer 103 and the active layer 104, it is possible to suppress further diffusion of Se into the active layer.

  When Se is used as the n-type cladding layer impurity and Zn is used as the p-type cladding layer impurity described in the third embodiment, not only the active layer is doped with Si and Mg but also the n-type cladding layer 103. Further, diffusion of impurities into the active layer can be suppressed by delta-doping Mg at the interface between the active layer 104 and Si at the interface between the active layer 104 and the p-type cladding layer 105.

  In the present embodiment, the entire active layer 104, that is, the light guide layers 201 and 204, the well layers 202A to 202D, and the barrier layer 203 are doped with Si, but by adjusting the crystal growth process or the like, The amount of Zn-type impurities that diffuse into the active layer 104 varies. When this amount is small, it is possible to sufficiently suppress the diffusion of the p-type impurity in the active layer 104 by doping part of the active layer 104 with Si. For example, only the light guide layer 201 may be doped with Si, Si may be doped from the light guide layer 201 to the well layer 202B, or Si may be doped from the light guide layer 201 to the well layer 202D.

  The semiconductor laser according to the present invention can realize a semiconductor laser having high output and high reliability, and is particularly useful when applied to a red semiconductor laser used for a DVD or the like.

Sectional view of the semiconductor laser in each embodiment of the present invention viewed from the cavity end face direction Sectional view of the semiconductor laser in each embodiment of the present invention viewed from the cavity length direction Laminated structure diagram of active layer of semiconductor laser in each embodiment of the present invention The schematic diagram which showed the mode of the impurity diffusion from the clad layer to an active layer in Embodiment 1 of this invention The schematic diagram which showed the mode of the impurity diffusion from the clad layer to the active layer in Embodiment 2 of this invention The schematic diagram which showed the mode of the impurity diffusion from the clad layer to the active layer in Embodiment 3 of this invention The schematic diagram which showed the mode of the impurity diffusion from the clad layer to the active layer in Embodiment 4 of this invention The schematic diagram which showed the mode of the impurity diffusion from the clad layer to an active layer in Embodiment 5 of this invention

Explanation of symbols

101 n-GaAs substrate 102 n-GaAs buffer layer 103 n-AlGaInP cladding layer 104 strained quantum well active layer (active layer)
105 first p-AlGaInP cladding layer 106 p-GaInP etching stop layer 107 second p-AlGaInP cladding layer 108 p-GaInP cap layer 109 n-AlInP current blocking layer 110 p-GaAs cap layer 111 n-electrode 112 p -Electrodes 201, 204 Light guide layers 202A-202D Well layers 203A-203C Barrier layers

Claims (21)

A semiconductor laser comprising: a first conductive clad layer and a second conductive clad layer; and an active layer positioned between the first conductive clad layer and the second conductive clad layer on a semiconductor substrate. There,
A semiconductor laser, wherein the active layer contains impurities. The semiconductor laser according to claim 1, wherein the active layer includes a quantum well or a single light emitting layer, a barrier layer, and a light guide region. The impurity in the active layer is an impurity having a conductivity type opposite to the impurity in the first conductivity type cladding layer,
The impurity in the first conductivity type cladding layer is a substance having a diffusion coefficient larger than that of the impurity in the active layer in the first conductivity type cladding layer or in the active layer. Or the semiconductor laser of 2. The impurity in the active layer is an impurity having a conductivity type opposite to the impurity in the second conductivity type cladding layer,
The impurity in the second conductivity type cladding layer is a substance having a larger diffusion coefficient than the impurity in the active layer in the second conductivity type cladding layer or in the active layer. Or the semiconductor laser of 2. The active layer contains an impurity having a conductivity type opposite to the impurity in the first conductivity type cladding layer, and an impurity having a conductivity type opposite to the impurity in the second conductivity type cladding layer,
The impurity in the first conductivity type cladding layer is a substance having a larger diffusion coefficient than the second conductivity type impurity in the active layer in the first conductivity type cladding layer or in the active layer,
The impurity in the second conductivity type cladding layer is a substance having a larger diffusion coefficient than the first conductivity type impurity in the active layer in the second conductivity type cladding layer or in the active layer. The semiconductor laser according to claim 1 or 2. 6. The semiconductor laser according to claim 1, wherein the concentration of impurities in the active layer is in a range of 1 × 10 ¹⁶ cm ^{−3 to} 3 × 10 ¹⁷ cm ⁻³ in total. The one or both of said 1st conductivity type clad layer and said 2nd conductivity type clad layer are co-doped with impurities of the conductivity type opposite to the impurities in each clad layer. A semiconductor laser according to claim 1. 8. The semiconductor laser according to claim 1, wherein among the impurities in the active layer, the impurity having the first conductivity type is any one of Si, S, and Te. 9. The semiconductor laser according to claim 1, wherein the impurity having the second conductivity type among the impurities in the active layer is any one of Mg, C, Be, and Cd. . The semiconductor laser according to claim 1, wherein the active layer is made of at least an AlGaInP-based material. The semiconductor laser according to claim 1, wherein the first conductivity type cladding layer and the second conductivity type cladding layer are made of at least an AlGaInP-based material. Forming a first conductivity type cladding layer on a semiconductor substrate while adding a first conductivity type impurity;
A second step of forming an active layer on the first conductivity type cladding layer;
A third step of forming a second conductivity type cladding layer while adding a second conductivity type impurity on the active layer, and a method of manufacturing a semiconductor laser,
In the second step, the active layer is formed while an impurity is added. A method for manufacturing a semiconductor laser. The semiconductor laser manufacturing method according to claim 12, wherein in the second step, the active layer having a multilayer structure is formed. In the second step, the active layer is formed while adding an impurity having a conductivity type opposite to the impurity in the first conductivity type cladding layer,
The impurity in the first conductivity type cladding layer is a substance having a larger diffusion coefficient than the impurity in the active layer in the first conductivity type cladding layer or in the active layer. Or a method for producing a semiconductor laser according to 13; In the second step, the active layer is formed while adding an impurity having a conductivity type opposite to the impurity in the second conductivity type cladding layer,
The impurity in the second conductivity type cladding layer is a substance having a larger diffusion coefficient than the impurity in the active layer in the second conductivity type cladding layer or in the active layer. Or a method for producing a semiconductor laser according to 13; In the second step, the active layer is formed while adding an impurity having a conductivity type opposite to the impurity in the first conductivity type cladding layer and an impurity having a conductivity type opposite to the impurity in the second conductivity type cladding layer. And
The impurity in the first conductivity type cladding layer is a substance having a larger diffusion coefficient than the second conductivity type impurity in the active layer in the first conductivity type cladding layer or in the active layer,
The impurity in the second conductivity type cladding layer is a substance having a larger diffusion coefficient than the first conductivity type impurity in the active layer in the second conductivity type cladding layer or in the active layer. A method of manufacturing a semiconductor laser according to claim 12 or 13. In the second step, the active layer is formed so that the total concentration of impurities in the active layer is in the range of 1 × 10 ¹⁶ cm ^{−3 to} 3 × 10 ¹⁷ cm ^−3. The method for manufacturing a semiconductor laser according to claim 12. In one or both of the first step and the third step, one or both of the first conductivity type cladding layer and the second conductivity type cladding layer are obtained by co-doping an impurity having a conductivity type opposite to the impurity in each cladding layer. The method of manufacturing a semiconductor laser according to claim 12, wherein the semiconductor laser is formed.   19. The method of manufacturing a semiconductor laser according to claim 12, further comprising a step of forming a window structure by diffusing impurities in the vicinity of a cavity end face of the semiconductor laser. At one or both of the interface between the active layer and the first conductivity type cladding layer and / or the interface between the active layer and the second conductivity type cladding layer, an impurity having a conductivity type opposite to the impurity in each cladding layer is delta-doped. The semiconductor laser according to any one of claims 1 to 6, wherein: The interface between the first conductivity type cladding layer formed in the first step and the active layer formed in the second step, and the interface between the active layer formed in the second step and the second step formed in the third step 18. The method of manufacturing a semiconductor laser according to claim 12, wherein an impurity in each clad layer and an anti-conductivity type impurity are delta-doped at the interface of the conductive clad layer.

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