JP2014011348A - Method of manufacturing semiconductor laser and method of manufacturing semiconductor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a semiconductor laser capable of increasing the p-dopant concentration of a cladding layer and preventing degradation of an active layer, and to provide a method of manufacturing a semiconductor element.SOLUTION: A method of manufacturing a semiconductor laser includes the steps of: providing a ground layer 10a on a substrate 10 composed of n-InP; providing an active layer 12 in contact with the ground layer 10a; providing a cladding layer 14 composed of p-InP on the active layer 12; providing an InGaAs layer 11 on the cladding layer 14; and diffusing Zn into the cladding layer 14 after the step of providing the InGaAs layer 11.

Description

  The present invention relates to a semiconductor laser manufacturing method and a semiconductor device manufacturing method, and more particularly to a semiconductor laser manufacturing method and a semiconductor device manufacturing method used for optical communication.

  In an optical semiconductor device using a compound semiconductor, an active layer responsible for carrier recombination and stimulated emission of light, and a cladding layer for confining carriers and light in the active layer are stacked in an axial direction, thereby improving efficiency. Carrier injection and increase in laser oscillation output are realized. For example, Patent Document 1 describes a technique using a clad layer formed of p-type indium phosphide (p-InP). In recent years, there has been a demand for semiconductor lasers that have high luminous efficiency and high light output at high temperatures in order to further reduce power consumption and use at high ambient temperatures. In order to increase luminous efficiency and light output, it is important to improve the crystal quality of the active layer and reduce the series resistance of the semiconductor element. In order to improve the crystal quality of the active layer, the diffusion of the p-type dopant from the p-type cladding layer to the active layer is required to be small. On the other hand, a reduction in the resistance of the p-type cladding layer is required to reduce the series resistance of the semiconductor element. This is because the series resistance of the p-type cladding layer accounts for about 90% of the total series resistance.

JP 2002-174746 A

  In order to reduce the resistance of the p-type cladding layer, it is important to increase the concentration of the p-type dopant added to the cladding layer. However, it is known that when the dopant concentration is increased, the p-type dopant diffuses into the active layer and the crystal quality of the active layer deteriorates. For this reason, as the p-type dopant, zinc (Zn), which has a relatively short diffusion distance and is difficult to deteriorate the active layer, is generally used. In view of the above problems, an object of the present invention is to provide a semiconductor laser manufacturing method and a semiconductor device manufacturing method capable of increasing the dopant concentration of the cladding layer and suppressing the deterioration of the active layer.

  The present invention includes a step of providing an underlayer on a substrate made of InP, a step of providing an active layer in contact with the underlayer, a step of providing a cladding layer made of InP on the active layer, And a step of diffusing Zn into the cladding layer after the step of providing a semiconductor layer made of InGaAs or InGaAsP and the step of providing the semiconductor layer.

  In the above structure, the base layer may include a region in contact with the active layer and be an n-type conductive semiconductor layer.

  The said structure WHEREIN: The area | region of 1/5 density | concentration of the peak of the p-type density | concentration in the said cladding layer can be set as the structure formed in the said cladding layer.

In the above configuration, the step of diffusing Zn includes a step of annealing in a gas atmosphere containing DMZ and AsH ₃ , and the temperature of the annealing treatment in the step of diffusing Zn is 470 ° C. or more and 560 ° C. or less. There can be a certain configuration.

  In the above structure, an electrode may be provided over the semiconductor layer.

  In the above configuration, the step of removing the semiconductor layer before the step of diffusing Zn, and the step of providing a contact layer made of InGaAs or InGaAsP on the cladding layer after the step of removing the semiconductor layer, And a step of providing an electrode on the contact layer.

  In the above configuration, the thickness of the contact layer may be larger than the thickness of the semiconductor layer.

The said structure WHEREIN: The peak value of Zn density | concentration of the said clad layer after the process of diffusing said Zn can be set as the structure which is 5 * 10 < ¹⁸ > cm < ^-3 > or more.

In the above configuration, when the thickness of the cladding layer is T and the diffusion coefficient of Zn in the cladding layer is D, the annealing time in the step of diffusing Zn is (T / D) ^0.5 or less. It can be configured.

  The present invention provides a step of providing an InP semiconductor layer, a step of providing a semiconductor layer made of InGaAs or InGaAsP on the InP semiconductor layer, and a step of diffusing Zn into the InP semiconductor layer after the step of providing the semiconductor layer. And a method for manufacturing a semiconductor device.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the manufacturing method of the semiconductor laser which can raise the dopant density | concentration of a clad layer, and can suppress degradation of an active layer, and the manufacturing method of a semiconductor element.

FIG. 1 is a cross-sectional view illustrating a semiconductor element having an SI-BH structure. 2A to 2C are cross-sectional views illustrating a method for manufacturing a semiconductor element according to the first embodiment. FIG. 3A and FIG. 3B are cross-sectional views illustrating a method for manufacturing a semiconductor element according to the first embodiment. FIG. 4A is a graph illustrating the relationship between the cladding layer depth and the dopant concentration. FIG. 4B is a graph illustrating the relationship between current and light output. FIG. 5A is a graph illustrating the relationship between the DMZ concentration and the dopant concentration in the source gas. FIG. 5B is a graph illustrating the relationship between the diffusion temperature and the dopant concentration. FIG. 6A is a graph illustrating the relationship between the diffusion time and the dopant concentration. FIG. 6B is a graph illustrating the relationship between the diffusion time and the resistance reduction rate. FIG. 7 is a cross-sectional view illustrating a semiconductor element having a pn-BH structure. FIG. 8A to FIG. 8C are cross-sectional views illustrating a method for manufacturing a semiconductor element according to the second embodiment. FIG. 9A and FIG. 9B are cross-sectional views illustrating a method for manufacturing a semiconductor element according to the second embodiment.

  First, the configuration of the semiconductor element will be described. FIG. 1 is a cross-sectional view illustrating a semiconductor laser 100 having an SI-BH (Semi-Insulating Buried-hetero) structure.

  As shown in FIG. 1, the semiconductor laser 100 includes a substrate 10, an active layer 12, a cladding layer 14, a contact layer 16, a buried layer 18, an n-type electrode 20 and a p-type electrode 22. The substrate 10 is formed of n-type indium phosphide (n-InP), and also functions as an n-type cladding layer. In FIG. 1, a base layer (not shown) is provided on the substrate 10. The active layer 12 is in contact with the underlying layer and is, for example, an InGaAsP / InGaAsP multiple quantum well layer formed of indium gallium arsenide phosphorus. The cladding layer 14 is in contact with the upper surface of the active layer 12 and is formed of p-InP. The clad layer 14 contains zinc (Zn) as a p-type dopant. A region 14a in the cladding layer 14 indicated by diagonal lines in the drawing is a region where the Zn concentration is increased by the diffusion process. For example, cadmium (Cd) can be used as the diffusing dopant. However, Zn has better controllability of concentration than Cd, and can easily suppress diffusion into the active layer 12. Zn is mainly diffused in the region 14a in the clad layer 14 indicated by diagonal lines in the drawing. In order to suppress the diffusion of Zn into the active layer 12, the region 14 a preferably does not reach the interface between the active layer 12 and the cladding layer 14.

  The contact layer 16 is made of, for example, p-type indium gallium arsenide (p-InGaAs) and is in contact with the upper surface of the cladding layer 14. The buried layer 18 is formed of, for example, iron-doped indium phosphide (Fe—InP), is in contact with the upper surface of the substrate 10, and sandwiches the active layer 12, the cladding layer 14, and the contact layer 16. The n-type electrode 20 is in contact with the lower surface of the substrate 10. The p-type electrode 22 is in contact with the upper surface of the contact layer 16 and the upper surface of the buried layer 18. The n-type electrode 20 and the p-type electrode 22 are made of a metal such as a mixed crystal of gold (Au) and germanium (Ge) or a mixed crystal of titanium (Ti) and platinum (Pt). The semiconductor laser 100 is used as a light emitting element.

As described above, in order to increase the luminous efficiency, it is important to reduce the resistance of the cladding layer 14. By increasing the Zn concentration (dopant concentration) in the cladding layer 14, the resistance of the cladding layer 14 can be reduced. The diffusion of Zn into the cladding layer 14 may be performed by vapor phase diffusion. In metal organic chemical vapor deposition (MOCVD), which is mainly used as a method for manufacturing the cladding layer 14, the dopant concentration is saturated at about 2 × 10 ¹⁸ cm ⁻³ . Therefore, even if the Zn concentration in the source gas is increased, it is difficult to increase the dopant concentration to a saturation value or higher. So far, Zn diffusion has sometimes been performed by vapor phase diffusion in order to increase the dopant concentration to 2 × 10 ¹⁸ cm ⁻³ or more. In vapor phase diffusion, for example, a gas containing dimethylzinc (DMZ) and phosphine (PH ₃ ) is used as a source gas for diffusion. In the source gas atmosphere, Zn is diffused by performing an annealing process for heating the clad layer 14. A problem that occurs in an example of performing vapor phase diffusion will be described.

In order to diffuse Zn into p-InP, vapor phase diffusion has been performed in an atmospheric gas containing DMZ and PH ₃ . This is because it was thought that Zn as a p-type dopant contained in p-InP and P as a group V element would not impair the crystal quality of p-InP by being contained in the atmospheric gas. Here, the annealing temperature (diffusion temperature) for vapor phase diffusion is determined by the ease of desorption of DMZ from the semiconductor surface and the difficulty of PH ₃ decomposition. That is, DMZ has a small desorption energy from the surface of a solid and is easily evaporated. For this reason, the efficiency of Zn incorporation into the cladding layer 14 increases as the annealing temperature (diffusion temperature) is lower. For example, the dopant concentration can be set to a high concentration of 2 × 10 ¹⁸ cm ⁻³ or more at a diffusion temperature of 560 ° C. or less. On the other hand, in order to decompose PH ₃ and generate P molecules, it is required to increase the diffusion temperature to 560 ° C. or higher. Therefore, when an atmospheric gas containing DMZ and PH ₃ is used, it has been difficult to set a diffusion temperature that can achieve both Zn uptake and PH ₃ decomposition. For example, when the diffusion temperature is 560 ° C. or lower, PH ₃ is taken into the cladding layer 14 together with hydrogen without being decomposed. As a result, in the clad layer 14, P, hydrogen, and Zn are combined, and so-called hydrogen passivation occurs. That is, Zn is deactivated and does not function as a p-type dopant. In order to use the deactivated Zn as a p-type dopant, it is necessary to perform a second annealing process at a diffusion temperature of 560 ° C. or higher, for example, in a hydrogen (H ₂ ) atmosphere. However, when annealing is performed twice in total at a temperature of 560 ° C. or more, the diffusion distance of Zn increases and diffuses into the active layer 12. As a result, the crystal quality of the active layer 12 deteriorates, and as a result, the light emission efficiency decreases. Next, Example 1 will be described.

Example 1 is an example in which Zn is diffused using DMZ and arsine (AsH ₃ ). FIG. 2A to FIG. 3B are cross-sectional views illustrating a method for manufacturing the semiconductor laser 100 according to the first embodiment.

As shown in FIG. 2A, the base layer 10 a is formed on the substrate 10. The underlayer 10a is formed of n-InP and includes a diffraction grating (grating, not shown) formed of InGaAsP. In FIG. 2B and subsequent figures, the base layer 10a is omitted. For example, the active layer 12 and the cladding layer 14 are grown on the underlayer 10a by using MOCVD (Metal Organic Chemical Vapor Deposition). The active layer 12 is in contact with the base layer 10a. The thickness of the substrate 10 is, for example, 350 μm, the thickness of the active layer 12 is, for example, 0.3 μm, and the thickness of the cladding layer 14 is, for example, 2 μm. The source gas of the active layer 12 includes, for example, trimethyl indium (TMIn), triethyl gallium (TEGa), PH ₃ and AsH ₃ . The source gas for the cladding layer 14 includes TMIn, DMZ, PH ₃ , AsH _3, and H ₂ . The concentration of DMZ in the raw material gas is, for example, a volume concentration of 0.0008%. The temperature (growth temperature) in the MOCVD apparatus is, for example, 630 ° C., and the pressure (growth pressure) is, for example, 0.1 atm (98067 Pa). In the growth of the contact layer 16 and the buried layer 18 described later, for example, the same growth temperature and growth pressure are used.

As shown in FIG. 2B, an indium gallium arsenide (InGaAs) layer 11 that contacts the upper surface of the cladding layer 14 is grown by using, for example, the MOCVD method. The source gas includes, for example, TMIn, TEGa, and AsH ₃ . The thickness of the InGaAs layer 11 is 0.1 μm, for example. After forming the InGaAs layer 11, annealing is performed to diffuse Zn into the cladding layer 14. That is, the step of diffusing Zn includes a step of performing an annealing process. The temperature (diffusion temperature) in the furnace used for the annealing treatment is, for example, 520 ° C., and the pressure is, for example, 80 torr (10664 Pa). The source gas contains DMZ, AsH ₃ and H ₂ . The concentration of DMZ in the raw material gas is, for example, 0.09%, and the concentration of AsH ₃ is, for example, 0.09%. The annealing time (diffusion time) is, for example, 3 minutes. A region 14a in which Zn diffuses is formed by the annealing process.

As shown in FIG. 2C, for example, a liquid mixture of hydrofluoric acid and nitric acid is used as an etchant to remove the InGaAs layer 11. For example, the contact layer 16 having a thickness of 0.5 μm, for example, is grown on the upper surface of the cladding layer 14 by using MOCVD. The source gas includes, for example, TMIn, TEGa, DMZ, and AsH ₃ . By subjecting the InGaAs layer 11 to the process of diffusing Zn, the crystallinity of the InGaAs layer 11 is lowered and the surface becomes rough. Thus, since the adhesion between the InGaAs layer 11 and the electrode after the step of diffusing Zn deteriorates, the InGaAs layer 11 is not suitable as a contact layer. Therefore, it is preferable to remove the InGaAs layer 11 after the step of diffusing Zn and form the contact layer 16 made of InGaAs on the cladding layer 14 again. The contact layer 16 is preferably thicker than the InGaAs layer 11. This is because if the thickness of the InGaAs layer 11 is large, the diffusion time becomes long and Zn is diffused into the active layer 12. On the other hand, in the process of alloying with the electrode, if the thickness of the contact layer 16 is small, the cladding layer 14 is alloyed. Therefore, by increasing the thickness of the contact layer 16, the cladding layer 14 is alloyed. It is because it suppresses.

As shown in FIG. 3A, a mask 13 made of silicon dioxide (SiO ₂ ) is formed on the upper surface of the contact layer 16. For example, the active layer mesa stripe 15 is formed by dry etching. As shown in FIG. 3B, a buried layer 18 having a thickness of, for example, 3 μm is grown on the active layer mesa stripe 15 by using, for example, the MOCVD method. The source gas includes, for example, TMIn, cyclopentanedienyl iron (Cp ₂ Fe), and H ₂ . For example, the mask 13 is immersed in hydrofluoric acid for 1 minute, and the mask 13 is removed. For example, the n-type electrode 20 and the p-type electrode 22 are formed by vapor deposition. Thereby, the semiconductor laser 100 is formed.

According to Example 1, since the InGaAs layer 11 whose solid solubility limit with respect to Zn is an order of magnitude higher than that of InP is used as the solid phase diffusion source, the dopant concentration of the cladding layer 14 can be increased. Further, the source gas in the annealing process includes DMZ and AsH ₃ . Since the decomposition energy of AsH ₃ is smaller than the decomposition energy of PH ₃ , a diffusion temperature range in which Zn uptake and AsH ₃ decomposition can be achieved can be determined as described later.

  The dopant concentration was measured in Example 1 and the comparative example. An example of growing p-InP while adding Zn before Zn diffusion by annealing will be described as a comparative example.

FIG. 4A is a graph illustrating the relationship between the depth of the cladding layer 14 and the dopant concentration. The horizontal axis represents the depth of the cladding layer 14 with respect to the upper surface of the cladding layer 14, and the vertical axis represents the dopant concentration. A broken line indicates a measurement result in the comparative example, and a solid line indicates a measurement result in Example 1. As shown in FIG. 4A, in the comparative example, the dopant concentration is about 2 × 10 ¹⁸ cm ⁻³ at the maximum. In Example 1, the dopant concentration is about 5 × 10 ¹⁸ cm ⁻³ at maximum. When the depth is 1 μm or more, the dopant concentration decreases. The dopant concentration is 1 × 10 ¹⁸ cm ⁻³ at a depth of about 2 μm, that is, in the vicinity of the lower surface of the cladding layer 14. The boundary between the region 14 a and the cladding layer 14 does not reach the active layer 12.

As described above, the solid solution limit of Zn to InGaAs is about 1 × 10 ¹⁹ to 2 × 10 ¹⁹ cm ^−3, which is one digit higher than the solid solution limit of Zn to InP. By using the InGaAs layer 11 as the solid phase diffusion source of Zn, the concentration of Zn in the cladding layer 14 can be increased as compared with the case where Zn is vapor-phase diffused as in the comparative example. Further, since the dopant concentration is low in the vicinity of the lower surface of the cladding layer 14, the diffusion of Zn into the active layer 12 can be suppressed. As described above, according to the first embodiment, the dopant concentration of the cladding layer 14 can be increased and the deterioration of the active layer 12 can be suppressed. In the experiment described in FIG. 4A, a region having a concentration (1 × 10 ¹⁸ cm ⁻³ ) that is 1/5 of the peak of the dopant concentration (about 5 × 10 ¹⁸ cm ⁻³ ) is formed in the cladding layer 14. Is done. For example, it is more preferable that a region having a concentration of 1/10 or less of the peak of the dopant concentration is formed in the cladding layer 14. In order to reduce the resistance of the cladding layer 14, the peak value of the dopant concentration is preferably 5 × 10 ¹⁸ cm ⁻³ or more.

  FIG. 4B is a graph illustrating the relationship between current and light output. The horizontal axis represents the current injected into the semiconductor laser 100, and the vertical axis represents the optical output of the semiconductor laser 100. As shown in FIG. 4B, in the comparative example, the current is 200 mA, the light output is about 40 mW, and is almost saturated. The light output of Example 1 does not saturate even at 200 mA or more, and rises as the current increases. In Example 1, the relationship between current and light output shows better linearity than the comparative example. Therefore, a high light output can be obtained by injecting a high current.

  In Example 1, the change in the dopant concentration of the cladding layer 14 was measured by changing the DMZ concentration, the diffusion temperature of the annealing treatment, and the diffusion time. First, an example in which the DMZ concentration is changed will be described.

FIG. 5A is a graph illustrating the relationship between the DMZ concentration and the dopant concentration in the source gas. The horizontal axis represents the DMZ concentration in the source gas used for diffusion, and the vertical axis represents the dopant concentration. A black dot is a measurement result, and a solid line is a calculation result of a dopant concentration based on the measurement result. As shown in FIG. 5A, the dopant concentration increases as the DMZ concentration increases. When the DMZ concentration is about 0.02%, the dopant concentration is about 2 × 10 ¹⁸ cm ⁻³ which is the saturation value of the comparative example shown in FIG. In order to obtain a high dopant concentration, the DMZ concentration is preferably 0.02% or more, and may be 0.025% or more, 0.03% or more, 0.05% or more, for example.

Next, the optimum range of the diffusion temperature will be described. As described above, since DMZ easily evaporates, the higher the diffusion temperature, the lower the efficiency of Zn incorporation into the cladding layer 14. On the other hand, AsH ₃ is more easily decomposed than PH ₃ and hardly decomposes at 470 ° C. or lower. In order to achieve both Zn uptake and AsH ₃ decomposition, the diffusion temperature is preferably 470 ° C. or higher and 560 ° C. or lower, for example.

FIG. 5B is a graph illustrating the relationship between the diffusion temperature and the dopant concentration. The horizontal axis represents the diffusion temperature, and the vertical axis represents the dopant concentration. As shown in FIG. 5B, the dopant concentration is about 5 × 10 ¹⁸ cm ⁻³ at about 520 ° C., which is the maximum. At 470 ° C. and 560 ° C., the dopant concentration is about 2 × 10 ¹⁸ cm ⁻³ . In the range of 470 ° C. or higher and 560 ° C. or lower, Zn uptake and AsH ₃ decomposition can both be achieved, and a higher dopant concentration than in the comparative example can be obtained. The diffusion temperature may be, for example, 480 ° C. or higher, 490 ° C. or higher, 550 ° C. or lower, and 540 ° C. or lower.

An example in which the diffusion time is changed will be described. FIG. 6A is a graph illustrating the relationship between the diffusion time and the dopant concentration. The horizontal axis represents the diffusion time, and the vertical axis represents the dopant concentration. The solid line is the calculation result of the dopant concentration obtained by logarithmically approximating the measurement result. The longer the diffusion time, the higher the dopant concentration. As indicated by the dotted line, the dopant concentration is about 2 × 10 ¹⁸ cm ⁻³ at a diffusion time of about 20 seconds. Therefore, a high dopant concentration can be obtained by setting the diffusion time to 20 seconds or longer.

  The resistance reduction rate (resistance reduction rate) of the cladding layer 14 was simulated. In the semiconductor laser 100, the resonator length is 300 μm, and the width of the active layer 12 is 1.2 μm. FIG. 6B is a graph illustrating the relationship between the diffusion time and the resistance reduction rate. The horizontal axis is the diffusion time, and the vertical axis is the resistance reduction rate. The longer the diffusion time, the higher the resistance reduction rate. When the diffusion time is about 0.5 minutes, the resistance reduction rate exceeds 10%. By setting the diffusion time to 3 minutes, the resistance is halved.

拡散距離Ｘがクラッド層１４の厚さＴを超えると、Ｚｎが活性層１２に拡散する。従って、拡散距離Ｘが厚さＴとなる拡散時間を拡散時間の上限ｔ_ｍａｘと定めることが好ましい。拡散方程式に基づき、拡散時間の上限ｔ_ｍａｘは次式で与えられる。

活性層１２へのＺｎの拡散を抑制するため、拡散時間ｔはｔ_ｍａｘ以下、又は未満であることが好ましい。 In order to suppress the diffusion of Zn into the active layer 12, it is preferable to adjust the diffusion time according to the thickness of the cladding layer 14. The diffusion distance X of Zn into the cladding layer 14 is given by the following diffusion equation. t is the diffusion time, D is the diffusion coefficient

When the diffusion distance X exceeds the thickness T of the cladding layer 14, Zn diffuses into the active layer 12. Therefore, it is preferable to set the diffusion time at which the diffusion distance X is the thickness T as the upper limit t _{max of the} diffusion time. Based on the diffusion equation, the upper limit t _{max of the} diffusion time is given by:

In order to suppress the diffusion of Zn into the active layer 12, the diffusion time t is preferably t _max or less or less.

  Example 2 is an example of a pn-BH (pn-Buried hetero: pn buried) structure. FIG. 7 is a cross-sectional view illustrating a semiconductor laser 200 having a pn-BH structure.

  As shown in FIG. 7, the semiconductor laser 200 includes a substrate 10, an active layer 12, a cladding layer 14, buried layers 24 and 26, an n-type electrode 20, and a p-type electrode 22. The buried layer 24 is made of, for example, p-InP. The buried layer 26 is made of, for example, n-InP and is in contact with the upper surface of the buried layer 24. The clad layer 14 is in contact with the upper surface of the buried layer 26.

  FIG. 8A to FIG. 9B are cross-sectional views illustrating a method for manufacturing the semiconductor laser 200 according to the second embodiment. As shown in FIG. 8A, an active layer 12 is grown on the substrate 10 using MOCVD. Further, the first layer 14b of the cladding layer 14 is grown on the active layer 12 by using the MOCVD method. The thickness of the first layer 14b is, for example, 0.5 μm. The growth conditions (raw material gas, growth temperature, and growth pressure) are the same conditions as in Example 1, for example.

As shown in FIG. 8B, a mask 13 is provided on the first layer 14b. For example, the active layer mesa stripe 15 is formed by dry etching. As shown in FIG. 8C, the buried layer 24 is grown on the active layer mesa stripe 15 by using, for example, the MOCVD method. A buried layer 26 is grown on the buried layer 24 using MOCVD. The growth conditions of the buried layer 24 are the same as those of the cladding layer 14, for example. The source gas for the buried layer 26 includes, for example, TMIn, disilane (SiH ₆ ), and PH ₃ . The growth temperature and growth pressure of the buried layer 26 are the same as those of the buried layer 24, for example.

  As shown in FIG. 9A, after removing the mask 13, the second layer 14c is grown. The thickness of the second layer 14c is, for example, 1.5 μm. The first layer 14b and the second layer 14c form the cladding layer 14. As shown in FIG. 9B, the InGaAs layer 11 is grown on the cladding layer 14. Zn is diffused into the clad layer 14 by annealing. The diffusion temperature is 500 ° C., for example. The source gas, pressure, and diffusion time are the same as in Example 1. After the annealing process, the InGaAs layer 11 is removed, and the contact layer 16, the n-type electrode 20, and the p-type electrode 22 are formed. Thereby, the semiconductor laser 200 is formed.

  According to the second embodiment, as in the first embodiment, the dopant concentration can be increased and the deterioration of the active layer 12 can be suppressed. By forming the buried layer 24 of, for example, Fe—InP, the semiconductor laser 200 may have a SIPBH (Semi-Insulating Planar Buried hetero) structure. The growth conditions of the buried layer 24 formed of Fe—InP are the same as the growth conditions of the contact layer 16, for example.

  In the first and second embodiments, the InGaAs layer 11 is removed and the contact layer 16 is formed. However, the InGaAs layer 11 may be used as a contact layer. That is, the p-type electrode 22 may be provided on the InGaAs layer 11 without removing the InGaAs layer 11. The underlayer 10a may be an n-type conductive semiconductor layer other than the n-InP layer. In addition to the InGaAs layer 11, for example, a semiconductor layer containing indium gallium arsenide phosphorus (InGaAsP) may be provided on the cladding layer 14. The solid phase diffusion source may include InGaAs or InGaAsP. Moreover, although Example 1 and Example 2 explained in full detail about the semiconductor laser, it is effective in the process of using diffusion in order to increase the dopant concentration of the semiconductor layer, and may be applied to semiconductor elements other than the semiconductor laser.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to such specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

DESCRIPTION OF SYMBOLS 10 Substrate 10a Underlayer 12 Active layer 11 InGaAs layer 14 Clad layer 16 Contact layer 18, 24, 26 Buried layer 22 P-type electrode 100, 200 Semiconductor laser

Claims (10)

Providing an underlayer on a substrate made of InP;
Providing an active layer in contact with the underlayer;
Providing a cladding layer made of InP on the active layer;
Providing a semiconductor layer made of InGaAs or InGaAsP on the cladding layer;
And a step of diffusing Zn in the cladding layer after the step of providing the semiconductor layer.   2. The method of manufacturing a semiconductor laser according to claim 1, wherein the underlayer includes a region in contact with the active layer and is an n-type conductive semiconductor layer.   2. The method of manufacturing a semiconductor laser according to claim 1, wherein a region having a concentration of 1/5 of the peak of the p-type concentration in the cladding layer is located in the cladding layer. The step of diffusing Zn includes a step of performing an annealing process in a gas atmosphere containing DMZ and AsH ₃ .
2. The method of manufacturing a semiconductor laser according to claim 1, wherein the annealing temperature in the step of diffusing Zn is not less than 470.degree. C. and not more than 560.degree.   2. The method of manufacturing a semiconductor laser according to claim 1, further comprising a step of providing an electrode on the semiconductor layer. Removing the semiconductor layer before the step of diffusing Zn;
A step of providing a contact layer made of InGaAs or InGaAsP on the cladding layer after the step of removing the semiconductor layer;
The method of manufacturing a semiconductor laser according to claim 1, further comprising a step of providing an electrode on the contact layer.   7. The method of manufacturing a semiconductor laser according to claim 6, wherein a thickness of the contact layer is larger than a thickness of the semiconductor layer. 2. The method of manufacturing a semiconductor laser according to claim 1, wherein a peak value of Zn concentration of the cladding layer after the step of diffusing Zn is 5 × 10 ¹⁸ cm ⁻³ or more. When the thickness of the cladding layer is T and the diffusion coefficient of Zn in the cladding layer is D, the annealing treatment time in the step of diffusing Zn is (T / D) ^0.5 or less. A method of manufacturing a semiconductor laser according to claim 4. Providing an InP semiconductor layer;
Providing a semiconductor layer made of InGaAs or InGaAsP on the InP semiconductor layer;
And a step of diffusing Zn in the InP semiconductor layer after the step of providing the semiconductor layer.

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