JPH0888432A - Production of semiconductor laser - Google Patents

Abstract

PURPOSE: To easily control the current injection area even a in semiconductor laser using a gallium nitride-based compound semiconductor by providing an n-type layer, active layer and p-type layer on a substrate, activating a p-type layer in the current injection area of the piled-up semiconductor layers and keeping a p-type layer other than it in an in active state. CONSTITUTION: An n-type low-temperature buffer layer 2, n-type hightemperature buffer layer 3, n-type clad layer 4, active layer 5, and p-type clad layer 6 are formed in sequence on a substrate 1. Next, a p-type contact layer 7 is formed in order to reduce the contact resistance against a p-type electrode. Then, the joint of H with Mg or Zn as dopant for the p-type layer is released and activated to reduce the resistance. That is, the whole substrate in which the semiconductor layers are piled up is put into a furnace of nitrogen atmosphere so as to be heated at 400 to 800 deg.C. Further, an inactivating treatment is applied to the non-injection area of current. Namely, a protection layer 8 is provided on the surface of the semiconductor layer consisting of only current injection area, and it is heated at 400 to 800 deg.C in an atmosphere containing H.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor laser. More specifically, the present invention relates to a semiconductor laser suitable for a gain waveguide structure in which a current non-injection region is made to have high resistance and a current injection region is controlled by using a gallium nitride based compound semiconductor suitable for blue light emission.

Here, a gallium nitride compound semiconductor is a compound of a group III element Ga and a group V element N or
A semiconductor made of a compound in which a part of Ga of the group III element is replaced with another group III element such as Al and In and / or a part of N of the group V element is replaced with another group V element such as P and As. Say.

[0003]

2. Description of the Related Art As a waveguide structure of a semiconductor laser, a refractive index waveguide structure and a gain waveguide structure are generally known. The refractive index guiding structure has a refractive index difference in the direction parallel to the active layer to confine and guide light, and it is possible to obtain single transverse mode oscillation up to high output operation. High return light-induced noise is likely to occur. On the other hand, the gain waveguide structure is a structure having no refractive index difference in the lateral direction, and the transverse mode is unstable and a kink is likely to occur, but since the longitudinal multimode oscillation occurs, the return light noise is small.

The simplest structure for controlling the current injection region of this gain waveguide structure is to pattern the electrodes as shown in FIGS. A structure to be an implantation region (see FIG. 4A),
A structure in which protons are implanted into both sides of the current injection region to increase the resistance (see FIG. 4B), or a structure in which both sides of the current injection region are removed by etching to form a mesa shape (FIG. 4).
(See (c)) is used. In FIG. 4, reference numeral 21 denotes, for example, an n-type GaAs substrate, on which a n-type clad layer 22, an active layer 23, and a p-type clad layer 24 are sequentially laminated to constitute a semiconductor laser having a double heterojunction structure. Is a p-side electrode, 26 is an n-side electrode, and 27 is a proton implantation region.

On the other hand, a light emitting diode (hereinafter referred to as LED) using a gallium nitride based compound semiconductor was developed,
In addition to conventional red and green LEDs, LEDs with high brightness in blue can be obtained, and there is a demand for development of blue semiconductor lasers in semiconductor lasers. In the LED using the gallium nitride-based compound semiconductor, when the p-type layer is epitaxially grown, in addition to Ga and N, the p-type dopants Mg and Zn are H ₂ as a carrier gas and NH ₃ as a reaction gas.
Since it easily binds to H and does not sufficiently function as a dopant, an activation treatment by annealing after growth of the p-type layer is performed to separate the bond between Mg and Zn and H to reduce the resistance. There is.

[0006]

In the conventional semiconductor laser of the electrode stripe type structure, as the distance from the electrode increases, the current does not contribute to light emission due to the diffusion of the current from the width of the electrode stripe. Since the operating voltage of a gallium-based compound semiconductor is about 3 V, if there is a large amount of leakage current, the amount of electric power that does not contribute to light emission also increases and there is a problem in that the light emission efficiency decreases.

Further, in the method of implanting protons or the like into the current non-injection regions on both sides of the electrode stripe to increase the resistance, there is a problem in that a device for implanting protons becomes large in size and is not suitable for mass production at low cost.

In the method of further etching into a mesa shape, it takes a long time to perform the etching, and it is particularly difficult to etch the gallium nitride-based compound semiconductor layer. Whether the wet etching is performed at a high temperature of 250 ° C. or higher. Reactive ion etching has to be performed in a chlorine gas atmosphere, and there is a problem that the work is difficult.

The present invention solves such a problem, the reactive current is small, the current injection region can be controlled by a simple manufacturing method, and the current injection region is simple even in a semiconductor laser using a gallium nitride based compound semiconductor. It is to provide a method of manufacturing a semiconductor laser that can be controlled in a stable manner.

[0010]

According to the method of manufacturing a semiconductor laser of the present invention, (a) a gallium nitride based compound semiconductor which comprises at least an n-type layer, an active layer and a p-type layer on a substrate and constitutes a semiconductor laser is provided. And (b) activating the p-type layer in the current injection region of the laminated semiconductor layer, and (c) deactivating the p-type layer in the region other than the current injection region of the laminated semiconductor layer. It is characterized by maintaining.

The stacked semiconductor layers are an n-type buffer layer, an n-type clad layer, an active layer, a p-type clad layer and a p-type clad layer.
The type contact layer is preferable for producing a semiconductor laser made of a gallium nitride based compound semiconductor.

After the semiconductor layers are stacked, the entire substrate is heat-treated to activate the p-type layer, and then a protective film is provided on the surface of the current injection region and heat-treated in an atmosphere containing hydrogen. It is preferable to inactivate the region other than the current injection region because the resistance of the current non-injection region can be surely increased and the current injection region can be controlled.

The heat treatment for activating the p-type layer is performed at 400 to 800 ° C. in a nitrogen atmosphere, even if the heat treatment is performed without providing a protective film on the surface of the semiconductor layer. N in the semiconductor layer is less likely to evaporate and deterioration of the semiconductor layer does not occur in a simple process, which is preferable.

By irradiating only the current injection region with an electron beam after the semiconductor layers are stacked to activate only the current injection region of the p-type layer, the current injection region can be easily formed with the fewest number of steps. It is preferable because it can be controlled.

[0015]

According to the method of manufacturing a semiconductor laser of the present invention, in the p-type layer of the gallium nitride based compound semiconductor layer, Mg or Zn as the dopant is H in the carrier gas or the reaction gas in the film forming process.
By utilizing the property of being easily combined with and deactivating, the current injection region of the p-type layer is annealed by heat treatment or electron beam irradiation to separate and release H combined with Mg and Zn. The resistance becomes low, and the current non-injection region combines the dopants Mg and Zn with H, or vaporizes N in the gallium nitride-based compound semiconductor to make it n-type, which makes the dopant difficult to move and inactive. , P-type impurities are thinned, resulting in high resistance.

That is, after forming a p-type layer of a gallium nitride-based compound semiconductor, the whole is heat-treated to activate the p-type layer, and then a protective film is formed only on the surface of the current injection region to form H. _By performing heat treatment in an atmosphere of H such as ₂ gas or NH ₃ gas, invasion of H can be prevented in a portion where the protective film is present, and evaporation of N or the like from the semiconductor layer can be prevented. There is no H in the semiconductor layer
Penetrates, combines with the dopants Mg and Zn and becomes inactive, and N evaporates from the semiconductor layer to become n-type.
Therefore, by providing a protective film on the surface of the current injection region and performing sufficient heat treatment in an atmosphere containing H, it is possible to increase the resistance only in the current non-injection region.

Further, the passivation during the epitaxial growth of the p-type layer is utilized, or after the passivation of the p-type layer is further advanced in a hydrogen atmosphere, the electron beam is irradiated only to the current injection region. The electron beam irradiation can be controlled finely by
Since it is possible to reduce the resistance by annealing only the irradiated portion at a high temperature, it is possible to control the current injection region with high accuracy.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method of manufacturing a semiconductor laser according to the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a sectional view showing a process of one embodiment (embodiment 1) of the method for manufacturing a semiconductor laser according to the present invention, and FIG. 2 is a sectional view showing one process of another embodiment (embodiment 2).

According to the present invention, as described above, in the p-type layer of the gallium nitride based compound semiconductor, the dopants Mg and Zn combine with H in the epitaxial growth process to make it difficult to move. This is based on the finding that it does not function as a p-type layer of resistance. That is, in a semiconductor light emitting device using a gallium nitride-based compound semiconductor, the p-type dopant does not sufficiently function as a dopant only by epitaxially growing the p-type layer, and therefore, the dopant Mg or Zn is not exposed by heat treatment or electron beam irradiation. Although the bond between H and H is cut off for activation, in the present invention, the property that the dopant Mg or Zn and the bond between H and H tend to be inactivated.
By utilizing the property that N is easily evaporated from the gallium nitride based compound semiconductor by heat treatment and becomes n-type by heat treatment, the p-type layer only in the current injection region is activated, and the p-type layer in the current non-injection region is epitaxially grown. The current injection region is controlled by maintaining the inactivated state that sometimes occurs or by further inactivating it by combining with H.

As a method of activating the current injection region and deactivating the current non-injection region, the entire p-type layer is activated by heat treatment or electron beam irradiation, and then the p-type layer having only the current non-injection region is activated. Is combined with H to bring it into an inactivated state, and N of the gallium nitride-based compound semiconductor layer is combined.
Of the p-type layer by evaporating the n-type to make it have a high resistance, and the whole p-type layer is inactivated by heat treatment in a hydrogen atmosphere during or after the epitaxial growth of the p-type layer, and only the current injection region is p-typed. There is a method of activating the mold layer. Less than,
It will be described in more detail with reference to specific examples.

Example 1 In this example, after a semiconductor layer made of a gallium nitride-based compound semiconductor constituting a semiconductor laser was laminated on a substrate,
The whole is annealed and activated by heat treatment, and then a protective film is provided only on the surface of the current injection region to remove H ₂ gas and NH.
By heat treatment in an atmosphere containing H such as ₃ , H is caused to penetrate into the semiconductor layer without the protective film, and M
While combining with a p-type dopant such as g or Zn,
Controlling the current injection region by evaporating N in the gallium nitride-based compound semiconductor to increase its resistance and preventing the invasion of H by the protective film to maintain the activated state and lower the resistance. Is. The manufacturing method of the present invention will be described in detail with reference to FIG.

First, as shown in FIG. 1 (a), a substrate 1 made of sapphire (Al ₂ O ₃ single crystal) or the like is provided with 40
Trimethylgallium (hereinafter, referred to as TMG) which is an organic metal compound gas, NH ₃ and SiH ₄ as a dopant together with a carrier gas H ₂ by a metal organic compound vapor phase growth method (hereinafter, referred to as MOCVD method) at a low temperature of 0 to 700 ° C. Alternatively, GeH ₄ , SnH ₄ , TeH ₄ or the like is supplied to form the low temperature buffer layer 2 made of n-type GaN with 0.0
1 ~ 0.2μm, then 700 ~ 1200 ℃
The high temperature buffer layer 3 made of n-type GaN having the same composition is formed at a high temperature of about 2 to 5 μm.

Then, a source gas of trimethylaluminum (hereinafter referred to as TMA) is further added to the above gas,
n-type Al _x Ga containing n-type dopant such as Si
_{A 1-xN} (0 <x <1) layer is formed, and an n-type cladding layer 4 for forming a double heterojunction is formed to have a thickness of about 0.1 to 0.3 μm.

Next, a material whose band gap energy is smaller than that of the cladding layer, such as trimethylindium (hereinafter
Introducing TMI), Ga _y In _1-y N (0 <y ≦
The active layer 5 composed of 1) is formed to a thickness of about 0.05 to 0.1 μm.

Further, the same raw material gas as that used for forming the n-type cladding layer 4 is used, and the impurity raw material gas is replaced with SiH ₄ or the like, and Mg or Zn is replaced with biscyclopentadienyl magnesium (hereinafter referred to as Cp ₂ Mg) or dimethylzinc (hereinafter referred to as DMZn) and introduced into the reaction tube to form the p-type clad layer 6 of p-type Al _x.
The Ga _1-x N layer is vapor-grown. As a result, a double heterojunction is formed by the n-type clad layer 4, the active layer 5, and the p-type clad layer 6.

Next, in order to form the p-type contact layer 7 for reducing the contact resistance with the p-type electrode, the same gas as the buffer layer 3 is used as Cp ₂ Mg as an impurity gas.
Alternatively, DMZn may be supplied to form a p-type GaN layer of 0.3 to 2
The growth of about μm is completed, and the stacking of the semiconductor layers is completed.

Next, Mg or Z which is a dopant for the p-type layer
A process of reducing the resistance by separating and activating the bond between n and H is performed. That is, the whole substrate on which the semiconductor layers are stacked is put in a furnace in a nitrogen atmosphere and 400 to 800 ° C.
Heat treatment is performed for about 20 to 60 minutes under about 1 atmosphere.
In this case, N and Ga in the gallium nitride-based compound semiconductor, especially N are easily vaporized because the whole temperature becomes high during the heat treatment, but the atmosphere gas in the furnace is nitrogen. However, only H, which can prevent the evaporation and is easy to evaporate, has its bond with Mg or the like cut off and evaporates. In order to prevent the evaporation of N and Ga, it is not 1 atm but 2
Even if the pressure is about 100 atm, H easily evaporates.
A reliable activation process can also be performed. By carrying out in a nitrogen atmosphere as described above, it is possible to prevent evaporation of N and Ga without providing a protective film on the surface, which is preferable.

Next, the non-injection region of the current is inactivated (see FIG. 1B). Specifically, SiO ₂ , Si ₃ N ₄ , Al ₂ O ₃ is formed on the surface of the semiconductor layer only in the current injection region.
A protective film 8 such as 0.05 to 0.3 μm is provided, and H ₂
Heat treatment is performed at 400 to 800 ° C. for 20 to 60 minutes in a gas atmosphere (for example, 1 atm) in which gas or H such as NH ₃ exists. By the heat treatment, H in the atmosphere penetrates into the semiconductor layer of the p-type layer and is combined with the dopants Mg, Zn and the like to be inactivated, resulting in high resistance. Further, during heat treatment, Ga and N in the semiconductor layer are decomposed and easily vaporized.
Is more likely to evaporate, and the evaporation is controlled by the protective film in the portion with the protective film 8, but N is more easily evaporated in the portion without the protective film 8. From the p-type layer of gallium nitride based compound semiconductor to N
Evaporates to become n-type, resulting in high resistance. As a result, the resistance of the current non-injection region without the protective film 8 can be increased. The protective film 8 described above is formed by depositing SiO ₂ or the like on the entire surface by a CVD method, a sputtering method, or the like and performing only a photolithography process such as exposure, development, or etching of the resist film so that only the surface of the current injection region is exposed. The protective film 8 can be provided only on a necessary portion.

Next, the protective film 8 is removed, a resist film is provided, and reactive ion etching is performed in a chlorine gas atmosphere to etch a part of the stacked semiconductor layers to expose the high temperature buffer layer 3, A p-side electrode 9 made of Au or the like is provided on the surface of the current injection region on the contact layer 7, and an n-side electrode 10 made of Al or the like is provided on the surface of the high temperature buffer layer 3 exposed by etching, and the semiconductor laser chip is obtained by dicing. (See FIG. 1C).

If the resistance of the current non-injection region is completely increased, the electrode patterning is unnecessary and the p-side electrode can be provided on the entire surface of the contact layer 7.

Example 2 In this example, after the epitaxial growth of the p-type layer or after the epitaxial growth, heat treatment is performed in an atmosphere containing H such as H ₂ or NH ₃ gas to bond or chip the p-type dopant and H. The resistance of only the electron injection region is reduced by accelerating the evaporation of N in the gallium bromide-based compound semiconductor to increase the resistance and then activating the electron injection region by irradiating it with an electron beam. FIG. 2 is a schematic diagram when electron beams are irradiated only on the current injection region after the semiconductor layers are stacked.

The electron beam irradiation apparatus includes an electron gun 31, an electron beam scanning unit 32, and an electron beam scanning unit 32, as shown in the conceptual diagram of FIG.
Ordinary electron beam irradiation device 3 including an electron beam focusing system 33 and the like
No. 9 can be used, but using an electron beam irradiation device for mask production or wafer direct writing enables irradiation with an accuracy of 1 μm or less, and an annealing process can be accurately performed only in the current injection region. Therefore, it is preferable. An acceleration voltage of about 3 to 30 kV is applied between the electron gun 31 and the electrode holding the sapphire substrate.
The diameter of the electron beam 34 radiated from 1 is converged by the voltage applied to the electron beam converging system 33, and becomes about 1 to 100 μm on the surface of the wafer 36 which is a compound semiconductor layer laminated, Vertical depth 0.1 to 1μ
permeation up to about m (the permeation depth can be further increased by increasing the acceleration voltage), the semiconductor layer locally rises to about 400 to 800 ° C., and Mg, Zn and H
The bond with and is cut, H is released, and activation is performed.
Since this annealing by electron beam irradiation is performed locally, only the current injection region is activated and the resistance becomes low,
The non-injection region of the current can be maintained at a high resistance.

In each of the above embodiments, GaN, Al _x Ga _1-x N, and Ga _y I are used as the gallium nitride-based compound semiconductor.
Although the example of the laminated film of n _{1 -y} N has been described, the semiconductor layer is not limited to the material having the above-described composition, and is generally Al _p Ga _q I.
n _1-pq N (0 ≦ p <1, 0 <q ≦ 1, 0 <p + q ≦
1), for example, p is selected so that the composition ratio is selected so that the bandgap energy of the active layer is smaller than the bandgap energy of the cladding layer.
It is also possible to select q and change the composition amount. In addition, a part or all of N of Al _p Ga _q In _{1 -pq} N is A
The present invention can be similarly applied to a material substituted with s and / or P or the like.

[0035]

According to the method of manufacturing the semiconductor laser of the present invention,
The current injection region can be accurately controlled by simply providing a protective film in a predetermined range and performing heat treatment in an atmosphere containing H, or by irradiating a predetermined range with an electron beam and annealing. A semiconductor laser having a stripe structure in which a current injection region and a non-injection region are accurately divided can be obtained by various processes. As a result, a semiconductor laser having a small leakage current and a high luminous efficiency can be obtained at low cost.

[Brief description of drawings]

FIG. 1 is a process cross-sectional explanatory view of a first embodiment of a method for manufacturing a semiconductor laser of the present invention.

FIG. 2 is a schematic explanatory view showing electron beam irradiation in Example 2 of the method for producing a semiconductor laser of the present invention.

FIG. 3 is a schematic explanatory view of an example of an electron beam irradiation device.

FIG. 4 is a sectional explanatory view showing an example of a structure for controlling a current injection region of a conventional semiconductor laser.

[Explanation of symbols]

 1 substrate 3 high temperature buffer layer 4 n-type clad layer 5 active layer 6 p-type clad layer 7 contact layer 8 protective film 11 electron beam

Claims (5)

[Claims] 1. A laminate of (a) a gallium nitride based compound semiconductor, which comprises at least an n-type layer, an active layer and a p-type layer, and which constitutes a semiconductor laser, on a substrate, and (b) the laminated semiconductor layers. Activate the p-type layer in the current injection region,
(C) A method of manufacturing a semiconductor laser, characterized in that the p-type layer in a region other than the current injection region of the stacked semiconductor layers is maintained in an inactivated state. 2. The laminated semiconductor layers are an n-type buffer layer, an n-type cladding layer, an active layer, a p-type cladding layer and a p-type cladding layer.
The method for producing a semiconductor laser according to claim 1, wherein the method is a contact layer. 3. The p-type layer is activated by heat-treating the entire substrate after the semiconductor layers are laminated, and then a protective film is provided on the surface of the current injection region and heat-treated in an atmosphere containing hydrogen. 3. The method for producing a semiconductor laser according to claim 1, wherein the regions other than the current injection region are thereby inactivated. 4. The method for manufacturing a semiconductor laser according to claim 3, wherein the heat treatment for activating the p-type layer is performed at 400 to 800 ° C. in a nitrogen atmosphere. 5. The method of manufacturing a semiconductor laser according to claim 1, wherein after the semiconductor layers are stacked, only the current injection region is irradiated with an electron beam to activate only the current injection region of the p-type layer.