JP4137223B2 - Method for producing compound semiconductor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a compound semiconductor used for a light emitting diode, a laser diode, or the like, and more particularly to a method of manufacturing a compound semiconductor capable of reducing the resistance of a GaN-based compound semiconductor doped with a P-type impurity.
[0002]
[Prior art]
GaN-based compound semiconductors are used for blue light-emitting diodes, which have long been a concern. In general, a light emitting diode is configured by pn-junction of an N-type semiconductor and a P-type semiconductor manufactured by a method such as a gas phase or a liquid phase.
Recently, light emitting diodes having excellent light emission efficiency have been implemented with a light emitting layer sandwiched between PN junctions having a single quantum well structure, a multiple quantum well structure, or the like. Such a light emitting diode with excellent luminous efficiency requires a more excellent N-type semiconductor or P-type semiconductor.
[0003]
For example, there are the following methods for manufacturing a P-type semiconductor.
First, as disclosed in JP-A-2-257679, a method of obtaining a P-type crystal by irradiating an electron beam after doping a GaN-based compound semiconductor with a P-type impurity such as Mg and Zn (hereinafter referred to as “P-type crystal”) First method).
Further, as disclosed in JP-A-5-183189, after doping a GaN-based compound semiconductor with P-type impurities such as Mg and Zn, the P-type crystal is annealed at a certain high temperature in a nitrogen atmosphere. There is a method of obtaining (hereinafter referred to as a second method).
[0004]
[Problems to be solved by the invention]
However, in the first method described above, since the penetration depth of the electron beam is shallow, only the pole surface can be reduced in resistance, and it takes a long time to irradiate the entire wafer surface while scanning the electron beam. There is a problem of lack of mass productivity.
The second method is superior in mass productivity to the first method, but the annealing temperature is relatively high (about 400 ° C. to 1000 ° C.), so that the surface of the semiconductor deteriorates during annealing. There is a fear. In order to prevent such a risk, it is necessary to form a protective film (cap layer) on the surface of the semiconductor, and there is a problem that a process for forming the protective film is required. Furthermore, in order to improve the reproducibility of the P-type crystal, it was necessary to anneal at a high temperature of 600 ° C. or higher. In addition, since it is necessary to perform annealing in a nitrogen atmosphere, an apparatus corresponding to the annealing is required.
[0005]
The present invention was devised in view of the above circumstances, and provides a method for producing a compound semiconductor excellent in mass productivity, and a method for producing a compound semiconductor excellent in reproducibility, which may be annealed at a relatively low temperature. The purpose is that.
[0006]
[Means for Solving the Problems]
The method for producing a compound semiconductor according to the present invention includes a step of forming a GaN-based compound semiconductor layer doped with a P-type impurity by vapor deposition, and a growth of the GaN-based compound semiconductor layer on the surface of the GaN-based compound semiconductor layer. A step of forming a thin film of In or InN at a temperature lower than the temperature, and a step of annealing in an atmosphere containing 300 to 800 ° C. and containing O ₂ .
[0007]
In addition, another method for producing a compound semiconductor according to the present invention includes a step of forming a GaN-based compound semiconductor layer doped with a P-type impurity by vapor deposition, and a GaN-based compound on a surface of the GaN-based compound semiconductor layer. Forming a thin film of In or InN at a temperature lower than the growth temperature of the semiconductor layer; removing the thin film of In or InN while leaving a slight amount on the surface of the GaN-based compound semiconductor layer; And annealing in an atmosphere containing O ₂ .
[0008]
Furthermore, the atmosphere containing O ₂ is in the air.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a graph showing the relationship between the annealing temperature and the resistivity in the method for manufacturing a compound semiconductor according to the embodiment of the present invention.
[0010]
The method for manufacturing a compound semiconductor according to an embodiment of the present invention includes a step of forming a GaN-based compound semiconductor layer doped with a P-type impurity by vapor deposition, and a GaN-based compound on a surface of the GaN-based compound semiconductor layer. A step of forming a thin film of In or InN at a temperature lower than the growth temperature of the semiconductor layer, and a step of annealing at an ambient temperature of 300 ° C. or higher and 800 ° C. or lower.
[0011]
First, thermal cleaning is performed by heating the sapphire substrate in a reduced pressure MOCVD apparatus (metal organic vapor phase epitaxy apparatus) at a substrate temperature of 1050 ° C. in a hydrogen atmosphere for about 10 minutes.
[0012]
Next, the substrate temperature of the sapphire substrate is lowered to 520 ° C., nitrogen or hydrogen gas is used as a carrier gas, ammonia gas as an N source is supplied at 11.5 liter / min, and trimethylgallium as a Ga source is supplied. Supplying at 125 μmol / min, a GaN-based compound semiconductor layer as a low-temperature GaN buffer layer is formed on the surface of the sapphire substrate.
[0013]
Furthermore, the substrate temperature of the sapphire substrate was raised to 1020 ° C., and 0.95 μmol / min obtained by adding organomagnesium (biscyclopentadienylmagnesium) to magnesium as a P-type dopant in addition to the ammonia gas and trimethylgallium. The GaN compound semiconductor layer on the surface of the sapphire substrate is doped with magnesium and grown to a thickness of 0.5 μm.
[0014]
The substrate temperature of the sapphire substrate on which Mg-doped GaN is formed as the P-type GaN-based compound semiconductor layer is lowered to 520 ° C., and in this state, trimethylindium as an In source is supplied, and the surface of the GaN-based compound semiconductor layer Then, an In thin film is formed. The In thin film has a thickness of 100 mm. The step of forming the In thin film is performed at a temperature lower than the temperature at which the GaN-based compound semiconductor layer is formed.
[0015]
Next, the sapphire substrate on which the GaN-based compound semiconductor layer and the In thin film are formed is taken out from the low pressure MOCVD apparatus and annealed in an air atmosphere, that is, in an oxygen-containing atmosphere using a general hot plate or sintering furnace. I do.
[0016]
Here, the annealing time was changed to 2, 10, and 30 minutes, and the annealing temperature was changed as appropriate. Then, as shown in FIG. 1, regardless of the annealing time, when the annealing temperature exceeded 300 ° C., the resistivity decreased rapidly. In particular, by performing annealing for 30 minutes at a relatively low temperature of less than 400 ° C., a P-type GaN compound semiconductor having a resistivity of 2 to 4 Ω · cm could be obtained. If the temperature during annealing was set to 500 ° C., an excellent P-type GaN compound semiconductor with a resistivity of 2 Ω · cm could be obtained in a short time of 2 minutes.
[0017]
In general, recent studies have revealed that the resistivity of GaN-based compound semiconductors doped with P-type impurities is decreased by annealing for the following reasons. That is, hydrogen mixed during the crystal growth of the semiconductor hinders the activation of the P-type impurity, which causes the resistivity to increase. However, since the hydrogen is separated from the surface of the semiconductor by annealing, As a result of promoting the activation, the resistivity of the GaN-based compound semiconductor is lowered by annealing.
[0018]
Here, the reason why the resistance becomes lower by forming an In thin film remains unclear at this stage, but is considered to be as follows.
That is, it is considered that the thin film of In functions as a kind of catalyst. The reason is that the In thin film on the GaN-based compound semiconductor layer is very thin even if it is as thin as 100 mm, and as will be described later, the same effect can be obtained even if the In thin film is removed by etching. It is. In other words, if there is even a small amount of In on the GaN-based compound semiconductor layer, it is considered that in an atmosphere containing oxygen, In has an effect of releasing hydrogen mixed in the semiconductor to the outside by the action of a catalyst. .
[0019]
In the first embodiment described above, an In thin film is formed on the surface of the GaN-based compound semiconductor layer, but an InN thin film may be used instead of In. In this case, Mg-doped GaN as a GaN-based compound semiconductor layer is grown on the surface of the sapphire substrate to a thickness of 0.5 μm, and the substrate temperature of the sapphire substrate is lowered to 520 ° C. in the same manner as described above.
[0020]
However, in the compound semiconductor manufacturing method according to the second embodiment, as described above, an InN thin film is formed instead of an In thin film. Therefore, trimethylindium, which is an In source, is supplied at 61 μmol / min while the substrate temperature is 520 ° C., and ammonia gas as an N source is supplied at a rate of 11.5 liter / min.
[0021]
In this case, when a 100-inch InN thin film was formed, almost the same result as in the above-described embodiment could be obtained. That is, the resistivity when annealed at 380 ° C. for 30 minutes was 4 Ω · cm, and the resistivity when annealed at 500 ° C. for 2 minutes was 2 Ω · cm.
[0022]
In the compound semiconductor manufacturing method according to the above-described two embodiments, that is, the first and second embodiments, annealing is performed in a state where the thin film of In or InN is formed on the GaN-based compound semiconductor layer. However, annealing may be performed after removing the thin film of In or InN as follows.
[0023]
In this case, a sapphire substrate having an In or InN thin film formed on the surface of a GaN-based compound semiconductor layer is dipped in hydrochloric acid, and the surface of the In or InN thin film is removed and washed with pure water. Anneal.
[0024]
For example, as in the method of manufacturing the compound semiconductor according to the first embodiment, when annealing is performed at 380 ° C. for 30 minutes, the resistivity is 4 Ω · cm, and when annealing is performed at 500 ° C. for 2 minutes, resistance is increased. The rate was 2 Ω · cm.
[0025]
This did not change greatly depending on whether the thin film formed on the surface of the GaN-based compound semiconductor layer was In or InN.
[0026]
The reason why the same effect can be obtained even if a thin film of In or the like is removed is that, as described above, since In remains even a little, it acts as a catalyst to release hydrogen mixed in the semiconductor to the outside. This is probably because of this.
[0027]
In the embodiment described above, the sapphire substrate is used as the substrate, but the present invention is not limited to this. For example, SiC may be used as the substrate.
[0028]
【The invention's effect】
The method for producing a compound semiconductor according to claim 1 includes a step of forming a GaN-based compound semiconductor layer doped with a P-type impurity by a vapor deposition method, and a step of forming a GaN-based compound semiconductor layer on the surface of the GaN-based compound semiconductor layer. A step of forming a thin film of In or InN at a temperature lower than the growth temperature, and a step of annealing at an ambient temperature of 300 ° C. to 800 ° C.
[0029]
This method is much more mass-productive than conventional methods. Further, as shown in FIG. 1, since the annealing temperature can be lower than that of the conventional method, it is not necessary to form a protective film as in the conventional method, and there is little deterioration of the semiconductor surface during annealing. That is, the resistivity when the annealing temperature is set to 700 ° C. by the conventional method and that when the annealing temperature is set to 500 ° C. by the method according to the present invention are substantially equal. In particular, when the annealing temperature is set to 500 ° C., a good P-type GaN compound semiconductor can be obtained in only 2 minutes. Moreover, it was confirmed that this method was excellent in reproducibility.
[0030]
According to a second aspect of the present invention, there is provided a compound semiconductor manufacturing method comprising: forming a GaN-based compound semiconductor layer doped with a P-type impurity by vapor deposition; and forming a GaN-based compound semiconductor on the surface of the GaN-based compound semiconductor layer. Forming a thin film of In or InN at a temperature lower than the growth temperature of the layer, removing a slight amount of the In or InN thin film on the surface of the GaN-based compound semiconductor layer, and 300 to 800 ° C. Annealing at the ambient temperature.
[0031]
This method differs from the compound semiconductor manufacturing method according to claim 1 described above in that it includes a step of removing a thin In or InN thin film on the surface of the GaN-based compound semiconductor layer before the annealing step. It is a point. However, even if the In or InN thin film is removed, it is difficult to completely remove In from the surface of the GaN-based compound semiconductor layer , so that a small amount of In remains on the surface of the GaN-based compound semiconductor layer. It is considered that the same effect as that of the method for producing a compound semiconductor according to claim 1 is exhibited by the action of In.
[0032]
Further, if the In or InN thin film is removed before the annealing step, an In oxide film or the like is not formed on the surface by annealing in the air, which is excellent in that the subsequent electrode forming process can be performed smoothly.
[0033]
Furthermore, in the method for manufacturing a compound semiconductor according to claim 3, the atmosphere containing O ₂ is in the air. For this reason, since this annealing can be performed with a general hot plate, a sintering furnace or the like, there is an effect that no special manufacturing equipment or the like is required.
[0034]
According to the method as described above, a P-type GaN-based compound semiconductor with high reproducibility can be easily mass-produced more than before, which can contribute to the realization of a light emitting diode excellent in luminous efficiency.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between annealing temperature and resistivity in a method for manufacturing a compound semiconductor according to an embodiment of the present invention.

Claims (3)

A step of forming a GaN-based compound semiconductor layer doped with a P-type impurity by vapor phase growth; A method of manufacturing a compound semiconductor, comprising: a step of forming; and a step of annealing in an atmosphere containing 300 to 800 ° C. and containing O ₂ . A step of forming a GaN-based compound semiconductor layer doped with a P-type impurity by vapor phase growth; Forming, removing the In or InN thin film slightly on the surface of the GaN-based compound semiconductor layer , and annealing in an atmosphere of 300 ° C. to 800 ° C. and containing O _2. The manufacturing method of the compound semiconductor characterized by comprising. The method for producing a compound semiconductor according to claim 1, wherein the atmosphere containing O ₂ is in the air.

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