JPH11274557A - Method for manufacturing p-type gallium nitride-based compound semiconductor layer - Google Patents

Abstract

(57) Abstract: A p-type GaN layer formed on an n-type GaN layer can be reduced in resistance by annealing, and deterioration of the n-type GaN layer during annealing can be prevented. A low-resistance p-type Ga is formed on an n-type GaN layer.
In the method for manufacturing the N layer 14, the sapphire substrate 11
On top of the GaN buffer layer 12 by MOCVD,
A doped n-type GaN layer 13 is grown and then n-type GaN
A Mg-doped p-type GaN layer 14 is grown on the layer 13, and then irradiated with a nitrogen laser having a wavelength of 337 nm while flowing nitrogen gas under a reduced pressure of 300 Pascal.
Anneal at 30 ° C. for 30 minutes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for manufacturing a light emitting device such as an ultraviolet / blue light emitting diode and an ultraviolet / blue laser diode, and more particularly to a method for forming a p-type gallium nitride based compound semiconductor layer by a vapor phase growth method. And a method for producing a p-type gallium nitride-based compound semiconductor layer.

[0002]

2. Description of the Related Art Many studies have been made on ZnSe, SiC, GaN and the like as semiconductor materials for blue light emitting devices. Among them, recently, a gallium nitride-based compound semiconductor layer (Ga _x Al ₁ -xN (0 ≦ x ≦ 1))
Has attracted attention as exhibiting strong blue light emission at room temperature (Japanese Patent Laid-Open No. 5-183189).

The main method of growing a gallium nitride-based compound semiconductor layer is metal organic chemical vapor deposition (MOCVD) using trimethyl gallium (TMG), trimethyl aluminum (TMA), ammonia or the like as a source gas.
Method) is used. Si as a donor impurity and Zn, Cd, Be, Mg, C as an acceptor impurity
a, Ba, etc. are used. At this time, since there is no good substrate that lattice-matches the gallium nitride-based compound semiconductor layer, AlN, G
After growing a buffer layer made of aN or the like, the temperature is increased to 900
The temperature is raised to about 1100 ° C., and an n-type layer and a p-type layer are sequentially laminated to form a light emitting device.

However, even if an attempt is made to grow a low-resistance p-type layer by doping the acceptor impurity at a high concentration, the acceptor cannot be activated unless some process is added after the growth, so that only the i-layer having a specific resistance of 10 ⁸ Ωcm or more is used. Could not be obtained. It is considered that the reason for this is that during the growth by MOCVD, hydrogen enters into the crystal from the reaction gas or atmospheric gas, and inactivates the acceptor impurities.

[0005] Therefore, the atmosphere is vacuum or N ₂ , H
e, Ar alone or in a mixed gas thereof, 400
It has been practiced to lower the resistance of a p-type gallium nitride-based semiconductor layer by annealing at a temperature of not less than ° C and evaporating hydrogen from the crystal (Japanese Patent Application Laid-Open No. 5-183189).

However, when a light emitting device substrate having a pn junction is annealed by the above-described method, the temperature rises to the n-type gallium nitride-based compound semiconductor layer which does not originally need to be annealed, so that the n-type layer is deteriorated. Occurs. That is, when the temperature is relatively high, N is evaporated from the n-type layer, and a non-emission center including N vacancies is generated. For this reason, the internal quantum efficiency of the n-type layer is reduced, and the characteristics as a light emitting device are significantly deteriorated.

When the temperature is relatively low, the evaporation of hydrogen in the p-type crystal, which causes the increase in resistance, from the crystal surface does not progress so much, and the time required for reducing the resistance is low. , The resistance of the p-type layer near the pn junction far from the surface is not completely reduced. For this reason,
The efficiency of hole injection into the n-type layer decreases, and the characteristics of the light emitting device deteriorate.

[0008]

As described above, conventionally, in the production of a blue light emitting device or the like, in order to lower the resistance of a p-type gallium nitride-based compound semiconductor layer, annealing at a temperature exceeding 400 ° C. It is necessary to evaporate hydrogen from the inside, but at such a temperature, there is a problem that the underlying n-type gallium nitride-based compound semiconductor layer is deteriorated.

The present invention has been made in consideration of the above circumstances, and has as its object to reduce the number of lower n layers during annealing.
For manufacturing a p-type gallium nitride-based compound semiconductor layer capable of reducing the resistance of a p-type gallium nitride-based compound semiconductor layer uniformly in the thickness direction in a short time without causing deterioration of the p-type gallium nitride-based compound semiconductor layer Is to do.

[0010]

(Structure) In order to solve the above-mentioned problem, the present invention employs the following structure.
That is, the present invention provides a method for producing a p-type gallium nitride-based compound semiconductor layer, comprising the steps of: growing a p-type impurity-doped gallium nitride-based compound semiconductor layer on the n-type gallium nitride-based compound semiconductor layer by a vapor phase growth method; Irradiating the grown gallium nitride-based compound semiconductor layer with light having an energy equal to or greater than the forbidden band width of the semiconductor layer under a reduced pressure of 20 to 1000 Pascal while flowing a nitrogen gas; And annealing at a temperature of

Here, preferred embodiments of the present invention include the following. (1) Before annealing the gallium nitride-based compound semiconductor layer grown on the n-type gallium nitride-based compound semiconductor layer together with light irradiation, a cap layer that is substantially transparent to light is formed on the semiconductor layer. thing. (2) As a gallium nitride based compound semiconductor layer, Ga _x Al
_{Use 1-x} N (0 ≦ x ≦ 1). (3) The MOCVD method is used as the vapor phase growth method.

(Function) In the present invention, p
After growing the gallium nitride-based compound semiconductor layer doped with the p-type impurities, light of energy equal to or larger than the forbidden band width of the grown gallium nitride-based compound semiconductor layer is applied to the semiconductor under a reduced pressure of 20 to 1000 Pascal while flowing nitrogen gas. Annealing is performed at a temperature of 200 to 400 ° C. while irradiating the layer.

Here, when the pressure of the nitrogen gas is lower than 20 Pascal, the evaporation of N from the gallium nitride-based compound semiconductor layer cannot be prevented, and when it is higher than 1000 Pascal, the evaporation of hydrogen is suppressed. Is desirable. This method can prevent the evaporation of nitrogen from the crystal and accelerate the evaporation of hydrogen from the crystal.

In the present invention, the reason why the semiconductor is irradiated with light having energy equal to or larger than the forbidden band width of the p-type gallium nitride-based compound semiconductor layer at the time of annealing is to apply light energy only to the p-type layer. Thermal energy selectively applied only to the p-type layer recombine at the crystal defects, thereby helping the released phonons to migrate hydrogen out of the crystal and evaporate out.

The reason why the annealing temperature is set to 200 to 400 ° C. is that if the temperature is lower than 200 ° C., the evaporation of hydrogen does not occur, and the resistance does not decrease. This is because an element harmful to lowering the resistance, such as sodium, adheres to the GaN surface.

In the present invention, decomposition and evaporation of nitrogen from the gallium nitride-based compound semiconductor layer can be sufficiently prevented, but a cap which is substantially transparent to light on the p-type gallium nitride-based compound semiconductor layer is provided. By providing the layer, it is possible to further prevent the evaporation of nitrogen from the gallium nitride-based compound semiconductor layer.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the illustrated embodiments. FIG. 1 is a sectional view showing a laminated structure of a gallium nitride-based compound semiconductor to which a method according to an embodiment of the present invention is applied.

First, on a sapphire substrate 11 housed in a CVD chamber, a Si-doped n-type GaN layer 13 is grown to a thickness of 20 μm via a GaN buffer layer 12 by MOCVD using TMG, TMA, and ammonia as source gases. Further, an Mg-doped p-type GaN layer 14 is further
It grew to 0 μm. This wafer was divided into two parts, one of which was a wavelength of 337 nm and an energy density of 2000 W / cm.
While irradiating the nitrogen laser of Step ² and flowing nitrogen, 300
Annealing was performed at 350 ° C. for 30 minutes under a reduced pressure of Pascal. In the other, while flowing nitrogen at normal pressure, 80
Annealing was performed at 0 ° C. for 15 minutes.

After taking out both wafers from the CVD chamber, electrodes were attached and light emitting diodes were formed. FIG. 2 shows the emission spectra of both at a driving current of 30 mA.
The solid line 1 is the former sample, and the broken line 2 is the latter sample. The band-edge emission of the former was very strong, but the band-edge emission of the latter was weak, and light emission due to a deep order was observed. When annealing the former wafer, p-type Ga
A cap layer made of SiO _{2 is formed} on the N layer 14 to a thickness of 100 nm.
When attached, the band edge emission was stronger than that without.

As described above, according to this embodiment, the p-type Ga
When the N layer 14 is annealed, by irradiating light and optimizing the pressure of the nitrogen gas and the annealing temperature, the p-type GaN layer 1 is not deteriorated without deteriorating the n-type GaN layer 13.
4 can be uniformly reduced in the thickness direction in a short time. Further, thermal energy can be intensively applied only to the p-type GaN layer 14, and the annealing temperature can be lowered. In addition, a crystal in which the stoichiometric ratio of the group III to the group V is 1: 1 can be obtained. Therefore, it is extremely effective for manufacturing not only light emitting diodes but also blue light emitting devices.

By providing a cap layer on the p-type GaN layer 14 that is transparent to the irradiation light during annealing,
It is possible to further prevent the evaporation of N from the GaN layers 13 and 14.

The present invention is not limited to the above embodiment. In the embodiment, the manufacture of GaN has been described. However, the present invention is not limited to this, and can be applied to GaAlN, and can be applied to the manufacture of various gallium nitride-based compound semiconductors.

The pressure of the nitrogen gas during annealing is 3
The pressure is not limited to about 00 Pascal but may be any pressure reduction condition that prevents evaporation of nitrogen from the crystal and accelerates evaporation of hydrogen from the crystal. Specifically, if the pressure of the nitrogen gas is lower than 20 Pascal, the evaporation of N from the gallium nitride-based compound semiconductor layer cannot be prevented. Further, when the pressure of the nitrogen gas is higher than 1000 Pascal, the evaporation of hydrogen is suppressed.

Further, in the present invention, the light irradiated at the time of annealing only needs to be sufficiently absorbed by the p-type gallium nitride-based compound semiconductor layer, and has a wavelength having energy equal to or larger than the forbidden band width of the semiconductor layer. Good.

The annealing temperature is not limited to about 350.degree. C. but can be changed as appropriate according to the specifications. However, if the annealing temperature is lower than 200 ° C., the evaporation of hydrogen does not occur and the resistance does not decrease, so that the annealing temperature is preferably 200 ° C. or higher. Further, if the annealing temperature exceeds 400 ° C., elements harmful to lowering the resistance, such as carbon and sodium, adhere to the surface of the gallium nitride-based compound semiconductor layer. Therefore, the annealing temperature is preferably 400 ° C. or lower. In addition, various modifications can be made without departing from the scope of the present invention.

[0026]

As described above in detail, according to the present invention, after growing a gallium nitride-based compound semiconductor doped with a p-type impurity on an n-type gallium nitride-based compound semiconductor layer by a vapor phase growth method, 20 to 1000 while flowing
Preventing nitrogen from evaporating from the crystal by annealing at a temperature of 200 to 400 ° C. while irradiating the semiconductor with light having energy equal to or larger than the forbidden band width of the p-type gallium nitride based compound semiconductor under reduced pressure of Pascal At the same time, the evaporation of hydrogen can be accelerated, so that the n-type layer does not deteriorate during annealing, and the resistance of the p-type gallium nitride-based compound semiconductor is reduced uniformly in the thickness direction in a short time. Becomes possible.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a semiconductor structure created in an embodiment.

FIG. 2 is a diagram showing an emission spectrum of a gallium nitride-based light emitting diode in an embodiment in comparison with a conventional example.

[Explanation of symbols]

11 sapphire substrate 12 GaN buffer layer 13 n-type GaN layer (n-type gallium nitride-based compound semiconductor layer) 14 p-type GaN layer (p-type gallium nitride-based compound semiconductor layer)

Claims (2)

[Claims] A step of growing a gallium nitride-based compound semiconductor layer doped with a p-type impurity on the n-type gallium nitride-based compound semiconductor layer by a vapor phase growth method, and under a reduced pressure of 20 to 1000 Pascal while flowing a nitrogen gas. While irradiating the grown gallium nitride-based compound semiconductor layer with light having an energy equal to or greater than the forbidden band width of the semiconductor layer,
Annealing at a temperature of 00 to 400 ° C., the method for manufacturing a p-type gallium nitride-based compound semiconductor layer. 2. The method according to claim 1, wherein a cap layer substantially transparent to the light is formed on the gallium nitride-based compound semiconductor layer before annealing the grown gallium nitride-based compound semiconductor layer. The method for producing a p-type gallium nitride-based compound semiconductor layer described above.