JPH11238912A - Light-emitting diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light emitting diode providing high emission power, having a p-n junction composed of an Si-doped n-type GaAlAs epitaxial layer and Si-doped p-type GaAlAs epitaxial layer. SOLUTION: Cleaning of a substrate and polycrystal with a high-purity chemical and pure water, refining of a gas to be used as an atmosphere gas and purification of an apparatus for growing are performed thoroughly to avoid an unwanted S impurity from mixing in Si-doped GaAlAs epitaxial layers to reduce the S concn. in the Si-doped GaAlAs epitaxial layer to 3×10<16> cm<-3> or lower.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an infrared light emitting diode made of GaAlAs, and more particularly to a GaAlAs infrared light emitting diode having an improved light emission output.

[0002]

2. Description of the Related Art An epitaxial wafer in which a pn junction is formed by a Si-doped n-type GaAlAs epitaxial layer and a Si-doped p-type GaAlAs epitaxial layer,
It is widely used as a material for infrared light emitting diodes (LEDs) used as photocouplers, various optical sensors, light sources for remote controllers, and the like.

A light emitting diode manufactured by using the above-mentioned epitaxial wafer includes, for example, Journal.
of Applied Pyhsics, Vol. 4
8, No. 6 (1977), pages 2485 to 2492, a light emitting diode having the structure shown in FIG. 1 is known. In FIG. 1, reference numeral 1 denotes a Si-doped n-type GaAlAs
The epitaxial layer, 2 is a Si-doped p-type GaAlAs epitaxial layer, 3 is an n-electrode, and 4 is a p-electrode. Light emitted from the pn junction is extracted from the surface of the n-type GaAlAs layer 1 on which the n-electrode 3 is formed.

In general, the pn junction of the light emitting diode is formed by using np natural inversion of Si, which is an amphoteric impurity.
It is manufactured continuously by a liquid phase epitaxial growth method.
That is, in the liquid phase epitaxial growth of a GaAlAs layer to which Si is added as an impurity, since Si is an amphoteric impurity, the epitaxial layer grown at a temperature higher than the inversion temperature becomes an n-type and the epitaxial layer grown at a temperature lower than the inversion temperature. Becomes p-type. Therefore, when the GaAlAs layer is liquid-phase epitaxially grown on the GaAs substrate by using the Si as a dopant from a temperature higher than the inversion temperature to a lower temperature by the slow cooling method, the n-type layer and the p-type layer can be continuously grown. Therefore, GaAs doped with Si using the liquid phase epitaxial growth method of the above-described slow cooling method is used.
When an lAs epitaxial wafer is manufactured, high quality p
There is an advantage that the formation of the n-junction is easy and the productivity is high.

However, in the liquid phase epitaxial growth of GaAlAs, since the segregation coefficient of AlAs to the solid phase is significantly larger than 1, the AlAs mixed crystal ratio in the epitaxial layer decreases in the growth direction. As a result, in the above case, the band gap of the GaAlAs epitaxial layer becomes smaller toward the surface of the p-type layer.
It becomes difficult to extract light from the surface of the p-type layer. Therefore, in the manufacture of a light emitting diode, the GaAs substrate is removed after the epitaxial layer is grown, and the surface side of the n-type GaAlAs epitaxial layer is used as a light extraction surface.

That is, in the manufacture of a light emitting diode, GaAs of an epitaxial wafer manufactured by the above method is used.
After removing the s substrate by etching or the like and polishing the removed surface as necessary, electrodes are formed on the front and back surfaces of the epitaxial wafer with the removed surface (n-side GaAlAs epitaxial layer surface) as the light extraction side, and the Separate to produce a light emitting diode. By adjusting the Al composition, this light-emitting diode can achieve approximately 80
It can emit infrared light in the range of 0-900 nm.

[0007]

The above-mentioned infrared light emitting diode has been demanded from the market to increase the output of light emission. As a method of increasing the output, for example, Japanese Patent Application Laid-Open No. 4-337680
It has been reported that high output can be obtained by steepening the Al mixed crystal ratio gradient in the light emitting region near the pn junction as described in, but the demands of the market are increasing year by year, and further increase in output is required. It has been demanded. Therefore, the object of the present invention is to
An object of the present invention is to provide a Si-doped GaAlAs infrared light emitting diode having an improved light output.

[0008]

SUMMARY OF THE INVENTION The present invention provides a Si-doped n
-Type GaAlAs epitaxial layer and Si-doped p-type Ga
A light emitting diode having a pn junction made of an AlAs epitaxial layer, wherein the Si-doped n-type GaAlA
s epitaxial layer and Si-doped p-type GaAlAs
The sulfur (S) concentration in the epitaxial layer is 3 × 10
It is characterized by being ¹⁶ cm ^-3 or less. In the above light emitting diode, the sulfur (S) concentration in each of the Si-doped n-type GaAlAs epitaxial layer and the Si-doped p-type GaAlAs epitaxial layer is 1 × 10 ¹⁶ c
More preferably, it is not more than m ^-3 .

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have paid attention to the phenomenon in which the above-mentioned Si-doped GaAlAs infrared light emitting diode has a variation in light emission output depending on the production lot even when produced by the same production process. As a result of a detailed investigation on the relationship between various physical properties of the light emitting diode and the light emission output, it was found that there was a negative correlation between the concentration of sulfur (S) as an impurity contained in the GaAlAs epitaxial layer and the light emission output. .

Although S is not intentionally added to the epitaxial layer, it is considered that S is mixed into the growth apparatus during the liquid phase epitaxial growth in some form. GaAl
In the liquid phase epitaxial growth of the As layer, S is GaAs.
Since the segregation coefficient with respect to the lAs layer is very large, even if a small amount of S source exists in the system of the growth apparatus, GaAlAs
The S concentration in the layer increases.

Then, the present inventors investigated the cause of the contamination of S into the system of the growth apparatus. As a result, it was found that the raw material, the atmosphere gas, and the growth apparatus used for the epitaxial growth were sources of S contamination. Therefore, the present inventors have taken measures to reduce the S concentration in the raw materials and the atmosphere gas used for the epitaxial growth and the growth apparatus. That is, a GaAs single crystal substrate and GaAs used for epitaxial growth.
If a sulfuric acid-based etchant is used in the pretreatment before the use of polycrystal, it is also a source of S. Therefore, after performing etch treatment by adjusting the etchant using a high-purity chemical, it is sufficiently washed with ultrapure water. Then, processing such as ultrasonic cleaning was performed as needed. The atmosphere gas such as hydrogen or argon which forms the atmosphere for the epitaxial growth is purified from commercially available high-purity gas using a purifier before use, and supplied to a reaction furnace. In addition, as for the graphite used as the material of the epitaxial growth apparatus, a high-purity graphite is used, and further, before being actually used for the epitaxial growth, baking is performed at a high temperature of about 1400 ° C., for example, in a hydrogen chloride gas atmosphere to purify. It was to be.

Conventionally, the S concentration in a GaAlAs epitaxial layer has been about 5 × 10 ¹⁶ cm ⁻³ or more. On the other hand, the present inventors have thoroughly carried out the above-described method, and have found that the Si-doped n-type GaAlAs epitaxial layer and the Si-doped p-type GaAlAs epitaxial layer
The concentration is 3 × 10 ¹⁶ cm ⁻³ or less, more preferably 1 × 10 ¹⁶ cm ⁻³ or less.
It is possible for the first time to control the pressure to 10 ¹⁶ cm ^-3 or less. By controlling the S concentration in the GaAlAs epitaxial layer to 3 × 10 ¹⁶ cm ⁻³ or less, the GaAs
The output of the 1As infrared light emitting diode could be increased as compared with the conventional one.

FIG. 2 shows a conventional light-emitting diode and a light-emitting diode obtained according to the present invention, in which Si-doped GaAlAs is used.
4 shows the relationship between the S concentration in a layer and the light emission output. In Fig. 2, black circles ●
Is a light-emitting diode in which the S concentration in the Si-doped GaAlAs epitaxial layer according to the present invention is 3 × 10 ¹⁶ cm ⁻³ or less, and a white circle indicates a conventional Si-doped GaAlAs.
S concentration in the epitaxial layer is about 5 × 10 ¹⁶ cm ⁻³
The above is the light emitting diode. As shown in FIG. 2, the output is almost constant for a light emitting diode having an S concentration in the epitaxial layer of 1 × 10 ¹⁶ cm ⁻³ or less, but 1 × 10 ¹⁶ c
When it became higher than m ^-3 , the output began to decrease. Then, it was found that when the S concentration in the epitaxial layer was higher than 3 × 10 ¹⁶ cm ⁻³ , the output sharply decreased. Therefore, S
When the S concentration in the i-doped GaAlAs layer is 3 × 10 ¹⁶ cm ⁻³
In the following, it was found that the light-emitting diode has a high output by more preferably 1 × 10 ¹⁶ cm ⁻³ or less.

The Si-doped n-type Ga according to the present invention
AlAs epitaxial layer and Si-doped p-type GaAlA
For a method of manufacturing an epitaxial wafer used for a light emitting diode having a pn junction composed of an s epitaxial layer, a method in which a GaAs substrate is doped with Si as a dopant and a GaAl
A method for continuously growing a liquid phase epitaxially on an As layer by a slow cooling method has been described. However, the method of manufacturing the epitaxial wafer is not limited to the above method. For example, after growing an n-type GaAlAs layer on a GaAs substrate at a temperature higher than the np inversion temperature, the substrate and the growth solution are separated and the growth is performed. After the temperature of the solution for cooling is lowered to the np inversion temperature or lower, the substrate and the solution for growth are brought into contact again to form p-type Ga.
The effects of the present invention can be obtained even when an epitaxial wafer is manufactured by a liquid phase epitaxial growth method for growing an AlAs layer. Even in this case, the sulfur (S) concentration in both the Si-doped n-type GaAlAs epitaxial layer and the Si-doped p-type GaAlAs epitaxial layer can be reduced to 3 × 10 5 by reducing the amount of S sources mixed into the system of the epitaxial growth apparatus by the above-described method. ^{It can be 16} cm ⁻³ or less, more preferably 1 × 10 ¹⁶ cm ⁻³ or less.

[0015]

According to the present invention, the sulfur (S) concentration in both the Si-doped n-type GaAlAs epitaxial layer and the Si-doped p-type GaAlAs epitaxial layer is set to 3 × 10 ¹⁶ cm ^-3.
The output of the light emitting diode can be improved by setting the value to 1 × 10 ¹⁶ cm ⁻³ or less, more preferably. Regarding the reason that there is a correlation between the S concentration in the epitaxial layer and the light emission output, it seems that S taken into the crystal during the liquid phase epitaxial growth is involved in the formation of the non-light emitting center, Details are unknown.

[0016]

EXAMPLE An example in which a light emitting diode of the present invention is manufactured using an epitaxial wafer manufactured by a liquid phase epitaxial growth method of a slow cooling method using a slide boat type growth apparatus will be described. FIG. 3 shows a slide boat type growth apparatus used in this embodiment. In FIG.
Is a boat for storing substrates, 22 is a recess for storing substrates, 23
Is a n-type GaAs single crystal substrate, 24 is a slider containing a Ga solution, 25 is a solution reservoir, 26 is a Ga solution, 27 is a small hole, and 28 is a lid.

As a raw material for growing a Si-doped GaAlAs epitaxial layer, a Ga solution, Ga
Predetermined amounts of As polycrystal, Al and Si were added. N-type GaAs having a (100) plane in the recess 22 for accommodating the substrate.
The s single crystal substrate 23 was set. Then, in a state where the GaAs single crystal substrate 23 and the Ga solution 26 were not brought into contact with each other, the growth apparatus in which both were set was placed in a quartz glass reaction tube (not shown).

Subsequently, the heater around the reaction tube was heated to raise the temperature of the growth apparatus to 940 ° C. in a stream of hydrogen, and maintained at the same temperature for 2 hours. During this time, GaAs polycrystal, Al, S
i was uniformly dissolved in the Ga solution. Thereafter, the slider 24 containing the Ga solution is slid to slide the Ga solution 26 and the n-type G
The slider 24 was slid to a position where the small hole 27 came on the GaAs single crystal substrate 23, and a Ga solution having a predetermined thickness was placed on the GaAs single crystal substrate. In this state, the growth apparatus is cooled to 600 ° C. at a cooling rate of 0.4 ° C./min, and utilizing the natural inversion of Si,
n-type GaAlAs epitaxial layer and p-type GaAlAs
An epitaxial layer was continuously grown. The spontaneous inversion temperature of Si is approximately 830 ° C.

In the above-mentioned epitaxial growth of the GaAlAs layer, all means for reducing the S concentration in the GaAlAs layer described above were implemented. That is, cleaning of the substrate and the polycrystal with a high-purity chemical and pure water, purification of the gas used as the atmospheric gas, and purification of the growth apparatus were all performed.

The thickness of the GaAlAs epitaxial wafer obtained as described above was 100 μm for the n-type GaAlAs epitaxial layer and 200 μm for the p-type GaAlAs epitaxial layer. The carrier concentration of the GaAlAs epitaxial layer is n at the interface with the substrate.
It was 1 × 10 ¹⁸ cm ^{−3 for} the mold and 2 × 10 ¹⁸ cm ⁻³ for the p-type on the surface of the epitaxial layer. In order to manufacture a light emitting diode using this epitaxial wafer, the epitaxial wafer was first immersed in an ammonia-based etchant, and the GaAs single crystal substrate was removed. Thereafter, electrodes were formed on the surface of the p-type epitaxial layer and the surface of the n-type epitaxial layer, respectively, and separated into substantially square devices having a side of about 350 μm. The obtained light emitting diode has the structure shown in FIG. GaAlA obtained by this embodiment
The S concentration in the epitaxial layer of the s-infrared light emitting diode was 0.5 to 3 × 10 ¹⁶ cm ⁻³ .

(Comparative Example) A GaAlAs light emitting diode was manufactured in the same manner as in the above embodiment. However, in the growth of the GaAlAs epitaxial layer according to the present comparative example, the above-described means for reducing the S concentration in the epitaxial layer was not particularly performed as in the related art. The S concentration in the epitaxial layer of the Si-doped GaAlAs light-emitting diode obtained by this comparative example is approximately 5 to 10 × 10 ¹⁶ c
m ^-3 .

Table 1 shows the results of measuring the luminous output of each of the 100 light-emitting diodes produced in the above example and comparative example. As is clear from Table 1, according to the present invention, a light emitting diode having a light emitting output approximately three times higher than that of a conventional product was obtained.

[0023]

[Table 1]

[0024]

According to the present invention, Si-doped n-type GaAs is provided.
lAs epitaxial layer and Si-doped p-type GaAl
Both the S concentration in the As epitaxial layer is 3 × 10 ¹⁶ c
By controlling the concentration to not more than m ⁻³ , more preferably not more than 1 × 10 ¹⁶ cm ⁻³ , the conventional S concentration is about 5 to 10 × 10
The light emitting output of the light emitting diode could be improved about three times as compared with the GaAlAs infrared light emitting diode of about ¹⁶ cm ^-3 . In the above embodiment, the n-type GaAlAs epitaxial layer forming the pn junction and the p-type GaAlAs
Although the case of the light emitting diode having a structure including two epitaxial layers has been described, the same applies to a light emitting diode having a structure in which a window layer made of a p-type GaAlAs layer is further formed on the above two layers forming a pn junction. The effect of the present invention can be obtained. In the above description of the present invention, the light emitting diode according to the present invention is a Si-doped n-type GaAl
Although only the case where the surface side of the As epitaxial layer is the light extraction surface has been described, the surface side of the p-type epitaxial layer is defined as the light extraction surface as in the light emitting diode having the window layer formed of the p-type GaAlAs layer. If possible, the light emitting diode according to the present invention can use the surface side of the p-type epitaxial layer as a light extraction surface.

[Brief description of the drawings]

FIG. 1 is a diagram showing a structure of a Si-doped GaAlAs infrared light emitting diode.

FIG. 2 is a diagram showing the relationship between the S concentration in the epitaxial layer of the Si-doped GaAlAs infrared light emitting diode and the light emission output.

FIG. 3 is a diagram showing a liquid phase epitaxial growth apparatus.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 Si-doped n-type GaAlAs epitaxial layer 2 Si-doped p-type GaAlAs epitaxial layer 3 n-electrode 4 p-electrode 21 substrate storage boat 22 substrate recess 23 n-type GaAs single crystal substrate 24 slider containing Ga solution 25 solution reservoir 26 Ga solution 27 Small hole 28 Lid

Claims (2)

[Claims] In a light emitting diode having a pn junction comprising a Si-doped n-type GaAlAs epitaxial layer and a Si-doped p-type GaAlAs epitaxial layer, sulfur (Si) in the Si-doped n-type GaAlAs epitaxial layer and the Si-doped p-type GaAlAs epitaxial layer is S) A light-emitting diode having a concentration of 3 × 10 ¹⁶ cm ⁻³ or less. 2. The sulfur (S) concentration in each of the Si-doped n-type GaAlAs epitaxial layer and the Si-doped p-type GaAlAs epitaxial layer is 1 × 10 ¹⁶ cm ^−3.
The light emitting diode according to claim 1, wherein: