JP2883338B2 - Manufacturing method of light emitting diode - Google Patents

Description

The present invention relates to a method for manufacturing a light emitting diode made of gallium aluminum arsenide (GaAlAs).

(Prior Art) As a red light emitting diode (having a peak emission wavelength λp of 660 nm) using GaAlAs, a p-GaAlAs (p-type gallium aluminum arsenide) layer on a p-GaAs (p-type gallium arsenide) substrate and n A single heterojunction type in which a GaAlAs (n-type gallium aluminum arsenide) layer is formed by liquid phase epitaxy is generally commercially available. Although such a device has a high production yield and is inexpensive, the luminance obtained is at most about 500 mcd. Therefore, a device having a double hetero structure having different crystal layers on both sides of the active layer has been developed as a device having higher luminance, and has been commercialized. The structure of the light emitting diode having the double hetero structure includes, for example, the following. That is, p-Ga _1-x Al _x As (1 ≧ x> 0) and p-Ga _1-y Al _y As (1
> Y ≧ 0, y <x), n-Ga _1-z Al _z As (1 ≧ z> 0, z> y), and the GaAs substrate easily absorbs light. Sometimes it is removed. A device that removes the GaAs substrate is 3000 mcd, and a device that does not remove it reaches 1000 mcd.

As described above, the red LED with high brightness has been used not only for indoor use but also for outdoor use such as a sign board. There is a demand for higher brightness in outdoor applications.

(Problems to be Solved by the Invention) In order to further increase the brightness of a light emitting diode having a double hetero structure, it is necessary to optimize the carrier concentration, the Al mixed crystal ratio, the crystallinity, etc. of each growth layer. For the precise control of the growth parameters (temperature, time, melt composition, etc.) for this purpose, technical development as seen in the liquid phase growth of laser diodes has been considerably advanced. In addition, a method of controlling liquid phase growth by controlling arsenic (As) having a high vapor pressure at a growth temperature has been developed, and an epitaxial layer having good crystallinity can be obtained.

However, these techniques are very difficult to mass-produce, and are expensive, and are not suitable for use in large quantities. That is, it has been desired to develop a technology that can be mass-produced and has higher luminance. The present invention has been made in view of the above-described conventional problems, and has as its object to provide a method for manufacturing a high-concentration light-emitting diode that can be mass-produced at a low cost with good yield.

[Configuration of the invention]

(Means for Solving the Problems) The method for manufacturing a light emitting diode according to the present invention is performed at 860 ° C.
Ga: 1 g, GaAs: 35 mg, Al: 2.7 mg, Zn: 2.8 m
g of the first p-type growth solution, and the temperature was lowered to 840 ° C. at a cooling rate of 0.5 ° C./min.
s: 49 mg, Al: 1.35 mg, Zn: 1.5 mg, contacted with the second p-type growth solution for 1 minute at the same cooling rate as above, separated, and immediately Ga: 1 g, GaAs: 35 mg, Al: 2.7 mg , Te: n consisting of 5 μg
The method is characterized by comprising a step of bringing the solution into contact with a mold growth solution, lowering the temperature to 650 ° C. at a cooling rate of 0.5 ° C./min, and then separating and allowing to cool.

(Operation) According to the method for manufacturing a light emitting diode of the present invention, a growth apparatus that requires particularly precise control of growth parameters and complicated and expensive vapor pressure control of As is not required, and a structure excellent in mass productivity can be obtained. A light emitting diode is obtained.

(Example) Hereinafter, an example of a method for manufacturing a light emitting diode according to the present invention will be described with reference to the drawings.

FIG. 1 is a cross-sectional view schematically showing the configuration of an example light-emitting element wafer. In Figure 1, 10 denotes a p-type GaAs substrate, at a layer thickness of 15~20μm formed by sequentially laminating on the first major surface _{p-Ga 1-x Al x} As layer of the first crystal layer 11 (1 ≧ x> 0), thick layer
The p-Ga _1-y Al _y As layer (1) of the second crystal layer 12 has a thickness of 0.5 to 2 μm.
> Y ≧ 0, y <x), n-G of the third crystal layer 13 with a layer thickness of 55 μm
a _1-z Al _z As layer (1 ≧ z> 0, z> y).

The above configuration was determined as follows. The above p-GaAs
A p-Ga _1-x Al _x As layer 11, a p-Ga _1-y Al _y As layer 12, n-
FIG. 2 shows the result of examining the relationship between the layer thickness and the light emission output of the n-GaAlAs layer of the light emitting diode formed by sequentially stacking the Ga _{1 -z} Al _z As layers 13. The light output of this graph is normalized by the light output of a conventional light emitting diode having an n-GaAlAs layer thickness of about 30 μm. As is clear from FIG. 2, it was found that a thicker n-GaAlAs layer provided a higher light output than a thinner n-GaAlAs layer.

Next, the p-GaAlAs substrate / p-GaAlAs / p-GaAlAs / n-Ga
The manufacturing process of a light emitting diode having an AlAs structure will be described. A carbon boat having a first p-type growth solution reservoir, a second p-type growth solution reservoir, and an n-type growth solution reservoir is prepared by using a commonly used liquid phase growth apparatus for compound semiconductors, and the following steps are taken. Perform growth. For example, gallium, gallium arsenide, aluminum and the like in the amounts shown in Table 1 are put into the above-mentioned growth solution reservoirs to form a melt. Table 1 below shows an example of the composition of each growth solution.

According to the temperature schedule shown in FIG. 3, the boat is first set at 860 ° C. in an H ₂ atmosphere to homogenize the solution. Then, at the point A in FIG. 3, the first p-type growth solution and the p-type
The temperature is lowered to 840 ° C. at a cooling rate of 0.5 ° C./minute by contacting with a GaAs substrate. Then, at the point B, the first p-type growth solution is separated from the substrate, immediately brought into contact with the second p-type growth solution, and one minute later, the solution is separated from the substrate. During this time, the cooling rate is maintained at 0.5 ° C./min. A thin active layer, which is a light emitting layer, is formed by the second p-type growth solution. Immediately thereafter, the substrate is brought into contact with the n-type growth solution, and the temperature is lowered to 650 ° C. at −0.5 ° C./min.

By the above process, a layer thickness of about 15 is formed on the p-type GaAs substrate.
~ 20 μm p-Ga _1-x Al _x As layer (x is 0.65 to 0.8), 0.5 to
2 μm p-Ga _1-y Al _y As layer (y is approximately 0.36) and n-Ga _1-z Al _z As layer having a thickness of approximately 55 μm (z is 0.6 to 0.8)
Are formed to form a light emitting diode wafer.

In the light emitting diode obtained as described above, when the layer thickness of the n-GaAlAs layer, which is the uppermost layer, is set to 50 μm or more, the light output is increased about 1.5 times that of the conventional light emitting diode. Thus n
-It is not always clear why the thickness of the GaAlAs layer causes an increase in the light emission output, but one reason is that the current density flowing through the Pn junction becomes uniform and the light emission extraction area increases. That is for sure.

In order to further increase the thickness of the n-GaAlAs layer, the temperature at the point B, which is the growth start point, may be increased.
The maximum temperature is 860 to keep the thickness of the GaAlAs layer as before.
C. or higher, and the melt composition also needs to be changed.

Although the present invention has been described with respect to a red light emitting diode,
By changing the composition of the 2p-type growth solution, it can be applied to light emitting diodes of other emission wavelengths. It should be noted that the substrate which is removed or not is also included in the scope of the present invention.

〔The invention's effect〕

According to the present invention, it is possible to manufacture a light emitting diode excellent in mass productivity without particularly requiring precise control of growth parameters and control of vapor pressure of As which makes the growth apparatus complicated and expensive.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a light-emitting diode wafer according to an example of the present invention, FIG. 2 is a diagram showing a correlation between the thickness of a third crystal layer and light-emitting output, and FIG. It is a diagram showing a schedule. 10 p-type GaAs substrate 11 p-Ga _1-x Al _x As layer (1 ≧ x> 0) 12 p-Ga _1-y Al _y As layer (1> y ≧ 0) 13 n-Ga _1-z Al _z As layer (1 ≧ z> 0)

Continuation of the front page (72) Inventor Yujiro Ueki 1-1-10 Shimotsu, Kokurakita-ku, Kitakyushu-shi, Fukuoka Prefecture Inside the Kitakyushu Plant of Toshiba Corporation (56) References JP-A-62-248270 (JP, A) JP-A-63 194374 (JP, A) JP-A-55-107281 (JP, A) JP-A-56-40679 (JP, U)

Claims (1)

(57) [Claims] 1. A p-type GaAs substrate at 860 ° C., Ga: 1 g, GaAs: 35 m
g, Al: 2.7 mg, Zn: 2.8 mg, contacted with a first p-type growth solution, cooled at a cooling rate of 0.5 ° C./min to 840 ° C., separated, and immediately Ga: 1 g, GaAs: 49 mg, Al: 1.35 mg, Zn: contacted with the second p-type growth solution consisting of 1.5 mg at the same cooling rate as above for 1 minute, separated, and immediately Ga: 1 g, GaAs: 35 mg, Al: 2.7 m
g, Te: contact with an n-type growth solution consisting of 5 μg and cooling rate of 0.
A method for producing a light-emitting diode, comprising a step of lowering the temperature to 650 ° C. at 5 ° C./min, separating and allowing to cool.