JPH0330311B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a light emitting semiconductor device,
In particular, the present invention relates to a high-brightness light emitting semiconductor device having four epitaxial layers.

Conventional configurations and their problems Gallium phosphide (GaP), gallium arsenide (GaAs)
A light-emitting device using a − group compound semiconductor such as
Currently used in a wide range of fields. With the expansion of such application fields, there is a strong demand for even higher efficiency, and the efficiency of various commercially available light emitting elements has generally been improved by several tens of percent in recent years. However, GaP pure green light emitting diodes (hereinafter referred to as LEDs), which have an emission wavelength of 555 nm, still have a low efficiency of 0.07%. This is because light emission is caused by free excitons in the crystal, and is therefore greatly affected by the quality of the crystallinity, such as the etcipit density.

Figure 1 shows a commonly used GaP pure green LED.
This is a cross section of It has a three-layer structure in which an n-type GaP epitaxial layer 2 is formed on an n-type GaP substrate 1 and a p-type GaP epitaxial layer 3 is formed thereon, and n- and p-side electrodes 4 and 5 are provided.

FIG. 2 shows an example of the relationship between luminous efficiency and etching pit density of an LED having the structure shown in FIG. The etch pit density in the p-type GaP epitaxial layer 3 is taken as the etching pit density. As is clear from the figure, the luminous efficiency increases as the etching pit density decreases. In order to achieve high efficiency,
It is essential to reduce the etched pit density (hereinafter abbreviated as EPD) at the p-n junction interface, and to this end, it is necessary to use a low-EPD substrate wafer, and to increase the thickness of the epitaxial layer by increasing the thickness of the epitaxial layer.
Mitigating the effects of EPD is effective.

FIG. 3 shows this effect and is a diagram showing the relationship between the EPD and the thickness of the epitaxial layer 2. As is clear from the figure, as the thickness increases
EPD is decreasing.

On the other hand, the emission wavelength of GaP pure green LED is 555nm.
Since it is close to the absorption edge of GaP, the reabsorption of emitted light is large. Therefore, the closer the light-emitting region is to the external surface, the more advantageous it is, and in the structure shown in FIG. 1, it is more advantageous for the p-type region 3 to mainly emit light.
Therefore, n ⁺ p ^- improves the injection efficiency into the p region.
The structure becomes suitable and the n epitaxial layer 2
It becomes necessary to make the carrier concentration higher than that of the p epitaxial layer 3, for example, about 1×10 ¹⁸ cm ⁻³ .

As described above, in order to achieve high efficiency in a GaP pure green LED, it is necessary to increase the thickness of the n epitaxial layer 2 and increase the carrier concentration. However, increasing the thickness of the n-epitaxial layer 2 increases the absorption of the emitted light in the region and reduces the back surface reflection effect, so that the luminous efficiency tends to decrease. As described above, there has been a problem in that increasing the thickness of the n epitaxial layer to reduce the EPD and increasing the carrier concentration to improve the injection efficiency are in a contradictory relationship.

Purpose of the invention The present invention aims to solve the above problems,
The present invention provides a light emitting semiconductor device that simultaneously reduces EPD and reabsorption effect and achieves high efficiency.

Structure of the Invention FIG. 4 is a diagram showing a cross section of an LED that is an embodiment of the present invention. The structure of the present invention includes an n-type GaP substrate 6 with a carrier concentration of 3 to 5 x 10 ¹⁷ cm ^-3 as a first layer, and a second layer on top of the n-type GaP substrate 6 with a carrier concentration of 2 to 5 × 10 17 cm -3.
A low concentration n-type GaP epitaxial layer (n ₁ ) 7 with ×10 ¹⁷ cm ^-3 is formed to a thickness of 60 μm or more, and then a high concentration with a carrier concentration of 0.8 to 1.5 × 10 ¹⁸ cm ^-3 is formed as the third layer. N-type GaP epitaxial layer (n ₂ ) 8 with a thickness of 10 μm
to form. Furthermore, on top of that, a low concentration p-type GaP layer with a carrier concentration of 0.5 to 1.5×10 ¹⁷ cm ^-3 is formed as a fourth layer.
The epitaxial layer (p ₁ ) 9 is grown to 10 μm, and then a high concentration of 0.9 to 2.0×10 ¹⁸ cm ^-3 is grown as the fifth layer.
p ⁺ type GaP epitaxial layer (p ₂ ) 10 with a thickness of 10μ
It has a five-layer structure grown to about m. According to this, carrier injection is performed from the third layer near the surface to the fourth layer, and high injection efficiency and low reabsorption effect can be achieved.

DESCRIPTION OF EMBODIMENTS In the present invention, the n ₁ layer 7 is formed on the n ⁺ substrate 6 in order to reduce EPD. High efficiency
To realize an LED, the EPD is preferably about 1.5×10 ⁴ or less, and as shown in Figure 3, it is about 60μ
m, but in order to reduce the aforementioned absorption effect as much as possible, the carrier concentration was set to 5×10 ¹⁷ cm.
^-3 or below. FIG. 5 shows the carrier concentration dependence of this absorption effect. Reducing the carrier concentration is effective in reducing the absorption effect, but when it becomes less than 10 ¹⁷ cm ^-3 , the resistance component increases and the forward voltage increases. From this point of view, the optimum concentration of the n ₁ layer 7 is 2 to 5×10 ¹⁷ cm ⁻³ .
Since sufficient injection efficiency into the p-region cannot be obtained in this concentration range, next, a high concentration of 0.8×10 ¹⁸ cm ^-3 or higher is recommended.
An _n2 layer 8 is formed on the _n1 layer 7. However, n ₂
As the thickness of layer 8 increases, absorption occurs and the luminous efficiency decreases, as shown in FIG. At a concentration of 1×10 ¹⁸ cm ⁻³ , the effective thickness is limited to approximately 10 μm.

On the other hand, FIG. 7 shows the relationship between the concentration of the _p1 layer 9 and luminous efficiency. As is clear from the figure, when the conditions of the n ₁ and n ₂ layers are kept constant, as the p carrier concentration decreases, the injection of electrons into the p region increases and the luminous efficiency increases. When the carrier concentration becomes 5×10 ¹⁶ cm ^-3 or less, the forward voltage increases due to the aforementioned increase in series resistance, so there is a limit to lowering the carrier concentration, and the carrier concentration becomes 0.5 to 1.5×10 ¹⁷ cm ^-3 is acceptable. Further, the thickness of the _p1 layer 9 is desirably 10 μm or less in order to prevent an increase in series resistance. In this range of carrier concentration, good ohmic contact cannot be obtained even if a p-side electrode is formed. Additionally, a uniform current does not flow across the entire pn junction surface, causing a decrease in brightness and unevenness. The p ₂ layer 10 is provided to improve this drawback, and has a p carrier concentration of 1×10 ¹⁸ cm ^{−3 or} more. Of course, if this p ₂ layer 10 becomes thicker, light will be reabsorbed and the luminous efficiency will decrease, so the limit is about 10 μm.

The structure described above is manufactured under the following conditions.
First, the first layer is 4×10 ¹⁷ cm doped with sulfur (S).
^-3 n-type GaP substrate 6 is used, and the first n-type melt is brought into contact with the substrate at 1020° C. by employing a normal liquid phase epitaxial method. This melt contains sulfur (S), which is a donor impurity, at a concentration of 5×10 ^-5 mol% relative to gallium (Ga).
It's doped. and at a rate of 1°C/min.
By slowly cooling from 1020℃ to 800℃, 4×
10 ¹⁷ cm ⁻³ , 60 μm n ₁ layer 7 is grown.

Next, a slide boat is prepared, and three types of melts, second, third, and fourth, are installed. The second melt contained 2.5×10 ^-4 mol% of S, the third melt contained 5×10 ^-3 mol% of zinc (Zn) as an acceptor impurity,
Then, the fourth melt is doped with Zn in an amount of 7×10 ⁻² mol % relative to Ga. And above n ₁
After the layer 7 has been grown, the substrate 6 is brought into contact with the second melt at 920°C and slowly cooled to 900°C to form the _n2 layer 8. The concentration is 0.85×10 ¹⁸ cm ^-3 and the thickness is
It is 9.0 μm. Next, the second melt was extracted at 900°C, and the third melt was brought into contact with it and slowly cooled to 850°C, thereby forming a _p1 layer 9 of 1.0×10 ¹⁷ cm ^-3 and 8 μm thick.
grow. Furthermore, by slowly cooling to 780° C., a P ₂ layer 10 of 1.0×10 ¹⁸ cm ⁻³ and 8 μm is formed.

The GaP pure green light emitting diode obtained as described above has a luminous efficiency of 0.14%, which is about twice as high as that of conventional ones.

Effects of the Invention As described above, the present invention has a five-layer structure, and by improving crystallinity and reducing the light reabsorption effect, it is possible to provide a highly efficient GaP pure green light emitting semiconductor device. I can do it.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a conventional GaP light emitting diode.
FIG. 2 is a diagram of the relationship between luminous efficiency and etchip density, FIG. 3 is a diagram of the relationship between etchip density and the thickness of the n-epitaxial layer _n1 , and FIG.
A cross-sectional view of a light emitting diode. Figure 5 shows the relationship between luminous efficiency and the carrier concentration of the n ₁ layer when the thickness of the n ₁ layer is constant. Figure 6 shows the relationship between the carrier concentration of the n ₂ layer and the n 2 layer. FIG. 7 is a diagram showing the relationship between the luminous efficiency and the thickness of the _n2 layer, and FIG. 7 is a diagram showing the relationship between the luminous efficiency and the carrier concentration of the _p1 layer. DESCRIPTION OF SYMBOLS 1... Substrate, 2, 3... N- and p-type epitaxial layers, 4, 5... n- and p-side electrodes, 6...
...substrate, 7,8...n-type epitaxial layer n ₁ ,
n ₂ , 9, 10...p-type epitaxial layers p ₁ , p ₂ .

Claims (1)

[Claims] 1 A first layer made of an n-type gallium phosphide substrate and having a carrier concentration of 3 to 5 x 10 ¹⁷ cm ^-3 and a first layer formed on this first layer and having a carrier concentration of 2 to 5.
×10 ¹⁷ cm ^-3 , a second layer consisting of a low concentration n-type gallium phosphide epitaxial layer selected to have a thickness of 60 μm or more, and a carrier concentration of 0.8 to 1.5 formed on this second layer. ×10 ¹⁸ cm ^-3 and a third layer consisting of a high concentration n-type gallium phosphide epitaxial layer selected to have a thickness of 10 μm or less, and a carrier concentration of 0.5 to 1.5 formed on this third layer. ×10 ¹⁷ cm ^-3 , the thickness is
a fourth layer consisting of a low concentration p-type gallium phosphide epitaxial layer selected to have a thickness of 10 μm or less;
formed on a layer with a carrier density of 0.9 to 2.0×
10 ¹⁸ cm ^-3 and a fifth layer consisting of a highly concentrated p-type gallium phosphide epitaxial layer selected to have a thickness of 10 μm or less.