JPS5924556B2 - gallium phosphide green - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a light emitting device using a light emitting device using a biasing force, particularly Ga9ium phosphide.
The present invention relates to a green light emitting device made of P crystal.

Recently, semiconductor light emitting devices, such as light emitting devices using compound semiconductor crystals such as GaP or gallium arsenide phosphide, GaAsP, have been widely used for various displays.

Among these, for example, GaP light emitting elements emit light from green to red,
The aAsP light-emitting element emits yellow to red light. Among these types of light emitting devices, a green GaP light emitting device or a yellow GaAsP light emitting device is doped with nitrogen N atoms as a luminescent center impurity. This nitrogen-doped light emitting device, for example, a green GaP light emitting device, can be obtained as follows. That is, an n-type GaP layer is formed on an n-type GaP substrate by liquid phase epitaxial growth or vapor phase epitaxial growth, and then l! ) P-type Ga
A P layer is formed to form a P-n junction. The nitrogen atom, which is the luminescent center, is located in the n-type GaP layer and the p-type G layer.
It is added in the aP layer. By the way, this nitrogen atom is
It is preferable that it is added at a high concentration near the pn junction where it is substantially effective for light emission. That is, if a large amount of nitrogen is added near the pn junction, the luminous efficiency will be high. Therefore, the present inventors conducted various experiments in order to add a large amount of nitrogen near the pn junction. One of them is n-type G
An investigation of the relationship between the donor concentration (the donor concentration here refers to the net donor concentration, i.e., −) of the n-type GaP layer on the aP substrate and the nitrogen concentration revealed that it is inversely proportional to the growth direction. found. In other words, the donor concentration in the n-type GaP layer increases monotonically in the growth direction due to the fact that the segregation coefficient is usually smaller than 1, and the nitrogen concentration NT added in one direction increases.
As measured by absorption spectroscopy and photoelectric measurement, it was found to decrease in the growth direction. Therefore p−n
If the nitrogen concentration NT, which is the luminescent center near the junction, is low, it becomes a cause of lowering the luminous efficiency. The present invention deals with the above-mentioned experimental facts, and configures the GaP layer constituting the p-n junction on the n-type GaP substrate so that the donor concentration decreases stepwise in the growth direction, contrary to the conventional method, and emits light. The central nitrogen is p
The present invention provides a GaP green light-emitting element in which luminous efficiency is improved by including the phosphor in the n-type GaP layer on the -n junction side.

An embodiment of the present invention will be described below with reference to the drawings.

First, an n-type GaP layer was formed on an n-type GaP substrate using a liquid phase epitaxial growth apparatus as shown in FIG.
Next, a p-type GaP layer is formed on this n-type GaP layer, and p-
An n-junction is formed to obtain a GaP green light emitting device.

The luminous efficiency of the GaP green light emitting device thus obtained is as high as about 0.23%. The method of this example will be specifically explained below. First, the growth apparatus shown in FIG. 1 includes a growth boat 12 placed inside a quartz reactor 11, and two heating devices 13a and 13b placed outside the reactor 11.
The growth boat 12 is equipped with a slider 15 having a recess 14a for accommodating an n-type GaP substrate 14, and a solution 16 having a portion accommodating a solution 16 and a small hole 17 for doping with impurities. Covers 14b and 16b made of quartz, for example, are provided on the wide n-type GaP substrate 14 and the solution 16.
An impurity evaporation source 19 made of zinc Zn, for example, is provided at a portion a little apart from this growth boat 12.
Further, on both sides of the reactor 11, there are openings 11a and 11a' for supplying gas, and an opening 11b for discharging gas.
is provided. With such a growth apparatus, n-type GaP
When forming an n-type GaP layer and a p-type GaP layer on a substrate, the growth boat 12 is driven as shown in FIGS. 2A, b, and c. First, as shown in FIG. 2a, the recess 24a of the slider 25 made of graphite is filled with sulfur S doped n-type G.
The aP substrate 24 is installed, 5g of Ga is stored in the solution storage tank of the solution storage boat 28, and the heating device is operated to raise the temperature of the growth boat 12 to 1010° C. while flowing H2 gas from the gas supply port 11a' to make the growth boat 12 unsaturated. A Ga solution 26 containing no donor impurities (containing naturally occurring donor impurities such as silicon) is prepared. Like this 101
15 minutes after the temperature reaches 0°C, the slider 25 is moved to bring the GaP substrate 24 into contact with the solution 26 as shown in FIG. 2b, and the solution 26 is placed on the GaP substrate 24 as shown in FIG.
6 is moved to the part having a large number of small holes 27 with a part of it placed thereon. At this time, the thickness of the solution 26 on the GaP substrate 24 is, for example, 1.5? The depth of the recess 24a of the slider 25 is set so that the depth of the recess 24a of the slider 25 is set so that In this state, for example 1
The surface of the GaP substrate 24 is dissolved into the solution 26 for 0 minutes, and then cooled to a predetermined temperature, eg, 960° C., at a constant cooling rate, eg, 1.5° C./min.

When the temperature reaches 960° C., the temperature is kept constant for a predetermined period of time, for example, 60 minutes, and at the same time, H and gas containing ammonia NH are introduced from the gas supply port 11a. In this way, the inflowed ammonia reacts with the gallium solution 26 on the GaP crystal through the large number of small holes 27 in the state shown in FIG. 2c, and a high concentration of N is added to the gallium solution. After 60 minutes have elapsed, the solution is cooled again to 900° C. at a cooling rate of 1.5° C./min, for example, to grow an n-type GaP layer to which nitrogen atoms are added at a high concentration.

Subsequently, when the temperature reaches 900°C, the temperature is kept constant for a predetermined time, for example, 30 minutes, and at the same time as the holding starts, the heating device 13b of the impurity evaporation source 19 made of, for example, Zn shown in FIG. 1 is operated to raise the temperature to, for example, 560°C. Keep it warm at that temperature. In this way, Zn is evaporated and is sent together with, for example, H and gas from the gas supply port 11a'' shown in FIG. .Then add the solution again to e.g. 1.5
Cooled down to 800℃ at a cooling rate of ℃/min,
A p-type GaP layer is grown on the P layer, and then the heating device 13a
And the power source (not shown) of 13b is used to cool the cutting blade naturally. By the way, the temperature programs of the growth boat 12 and the impurity evaporation source 19 described above are distributions as shown in FIGS. 3A and 3B, as is clear from the above-mentioned points. The n-type Ga on the n-type GaP substrate thus obtained
As shown by the solid line in FIG. 4, the donor concentration distribution of the P layer began to decrease significantly stepwise in the growth direction. This is because when growing an n-type GaP layer by liquid phase epitaxial growth, GaP is unsaturated and does not contain donor impurities.
Once the GaP substrate surface is dissolved in a solution, this dissolved G
This seems to be due to the fact that the aP solution is reprecipitated in a hydrogen atmosphere in the first half and in a hydrogen atmosphere containing ammonia in the second half. That is, in the first half of epitaxial growth, the surface of the quartz reaction tube is reduced by hydrogen gas, so it is thought that high concentration silicon Si is mixed into the gallium solution, and as a result of this, the n-type GaP layer grown in the first half A high concentration of Si is added.

On the other hand, since the second half of the growth is carried out in a hydrogen atmosphere containing ammonia, a large amount of nitrogen is added to the gallium solution, and some of the nitrogen forms stable compounds with Si dissolved in the solution. The Si concentration decreases, and the donor impurity in the solution is mainly sulfur brought about by the dissolution of the substrate crystal.
It is considered that the donor concentration of the P layer becomes lower. Therefore, it seems that the impurity distribution of the n-type GaP layer changes stepwise because the epitaxial growth is performed in a hydrogen atmosphere containing ammonia. For comparison, when ammonia is added at the time of initial temperature rise or at the start of growth of the n-type GaP layer, the donor concentration of the n-type GGaP layer becomes low as shown by the dotted line in Figure 4. The luminescent center impurity concentration NT of the entire n-type GaP layer is high, for example, on the order of 2×10 18 /~, which absorbs light and causes a decrease in external luminous efficiency. Become. Also, as shown above, the first half of the n-type GaP layer (part with high donor concentration)
Since the donor impurity is Si, the crystallinity is better than when forming an n-type GaP layer with a donor impurity such as sulfur.

Therefore, since the donor concentration near the p-n junction of the n-type GaP layer composed of donor impurities such as sulfur becomes low, the external luminescence efficiency decreases due to the green emission center impurity near the p-n junction. A certain N concentration NT is as high as 2×10 18 /d. Therefore, the luminous efficiency is
This is greatly improved due to the increase in hole injection from the layer to the n-type GaP layer and the increase in the emission center impurity concentration. In the above embodiment, ammonia is added at around 20 Pm during the growth of the n-type GaP layer, but it may be around 15 μm to 25 μm.

This was epitaxially grown to 60 μm and p-type GaP
In the case where the layer is 20 μm and the thickness of the grown or p-type GaP layer is different, the value is not limited to the above value. However, the conditions for this are to eliminate changes in nitrogen concentration near the n-type GaP layer (2 to 5 μm) near the p-n junction, which is the light emitting region, to improve crystallinity, and to improve the crystallinity due to the absorption of light by nitrogen, as described above. The goal is to reduce Further, in the above embodiments, the n-type GaP layer was grown by liquid phase epitaxial growth in a hydrogen atmosphere, but it may be grown in an argon atmosphere, for example.

For example, if ammonia is added in an Ar atmosphere, part of the nitrogen (ammonia) forms a stable compound with Si dissolved in the solution, reducing the Si concentration in the solution, as described above. The donor impurity is mainly sulfur brought about by dissolving the substrate crystalb1. Therefore, if the donor concentration of the n-type GaP layer that grows after adding ammonia is low, it will be reversed to p-type. There are cases. Furthermore, in the above embodiments, sulfur S was used as a donor impurity for the n-type GaP substrate, but tellurium Te or selenium S
The acceptor impurity of the p-type GaP layer is not limited to Zn, but may be Cd.

Furthermore, the numerical values explained in the above embodiments are not limited thereto and can be changed in various ways.

[Brief explanation of drawings]

FIG. 1 is a sectional view schematically showing a liquid phase epitaxial growth apparatus used in the method of one embodiment of the present invention, and FIGS. 2 a to 2 c are sectional views showing how the growth boat of the apparatus shown in FIG. 1 is driven. , 3rd
Figure 1 is a curve diagram showing the temperature profile of the growth boat of the apparatus and the impurity evaporation source, and Figure 4 is a diagram showing the impurity profile of a light emitting device obtained by the method of one embodiment of the present invention. It is. 11... Reactor, 12... Growth boat, 13a,
13b... Heating device, 14, 24... N-type GaP substrate, 14a, 24a... Recessed portion for accommodating the substrate, 14b
, 24b, 16b, 26b... one lid, 15, 25-...
Slider, 16, 26...Solution, 17, 27...
Small hole, 18, 28...solution storage boat, 19...impurity evaporation source, 11a, 11aξ...opening for supplying gas, 11b...opening for discharging gas.

Claims (1)

[Claims] 1. In a gallium phosphide green light-emitting device in which a gallium phosphide layer constituting a pn junction is provided on an n-type gallium phosphide substrate, the donor concentration of the gallium phosphide layer changes from the substrate side toward the surface. 1. A gallium phosphide green light-emitting device, characterized in that the gallium phosphide layer on the surface side is configured to decrease in steps, and the gallium phosphide layer on the surface side contains nitrogen.