JPS606552B2 - Gallium phosphide green light emitting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor light emitting device, and particularly relates to a semiconductor light emitting device using gallium phosphide (
The present invention relates to a green light emitting device using GaP) crystal.

A conventional GaP green light-emitting device generally has a structure in which an n-type Gap layer and a p-type GaP layer are provided on an n-type Gap substrate, and the impurity concentration distribution is usually as shown by the dotted line in Figure 1a. .

For example, Appl. ph. Le
tt. Vol. 22, pages 227 to 229 (literature)
According to the description, the minority carrier lifetime and luminous efficiency of the n-type Gap layer and the p-type Gap layer are determined when the impurity concentrations of the respective layers are approximately 1×1 and 7/2 and approximately 1×1 and 8/2, respectively. It is at its maximum during the earth. Based on these facts and considering the injection efficiency of minority carriers in the vicinity of the pn junction, it is possible to consider a device configuration that provides relatively high luminous efficiency. In fact, when the impurity concentrations of the n-type GaP layer and the p-type GaP layer are set to the above-mentioned concentrations, a luminous efficiency of about 0.1% (with mold) will be exhibited. Incidentally, the technology for growing high-pressure pulled Gap crystals (LEC crystals), which serve as substrates for manufacturing light-emitting devices, has advanced significantly in recent years, and high-quality GaP crystals with low crystal defects, residual strain, etc. can now be obtained.

When such a high-quality GaP crystal is used as a substrate, the GaP formed on it (liquid phase epitaxial growth)
It is thought that the crystallization of the layers (n-type and p-type) also improves,
It is necessary to reconsider the above-mentioned element configuration (including impurity concentration). Therefore, the present inventor has developed the above-mentioned high-quality Ga.
A detailed study of the relationship between minority carrier lifetime and donor concentration in an n-type GaP layer formed by liquid-phase epitaxial growth on a P substrate revealed that the minority carrier lifetime was improved, especially at lower donor concentrations than in the past. As shown in Figure 1b
It has been found that this is particularly noticeable when the donor concentration is reduced stepwise in the growth direction as shown by the solid line.

Figure 2a shows the lifetime of minority carriers with respect to the donor concentration in the n-type Gap layer.For comparison, b shows the case where the donor concentration distribution is not step-like, and c shows the case in the above literature.
Shown below. When a light emitting device was created based on this result, a light emitting device with an average luminous efficiency of 0.4% or more (with mold, 2nd/second case) could be obtained. Therefore, the inventors of the present invention first disclosed this fact in a patent application (Japanese Patent Application No. 1200-1980)
No. 3) I did it. However, the above-mentioned high luminous efficiency gap
In the configuration of the green light-emitting element, no improvements were made to the p-type Gap layer.

Therefore, the present inventors investigated n-type Ga, which has a long minority carrier life.
With respect to the p-type Gap layer grown on the p-layer, the influence of acceptor concentration on the lifetime of minority carriers in the n-type Gap layer and the p-type Gap layer was studied.

As a result, for the p-type GaP layer, an improvement was seen when the acceptor concentration was low, for example, 2 × 1 and 7 / 40 seconds.
I saw that I could get more than EC and issued it. Furthermore, the acceptor concentration affects not only the p-type Gap layer but also the n-type Gap layer.
It was also found that when the concentration is low as in No. 3y, the lifetime of minority carriers in the n-type gap layer near the p-n junction is improved. The present invention was made in view of the above experimental facts, and has an average luminous efficiency of approximately 0.5% (with mold, 25A
1) A Gap green light emitting device which can be obtained as described above is provided.

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

First, using a liquid phase epitaxial growth apparatus as shown in FIG. 3, a donor concentration (N) is grown on an n-type GaP substrate.

) is formed in a stepwise manner, and a p-type Gap layer in which the acceptor concentration (N^) similarly changes in a stepwise manner is formed thereon to obtain a Gap green light emitting device. If No of the n-type GaP layer and N^ of the p-type GaP layer are configured to change stepwise in this way, extremely high luminous efficiency can be obtained. This is the emission center concentration (N
T) is as high as approximately 2×18/ground and is n-type Ga.
This is because the lifetime of minority carriers in the p-layer and p-type GaP layer has become extremely long. This will be explained in detail below. First, in the growth apparatus shown in FIG. 3, a growth boat 12 is arranged inside a reactor 11 made of quartz, and two
The growth boat 12 has a recess 14 that accommodates the n-type Gap substrate 14.
The slider 15 is composed of a slider 15 having a diameter of 15 mm and a solution accommodating port 18 having a portion for accommodating the solution 16 and a small hole 17 for doping with impurities. For example, a lid 14b made of quartz,
16b is provided. And this growth boat 12
An impurity evaporation source 19 made of, for example, zinc (Zn) is provided at a portion a little apart from the above.

Further, on both sides of the reactor 11, there are provided closures 11a and 11 for supplying gas, and a closure 11b for discharging gas. When forming an n-type GaP layer and a p-type Gap layer on an n-type Gap substrate using such a growth apparatus,
This is done by driving the growth boat 12 as shown in FIGS. 4a, b, and c. First, as shown in FIG. 4a, a high-quality sulfur (S)-doped material (Dislocation pit: 1 x 1 /
n-type Gap (on average, about 5 to 8
The substrate 24 is installed, 5 tons of Ga is stored in the solution storage tank of the solution storage boat 28, and the heating device is operated while gas is supplied from the gas supply row 1 to the growth boat 12.
010qo and does not contain donor impurities (
A Ga solution 26 (containing naturally occurring donor impurities such as silicon) is prepared. 15 minutes after reaching 101000 in this way, the slider 25 is moved and the fourth
As shown in FIG. b, a portion of the solution 26 is placed on the Gap substrate 24 and moved to a portion having a large number of small holes 27. At this time, the recess 24a of the slider 25 is adjusted so that the thickness of the solution 26 on the Gap substrate 24 is, for example, 1.3 ribs.
Set the depth. This state is maintained for 10 minutes, for example, so that the surface of the Gap substrate 24 dissolves into the solution 26, and then the cooling rate is maintained at a constant rate, for example 1. It is cooled down to a predetermined temperature, for example, 980 yo/min. Due to this cooling, the GaP substrate 2
4. Nitrogen-free n-type GaP shown in FIG. 6, which will be explained later on.
A layer (referred to as the ln-th layer) grows to about 15 layers. N of the ln-th layer that has grown to this state. is the N of the n-type Gap substrate.
A little less than o. For example, as shown in FIG.
is 1.8 x 1 to 7/digits.

N of this lnth layer. As will be explained later, since the surface of the quartz reaction tube constituting the growth furnace is reduced by hydrogen gas, a large amount of Sj is mixed into the solution, and the concentration may be higher than that of the substrate, for example. Subsequently, after reaching 980 oo, the temperature is kept constant for a predetermined period of time, for example, 60 minutes, and at the same time as the holding starts, argon (~) gas containing ammonia (NH3) is flowed in from the gas supply port 11a. In this way, as will be explained later, the injected ammonia reacts with the gallium solution 26 on the Gap substrate through a large number of small holes in the state shown in FIG. At the same time, a portion of the gallium solution 26 reacts with silicon (Si), which comes from quartz in the furnace, to form Si3N4. Also solution 2
S in 6 is partially evaporated during this holding time. Then, after 60 minutes have elapsed, the solution is cooled again to 94,000 at a cooling rate of, for example, 1.5 oo/min.

By this cooling, n-type Ga is formed on the partially grown ln layer.
A p-layer (referred to as the first layer) is grown. This state is the 6th
In the figure, 30 layers are grown in the entire n layer.
The grown second layer contains a very large amount of nitrogen and has very little ND, for example, as shown in FIG. Continued 940
After the temperature reaches 0, the temperature is kept constant for a predetermined period of time, for example, 30 minutes, and at the same time, the heating device 13b of the impurity evaporation source 19 made of, for example, Zn shown in FIG. 3 is operated to raise the temperature to, for example, 460 qo. Keep warm at that temperature. When kept warm in this way, Zn with a high vapor pressure evaporates and flows into the n-type Gap layer (both the first and second ) enters the solution 26 on the substrate on which it is grown. After this, the solution is again cooled to 0° C. at a cooling rate of 1.5 qo/min. In this way, Zn is grown on the substrate on which the n-type GaP layer is grown.
A p-type Gap layer (referred to as lp layer) doped with x1 and 6/sphere is grown. Subsequently, the temperature is kept constant at 0° C., for example, for three batches, and at the same time the temperature of the impurity evaporation source 19 is raised to 560 do, and the gas supply is stopped.
After this, the solution was cooled again to 800 qo at a cooling rate of 1.5°C/min.
Cool until In this way, a p-type GaP layer (referred to as the "first layer") with a low nitrogen concentration and doped with 2×l and 8/Zn is grown to a thickness of about 15 rm. After this, the heating devices 13a and 13b are turned off (not shown) and allowed to cool naturally.

By the way, the above growth boat 12 and impurity evaporation source 19
As is clear from the above-mentioned points, the temperature program has a distribution as shown in FIGS. 5a and 5b. The distribution of the donor concentration of the n-type Gap layer and the acceptor concentration of the p-type GaP layer on the n-type Gap substrate thus obtained changes stepwise in the growth direction, as shown by the solid line in FIG. It was way.

This was explained briefly in the above example, but when growing the ln-th layer, the GaP substrate surface is once dissolved in a solution that is unsaturated with Gap and does not contain donor impurities, so the No.
As is clear from FIG. 6, the order is 1.8×1 and 7/position 1 and 7/lump order. Note that during the growth of this ln-th layer, the surface of the quartz reaction tube constituting the growth furnace is reduced by hydrogen gas, so a large amount of Si is mixed into the solution. The main donor impurity of the layer is Sj (No is the above value). On the other hand, the second layer grown in the second half is grown in a gas atmosphere containing ammonia, so a large amount of nitrogen is added to the gallium solution, and some of the nitrogen and Si in the solution form a stable compound. Si, the main donor impurity in the solution, is reduced. Therefore, the donor concentration of the first layer is mainly determined by the donor impurity (S in this example) dissolved from the substrate, and the first layer No. is compared to the ln layer as shown in FIG. It's about one digit lower. In this way, N of the lnth layer. and N of the first layer. As will be explained later, when the crystal defects from the substrate are removed by the step-like donor distribution structure of the ln-th layer and the ln-th layer and the second layer, as will be explained later, The crystallinity of the layer is improved, that is, even when nitrogen is added at a high concentration, the lifetime of minority carriers in the layer can be lengthened, thereby improving the luminous efficiency. Furthermore, when a p-type GaP layer is epitaxially grown on an n-type Gap layer with good crystallinity, the minority carrier ratio with respect to the acceptor concentration of the p-type GaP layer (lp layer) is as shown in Figure 7a. The dependence of lifetime also increases on the low concentration side compared to the conventional example shown in c.

For comparison, when a p-type Gap layer is grown on an n-type GaP layer that does not have a step change in the donor concentration in b (the donor concentration of the n-type GaP layer is 3 × 1 and 6/mass). (fixed nearby). As is clear from FIG. 7, as the crystallinity of the n-type Gap layer improves, the lifetime of minority carriers in the p-type Gap layer (lp layer) grown thereon also improves, especially at low acceptor concentration. So, n-type Ga
The dependence on the p-layer characteristics is significant. Furthermore, when the acceptor concentration of the p-type Gap layer is made low, the crystallinity of the n-type GaP layer is also affected, and as shown in Figure 8, the lifetime of minority carriers in the n-type Gap layer is slightly improved. In Figure 8, a represents the acceptor concentration of the p-type Gap layer (lp layer) by 7.
When the value is approximately ×10 16 /mass, b is approximately 2 × 10 18 /mass, and b represents the relationship between the donor concentration of the n-type GaP layer (second layer) and the lifetime of minority carriers.
As shown in FIG. 8, the dependence of the characteristics of the n-type gap layer (first layer) on the acceptor concentration of the p-type gap layer (first layer) is as follows:
This is thought to be due to distortion caused by a rapid change in impurity concentration at the pn junction.

In this way, it was found that as the characteristics of the substrate and the n-type Gap layer grown on it improve, the characteristics of the p-type Gap layer (lp layer) also improve, and this is particularly noticeable in the low acceptor concentration region compared to the conventional one. .

Based on this result, a light emitting device was fabricated and its luminous efficiency was examined. As a result, the donor concentration of the n-type Gap layer was changed stepwise, and the donor concentration of the ln-th layer was set to 1 to 5 × 1 and 7 / ground,
The donor concentration of the first layer is 1 to 5×1 to 6, and p
The type GaP layer was also changed stepwise in the same way, and the acceptor concentration of the first lp layer was set to 2 to 10 × 1 and 6 squares, and the acceptor concentration of the first sand layer was set to 1.5 to 20 × 1 and 7 squares. It has been found that stable luminous efficiency can be obtained at certain times.

The average luminous efficiency at this time was 0.5% (with mold, 2
pine tree) or more. Furthermore, based on the above impurity concentration, we investigated the luminous efficiency with respect to the growth thickness of the ln-th layer, the second layer, and the lp-th layer. It was also found that the average luminous efficiency was more than 0.5% (with mold, 2cm) at ~30mm.

As is clear from the above explanation, the lth
The number of the n layer is 1~5 x 1 and 7/ground, the number of the first layer is 1~
5 × 1 and 6 / ground, and N of the lp layer of the p cram school Cap layer
＾ is 2 to 10 x 1 bi6/uniform, N^ of the first sand layer is 1.5 to 2
If the structure is such that nitrogen is contained in the first layer and the lp layer, green luminous efficiency of 0.5% or more will be exhibited on average.

Note that the measurement of NT shown above is performed using lEEETransa.
CTons on Electron Devices
．． Vol. ED-2 state o. 7, pages 951 to 955.

To measure the lifetime of minority carriers, first calculate the lifetime of minority carriers in an element in which only the p-type Gap layer or n-type Gap layer mainly contributes to light emission by the method shown in the above literature, and then for any element. The diffusion length (L) was determined using SEM, and the lifetime (months) of minority carriers in the n-type GaP layer and the p-type Gap layer was determined from the ratio thereof.
Here, assuming that the carrier diffusion constant is constant, it is determined from the relationship L20↑. Further, No shown above is the net donor concentration 0, No-N^, and NA is the net acceptor concentration 0, N^1 No.

Furthermore, in the above embodiments, sulfur (S) was used as the donor impurity of the n-type GaP substrate, but tellurium (Te) or selenium (Se) may also be used, and the acceptor impurity of the p-type GaP layer is limited to Zn. It may be Cd instead.

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

[Brief explanation of the drawing]

Figure 1 is a curve diagram showing the impurity concentration distribution of a GaP green light emitting device, where a shows the impurity concentration distribution of a general Gap green light emitting device, and b shows the GaP
This shows the impurity concentration distribution of a p-green light emitting element.
The figure is a curve diagram showing the lifetime of minority carriers for No in the n-type GaP layer, where a shows the case where the donor concentration of the n-type GaP layer changes stepwise as shown in Tokuiso Sho 52-12003y, and b 3 shows the case where the donor concentration of the n-type GaP layer does not change stepwise, and c shows the case of a general Gap green light emitting device. Figure 3 shows the liquid phase used in the method of one embodiment of the present invention. FIGS. 4a to 4c are sectional views showing how the growth boat of the apparatus shown in FIG. 1 is driven, and FIGS. Curve diagram showing the temperature profile of the impurity evaporation source and impurity evaporation source, 6th
The figure shows the impurity profile of a light emitting device obtained by the method of one embodiment of the present invention, and FIG. In one embodiment, b is n-type Gap
c shows the case of a general GaP green light-emitting device when the layers do not change in a stepwise manner; FIG. 8 is a curve diagram showing the relationship of the minority carrier lifetime with respect to the second layer; When N^ of the lp layer is 7 x 1 and 6/block, b shows the case where the lp layer is 2 x 1 and 8/block, and Figure 9 shows the relationship between luminous efficiency and growth thickness. In the curve diagram, a shows the case of the lnth layer, b shows the case of the first layer, and c shows the case of the lpth layer. In FIG. 3 and FIG. 4, 11... Reactor, 12
...Growth boat, 13a, 13b... Heating device, 14, 24... N-type GaP substrate, 14a,
24a... Concavity for accommodating the substrate, 14b, 24
b, 16b, 26b...Lid, 15,25...Slider, 16,26...Solution, 17,27...Small hole, 18,2
8... Solution storage boat, 19... Impurity evaporation source, 11a, 11'a... Sekiguchi for supplying gas, 11a... Opening □ for discharging gas. . Figure 1 Figure 2 Figure 3 Figure 5 Figure 4 Figure 6 Figure 7 Crab Figure 9

Claims (1)

[Claims] 1. In a gallium phosphide green light-emitting device in which an n-type gallium phosphide layer and a p-type gallium phosphide layer are provided on an n-type gallium phosphide substrate, the n-type gallium phosphide layer on the substrate side Let the net donor concentration be 1×10^1^7/cm^3
~5×10^1^7/cm^3, and the net donor concentration of the n-type gallium phosphide layer on the p-type gallium phosphide layer side is 1×10^1^6/cm^3 to 5×10 ^1^6/c
The net acceptor concentration of the p-type gallium phosphide layer on the side of the n-type gallium phosphide layer is 2×10^1^6/cm^3 to 1. ×
10^1^7/cm^3, and the net acceptor concentration of the p-type gallium phosphide layer on the surface side is 1.5 × 10^1^7/
A gallium phosphide green light-emitting device characterized in that it is configured to change stepwise from cm^3 to 2 x 10^1^8/cm^3. 2. The thickness of the n-type gallium phosphide layer with high donor concentration on the substrate side is 10 μm or more, and the thickness of the n-type gallium phosphide layer with low donor concentration on the p-type gallium phosphide layer side is 10 μm.
~30 μm, and the thickness of the p-type gallium phosphide layer, which has a low acceptor concentration on the n-type gallium phosphide layer side, is 10 μm.
m ~ 30 μm, the height of the p-type gallium phosphide layer on the surface side, the thickness of the p-type gallium phosphide layer that has the acceptor concentration is 10
The gallium phosphide green light-emitting device according to claim 1, wherein the gallium phosphide green light-emitting device has a diameter of μm or more. 3. Construct so that only the n-type gallium phosphide layer with a low donor concentration on the p-type gallium phosphide layer side and the p-type gallium phosphide layer with a low acceptor concentration on the n-type gallium phosphide layer side contain nitrogen. A gallium phosphide green light-emitting device according to claim 1, characterized in that: