JPH0465036B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gallium phosphide arsenide mixed crystal epitaxial wafer suitable for manufacturing high brightness light emitting diodes.

Gallium arsenide phosphide, i.e., GaAs _1-x P _x mixed crystal epitaxial wafers are yellow, orange, etc.
Suitable for manufacturing visible light emitting diodes with wavelengths longer than 560nm.

Such mixed crystal epitaxial wafers include GaP,
It is manufactured by epitaxially growing the above-mentioned mixed crystal on a single crystal substrate of GaAs, Si, Ge, etc. However, in this case, the single crystal used for the substrate and the above
Since the lattice constant is different from that of GaAs _{1-x P} A mixed crystal ratio changing layer is provided. This is the first
This will be explained using a vertical cross-sectional model diagram of a GaAs _1-x P _x mixed crystal epitaxial wafer shown in the figure.

In this specification, the mixed crystal ratio refers to the value of x when gallium arsenide phosphide is expressed as GaAs _1-x P _x (0<x<1).

In FIG. 1, 1 is a single crystal substrate, 2 is a substrate 1
The mixed crystal percentage variable layer 3 formed above is a constant mixed crystal percentage layer. When GaP is used as the single crystal substrate 1,
The mixed crystal percentage of the mixed crystal percentage change layer 2 is gradually changed from GaP to GaAs _1-x P _x , that is, x is gradually changed from 1 to a desired value of x.

Conventionally, the rate of change of the mixed crystal ratio x in the mixed crystal ratio change layer 2 of a gallium phosphide arsenide mixed crystal epitaxial wafer with respect to the thickness, that is, △x/△l (△l;
Generally, the thickness (Δx; amount of change in mixed crystal percentage) was kept constant.

As a result of intensive research aimed at further improving the brightness of a light emitting diode using a gallium arsenide phosphide mixed crystal epitaxial wafer, the inventors of the present invention discovered that the side of the variable crystal content layer 2 in contact with the substrate 1 △x/△l of △
The authors discovered that by making x/△l smaller than the average value and forming at least one layer with a constant mixed crystal content in layer 2, it is possible to reduce various crystal defects that cause a reduction in the brightness of the light emitting diode. This invention has been achieved. The above-mentioned objects of the present invention include a single crystal substrate 1, a gallium phosphide arsenide mixed crystal ratio variable layer 2 formed on the substrate 1, and a constant gallium phosphide arsenide mixed crystal ratio formed on the layer 2. In a gallium phosphide arsenide mixed crystal epitaxial wafer consisting of layer 3, layer 2 comprises at least one layer having a constant mixed crystal percentage.
The rate of change of the above-mentioned mixed crystal percentage with respect to the thickness in the layer and in a region corresponding to 1/10 to 3/4 of the total thickness of layer 2 from the interface between substrate 1 and layer 2 is ,
This is achieved by using a wafer in which the rate of change of the mixed crystal content with respect to the thickness in the entire region of layer 2 is smaller than the average value. The average value in the entire region of the mixed crystal ratio variable layer 2 is the difference △ between the value of x near the interface between layer 2 and substrate 1 and the value of x near the interface between layer 2 and layer 3.
It is the value obtained by dividing x by the total thickness of layer 2. GaP or GaAs is preferable as the single crystal substrate 1, and Si or GaAs is preferable.
Ge can also be used. The plane orientation of the substrate 1 is preferably a {100} plane or a plane having an inclination of within 10° with respect to the {100} plane. Layer 2 is formed on substrate 1 . The thickness of layer 2 is preferably 30 to 100 μm. layer 2
The mixed crystal percentage is gradually changed from the mixed crystal percentage compatible with the substrate 1 to the mixed crystal percentage of the layer 3. In the epitaxial wafer according to the present invention, the rate of change of the mixed crystal ratio Δx/Δl with respect to the thickness is small in the early stage of growth of layer 2, that is, in the region close to the substrate 1, and large in the region close to the layer 3. do. That is, from the interface between substrate 1 and layer 2, Δx/ in an area corresponding to 1/10 to 3/4 of the total thickness of layer 2, preferably in an area corresponding to 1/3 to 1/2 Set Δl to a value smaller than the average value of Δx/Δl in layer 2, preferably 3/4 to 3/4 of the above average value.
The value should be 1/10, more preferably 3/4 to 5/10.
It is not preferable that the region in which the rate of change is reduced is less than 1/10 of the total thickness of layer 2, or even if it exceeds 3/4, since the effects of the present invention will not be exhibited.

The mixed crystal content of layer 3 formed on layer 2 is determined by the desired emission wavelength. For example, when manufacturing epitaxial wafers for orange light emitting diodes, x=0.65
form a constant layer. A pn junction is formed in layer 3. Since gallium arsenide phosphide having a mixed crystal ratio x of 0.45 or more is of indirect transition type, it is preferable to dope it with nitrogen as an isoelectronic trap if necessary. The thickness of layer 3 is 50-100μm
degree is preferred. Layer 2 and layer 3 are formed by a vapor deposition method. It is preferable that the change in the mixed crystal percentage in the layer 2 is gradual, that is, at least one layer in which the mixed crystal percentage is constant is formed in the layer 2. When carrying out stepwise, it is preferable to use the method described in JP-A-56-96384.

The brightness of the light emitting diode manufactured using the epitaxial wafer according to the present invention is different from that of the conventional light emitting diode, that is, the rate of change of the mixed crystal percentage with respect to the thickness is constant, and the mixed crystal percentage is continuously changed. The brightness is 1.8 times or more compared to light emitting diodes.

The present invention will be specifically explained based on examples.

Example: 2×10 ¹⁷ atoms/cm ³ of sulfur (S) as n-type impurity
is added, and the crystallographic plane orientation is <110 from the (100) plane.
A GaP single crystal substrate with a plane deviated by about 6° in the > direction was prepared. GaP is a single crystal substrate with an initial thickness of approximately 360 μm.
However, after degreasing using an organic solvent, mechanical polishing (mechanical-chemical polishing)
The thickness was reduced to 270 μm by chemical polishing.

Next, the polished GaP single crystal substrate and the high-purity Ga-containing quartz boat were set at predetermined locations in a horizontal quartz epitaxial reactor with an inner diameter of 70 mm and a length of 100 cm. Argon (Ar) was introduced into the epitaxial reactor to sufficiently replace and remove air, then 2500 cc/min of high-purity hydrogen gas (H ₂ ) as a carrier gas was introduced, and the Ar
The flow of water was stopped and the temperature rising process started. After confirming that the temperatures of the Ga-containing quartz boat set region and the GaP single crystal substrate set region were maintained at 760°C and 950°C, respectively, vapor phase growth of an epitaxial multilayer film GaAs _0.35 P _0.65 for an orange light emitting diode was started. did.

From the start of vapor phase growth, hydrogen sulfide (H ₂ S), an n-type impurity diluted with nitrogen gas to a concentration of 30 ppm, was introduced at 10 c.c./min, and high-purity hydrogen chloride gas (HCl) was introduced as a monogroup component. By introducing 40 c.c. per minute and reacting with Ga, it is converted to almost 100% GaCl. On the other hand, hydrogen phosphide (PH ₃ ) with a concentration of 12% diluted with H ₂ is introduced at 220 c.c. per minute. The growth temperature (corresponding to the substrate temperature) was maintained at 950°C for the first 10 minutes.
A GaP epitaxial layer was formed on a GaP single crystal substrate, and the flow rate of each gas was kept unchanged for 10 minutes.
A GaP epitaxial layer was formed by gradually decreasing the growth temperature from 950°C to 930°C. (The above is considered the first layer.) For the next 20 minutes, while keeping the growth temperature constant at 930°C, hydrogen arsenide (AsH ₃ ) diluted with H ₂ at a concentration of 12% was added at a rate of 0c.c per minute. Gradually introduced from . to 20c.c.
A second GaAs _1-x P _x epitaxial layer was formed on the first epitaxial layer with each of the above gas flows.

For the next 10 minutes, without changing the flow rate of each gas,
That is, H ₂ , H ₂ S, HCl, PH ₃ and AsH ₃ at 2500 c.c., 10 c.c., 40 c.c., 220 c.c. and 20 c./min, respectively.
.c.
During the introduction, the growth temperature was gradually lowered from 930° C. to 910° C., and a third GaAs _1-x P _x epitaxial layer was formed on the second epitaxial layer.

For the next 20 minutes, the growth temperature was kept constant at 910°C.
Furthermore, the flow rates of H ₂ , H ₂ S, HCl, and PH ₃ were kept constant at 2500 c.c., 10 c.c., 40 c.c., and 220 c.c. per minute, respectively, and only the flow rate of AsH ₃ was maintained constant. A fourth GaAs _1-x Px epitaxial layer was formed over the third epitaxial layer in increasing amounts from 20 c.c. to 60 c.c. For the next 10 minutes, the flow rates of H ₂ , H ₂ S, HCl, PH ₃ and AsH ₃ were adjusted to 2500 c.c. and 10 c.c. per minute, respectively.
While keeping 40c.c., 220c.c., and 60c.c. constant, the growth temperature was gradually lowered from 910℃ to 890℃,
A fifth GaAs _1-x P _x epitaxial layer was formed on the fourth epitaxial layer.

For the next 20 minutes, the flow rates of H ₂ , H ₂ S, HCl and PH ₃ were adjusted to 2500 c.c., 10 c.c., 40 c.c. and 220 c.c. per minute, respectively.
While keeping the cc constant and also keeping the growth temperature constant at 890℃, the flow rate of AsH ₃ was increased from 60c.c./min to 120c.c./min.
A sixth GaAs _1-x P _x epitaxial layer was formed on the fifth epitaxial layer.

For the next 40 minutes, H ₂ , H ₂ S, HCl, PH ₃ and
AsH ₃ flow rate per minute, 2500c.c., 10c.c., 40c., respectively
cc, 220c.c. and 120c.c. were kept constant, and the growth temperature was
A seventh GaAs _0.35 P _0.65 epitaxial layer was formed on the sixth epitaxial layer while keeping the temperature constant at 890°C.

For the final 40 minutes, in addition to the seventh epitaxial layer formation conditions, high-purity NH ₃ gas was added at a rate of 200 per minute.
cc is introduced and nitrogen (N) is isoelectronically
An eighth trap-doped GaAs _1-x P _x epitaxial layer was formed on the seventh epitaxial layer, completing the entire epitaxial wafer formation process.

In the above epitaxial wafer, the first to sixth epitaxial layers are layers with variable crystal content (layer 2 in Figure 1), and the total thickness is
The rate of change in the mixed crystal percentage in the region of 42.4 μm and the first 30.3 μm was 7/10 of the average rate of change.

Further, the seventh and eighth epitaxial layers are constant-mixing-crystal-concentration layers (layer 3 in Figure 1), and the thickness thereof is
The diameter was 43.4 μm, and the mixed crystal ratio x was 0.65.

Further, the n-type carrier concentration is approximately 6×10 ¹⁶ cm ^-3 in the first to seventh epitaxial layer regions, and 2.4 in the eighth epitaxial layer region doped with nitrogen.
It was ×10 ¹⁶ cm ^-3 . Next, using the epitaxial layer/wafer having the epitaxial film described above,
We created an orange light emitting diode and measured its brightness.

That is, the epitaxial wafer was vacuum-sealed in a high-purity quartz ampoule together with 25 mg of zinc arsenide ZnAs ₂ as a p-type impurity, and the impurity was diffused at a temperature of 720°C. The depth of the pn junction obtained was 4.3 μm from the surface. Next, the obtained epitaxial wafer was put into a device manufacturing line that included a backside (substrate) polishing process, an electrode forming process, and a wire bonding process to produce an orange light emitting diode chip.

Next, the light emitting diode chip (chip area size and pn junction area size are both 500 μm x 500 μm)
A current with a DC current density of 10 A/cm ² was applied to the chip, and the brightness value was measured under the condition that the chip was not coated with an epoxy resin.

As a result, it was found that the product of the present invention has an extremely superior high brightness value, approximately 1.8 times that of the conventional product, with an average peak emission wavelength of 632 nm and an average brightness value of 5200 Ft·L.

Comparative example (manufacture of GaAs _0.6 P _0.4 epitaxial wafer) Silicon (Si) is added as an n-type impurity at 1.0×10 ¹⁸ atoms/cm, and the crystallographic plane orientation is 2 from the (001) plane to the [110] direction. A single crystal substrate having a plane deviated by ±0.5° was prepared. GaAs single crystal substrate was the first
The thickness was originally 410μm, but after degreasing with an organic solvent, it was reduced to 360μm by mechanical-chemical polishing.
It became thick and thick.

Next, the polished GaAs single crystal substrate and the high-purity Ga-containing quartz boat were set at predetermined locations in a horizontal quartz epitaxial reactor with an inner diameter of 70 mm and a length of 1000 mm. Argon (Ar) was introduced into the epitaxial reactor to sufficiently replace and remove air, and then high-purity hydrogen gas (H ₂ ) was introduced as a carrier gas at 2500 c.c./min to stop the flow of Ar. We have started the heating process. After confirming that the temperatures of the Ga-containing quartz boat set region and the GaAs single crystal substrate set region were maintained at 830° C. and 750° C., respectively, vapor phase growth of a GaAs _0.6 P _0.4 epitaxial film was started.

First, prior to forming the GaAs _0.6 P _0.4 epitaxial layer, high-purity hydrogen chloride gas (HCl), which is an corrosive gas, was introduced for 5 minutes at a rate of 90 c.c. per minute.
The surface of the GaAs single crystal substrate was eroded. Next, the supply of HCl for substrate erosion was stopped, and a GaAs _0.6 P _0.4 epitaxial layer was formed.

That is, diethyl tellurium {(C ₂ H ₅ ) ₂ Te} gas diluted with H ₂ gas to a concentration of 10 ppm was introduced at 15 c.c./min in approximately the same direction as the substrate-eroding gas flow (HCl). HCl is introduced into Ga in the quartz boat at 18 c.c. per minute as a Group B component gas for forming an epitaxial layer, and GaCl is generated by reacting with Ga, while HCl is used as a Group B component gas for forming an epitaxial layer. The flow rate of hydrogen arsenide (AsH ₃ ) at a concentration of 10% diluted with H ₂ was from 336 c.c. per minute for the first 53 minutes.
304 c.c. and at the same time the flow rate of PH ₃ diluted with H ₂ to a concentration of 10% was increased from 0 c.c. to 32 c.c. per minute.
Continuously increased up to cc. AsH ₃ for next 27 minutes
The flow rate of GaAs _1-x P _x mixture was continuously decreased from ₃₀₄ c.c. to 252 c.c. Crystal rate change layer (x from 0 to 0.4
After that, a GaAs _1-x P _x (x=0.4) constant composition layer was formed. That is, for the next 60 minutes, the above (C ₂ H ₅ ) ₂ Te, HCl, AsH ₃ and
The formation of epitaxial wafers in which GaAs _0.6 P _0.4 constant composition layers were grown while introducing PH ₃ in fixed amounts of 15 c.c., 18 c.c., 252 c.c., and 80 c.c., respectively, was completed.

The total thickness of the mixed crystal ratio change layer of the obtained GaAs _0.6 P _0.4 mixed crystal epitaxial wafer was 30 μm on average, and
The rate of change in the mixed crystal percentage in the first 19.9 μm region was 57% of the average rate of change.

A light emitting diode was produced in the same manner as in Example 1 using the obtained GaAs _0.6 P _0.4 mixed crystal epitaxial wafer. Peak emission wavelength 655nm brightness without epoxy coating, DC current density 10A/cm ² , emission part diameter
It was 331 μm and 1200 Ft·L, which was 1.5 times that of conventional light emitting diodes.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional model diagram of a GaAs _1-x P _x mixed crystal epitaxial wafer. DESCRIPTION OF SYMBOLS 1... Single crystal substrate, 2... Mixed crystal ratio change layer, 3...
...Constant mixed crystal ratio layer.

Claims (1)

[Claims] 1 a single crystal substrate 1, a gallium phosphide arsenide mixed crystal ratio variable layer 2 formed on the substrate 1, and the layer 2
In the gallium phosphide arsenide mixed crystal epitaxial wafer formed on top of the gallium phosphide arsenide mixed crystal layer 3 having a constant mixed crystal content, the layer 2 includes at least one layer having a constant mixed crystal content. And, the rate of change of the above-mentioned mixed crystal percentage with respect to the thickness in a region corresponding to 1/10 to 3/4 of the total thickness of layer 2 from the interface between substrate 1 and layer 2 is A wafer characterized in that the rate of change of the mixed crystal percentage with respect to thickness is smaller than the average value of the rate of change with respect to the thickness of the wafer.