JPH0219619B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for vapor phase growth of a compound semiconductor epitaxial film comprising elements of Groups and Groups of the Periodic Table, which is suitable for manufacturing light emitting diodes, particularly green light emitting diodes.

Green light emitting diodes are made of gallium phosphide (GaP), gallium aluminum phosphide (Gal-
x AlxP, 0≦x≦1), etc. However, when the epitaxial film is grown by vapor phase growth method, compared to when it is grown by liquid phase growth method. As a result, the luminance of the light emitting diode obtained was low. However, compared to liquid phase growth, vapor phase growth provides a smoother epitaxial film surface, and the cleavage plane is perpendicular to the substrate surface (100).
It is known that this method has the advantage that a square chip can be obtained, which is suitable for the production of light emitting diodes because a surface can be used.

The present inventors solved the problems of the above-mentioned vapor phase growth method and developed an epitaxial film made of gallium phosphide or gallium aluminum phosphide, which is suitable for manufacturing high-brightness green light emitting diodes, by vapor phase growth. As a result of extensive research, the present invention was arrived at.

An object of the present invention is to provide a method for vapor phase growth of epitaxial films suitable for manufacturing high-brightness green light-emitting diodes.

The above purpose is to create a compound (hereinafter referred to as “-
"family compounds". ) A method for vapor phase growth of a semiconductor epitaxial film, in which the temperature of a single crystal substrate is continuously lowered, and at the same time, the amount of nitrogen source supplied to the single crystal substrate is continuously reduced to grow the epitaxial film in the epitaxial film. This is achieved by keeping the nitrogen concentration approximately constant.

As the single crystal substrate used in the present invention, the (100) plane of gallium phosphide or a plane having a deviation of within about 5° from the (100) plane does not require correction of the deviation of the lattice constant, and the surface state can be improved. Although this is most suitable because a good epitaxial film can be obtained, substrates cut from single crystals of other - group compounds, silicon, germanium, sapphire, spinel, etc. can also be used.

Further, the composition of the epitaxial growth gas may be a usual one, for example, Ga/HCl/PH ₃ /H ₂ ,
Ga( _CH3 ) ₃ / _PH3 / _H2 , Al( _C2H5 ) ₃ / _Ga
(CH ₃ ) ₃ /PH ₃ /H ₂ etc. are used. in this case,
H ₂ S, (C ₂ H ₅ ) ₂ Te, etc. are added as n-type impurities, and (C ₂ H ₅ ) ₂ Zn, (C ₂ H ₅ ) ₂ Cd, etc. are added as p-type impurities.

Since gallium phosphide is an indirect transition type, nitrogen is added as an isoelectronic trap to improve brightness.

In this case, a nitrogen compound such as NH ₃ or NH ₂ (CH ₃ ) is used as the nitrogen source.

During vapor phase growth of an epitaxial film, the temperature of the substrate is initially set at about 900 to 950°C, and then continuously lowered to about 700 to 770°C. When forming a p-n junction by adding the above p-type impurity, for example Zn, if the substrate temperature is high, the p-type impurity will diffuse to the n-side and a good p-n junction cannot be obtained, so it is necessary to lower the substrate temperature. There is. In that case, if the temperature is changed rapidly, the crystallinity of the epitaxial film deteriorates, so it is necessary to lower the temperature continuously. In this case, the temperature drop is from 1℃/min to 7℃/min.
About a minute is appropriate. Note that the rate of temperature decrease does not need to be kept constant and may be varied within the above rate range.

Further, when the substrate temperature is lowered, the concentration of nitrogen in the epitaxial film increases, but in this case, problems such as an increase in the amount of light absorption and a deterioration of the crystallinity of the epitaxial film occur. Therefore, it is necessary to keep the nitrogen concentration constant by decreasing the amount of nitrogen source such as ammonia supplied as the substrate temperature decreases.
The concentration of nitrogen is usually selected to be 10 ¹⁸ /cm ³ or higher.

A pn junction is formed by switching between an n-type impurity and a p-type impurity during epitaxial growth. There is a layer with low nitrogen concentration in the carrier's radiative recombination region centered around this p-n junction, e.g.
By forming one or more layers of 10 ¹⁷ /cm ³ or less, the peak emission wavelength can be made 570 nm or less without reducing brightness. Furthermore, if the addition of nitrogen is stopped after the epitaxial film is grown to a thickness that is at least the diffusion distance of minority carriers from the p-n junction, the light emitted by the p-n bond can be extracted to the outside without attenuation.

In the method of the present invention, since the pn junction is formed during epitaxial growth, the position and depth of the pn junction can be confirmed, so the above operations can be easily performed.

When using gallium aluminum phosphide,
It emits a deeper green color than gallium phosphide, which emits light at wavelengths of 560 nm or shorter.

The brightness of the light emitting diode manufactured using the epitaxial film obtained by the method of the present invention is comparable to or higher than that of the liquid phase growth method, and considering the characteristics of the vapor phase growth method, It has great utility value.

Next, a more specific explanation will be given based on an example.

〔Example〕

In a horizontal vapor phase epitaxial reactor, the crystallographic plane orientation of the metallic Ga and surface is < with respect to the (100) plane.
An n-type GaP single crystal substrate tilted at 4° in the 110> direction was installed.

The temperature of the metal Ga installation area was increased to 770°C, and the temperature of the substrate installation area was increased to 910°C while flowing hydrogen at 2/2.

After the temperature of the reactor reaches the set value, 35 ml/min of _H2S diluted with nitrogen gas to a concentration of 40 ppm, 80 ml/min of HCl for Ga transport, and PH diluted to a concentration of 12% with hydrogen gas. ₃ was introduced at 320 ml/min, and an n-type GaP single crystal region was grown by vapor phase epitaxial growth for the first 10 minutes.

From 910°C to 750°C over the next 80 minutes, following a pre-programmed temperature drop profile.
The temperature of the substrate installation part was lowered to .degree. C., and the introduction of _NH.sub.3 gas was started after the first 10 minutes of the above 80 minutes had elapsed.

The amount of NH ₃ gas introduced was initially 167 ml/min, and in this case, the nitrogen concentration in the epitaxial film was 8×
10 ¹⁸ /cm ³ . After a further 40 minutes had elapsed, the supply of H ₂ S was stopped, and introduction of (C ₂ H ₅ ) ₂ Zn diluted with hydrogen gas to a concentration of 300 ppm was started at a rate of 32 ml/min.

Thereafter, the p-type GaP single crystal region was grown in the vapor phase during the remaining 30 minutes, completing the entire epitaxial growth process. The flow rate of NH ₃ gas introduced at the end of epitaxial growth was 31 ml/min according to the program.

The thickness of the n-type region to which nitrogen was not added in the obtained GaP epitaxial film was 12 μm, the thickness of the n-type region to which nitrogen was added was 28 μm, and the thickness of the p-type region was 23 μm.

Regarding the carry concentration, nitrogen added n
The average density was 1×10 ¹⁶ cm ^-3 in the type region, and 5×10 ¹⁷ cm ^-3 in the nitrogen-doped p-type region.

The nitrogen concentration was uniform in both the n-type and p-type regions to which nitrogen was added, and was 8.1×10 ¹⁸ cm ⁻³ on average.

As described above, manufactured according to the present invention
A green light emitting diode with a chip size of 350 μm x 350 μm was cut out from a GaP epitaxial wafer (the brightness at the peak emission wavelength of 566.8 nm was an average of 11000 Ft・L without an epoxy resin coating and under the conditions of a current density of 20 A/cm ^{2 )} . Ta.

This value is the average luminance value of a conventional vapor-phase grown green light emitting diode with a p-n junction formed by the diffusion method measured under the same conditions as 2500Ft・L. Average brightness value of vapor grown green light emitting diode
It far surpassed the 7500Ft/L.

Claims (1)

[Claims] 1 Nitrogen is added on a single crystal substrate, and pn
In a method for vapor phase growth of a compound semiconductor epitaxial film made of elements of Groups and Groups of the Periodic Table in which a junction is formed, the temperature of the single crystal substrate is continuously lowered, and at the same time the temperature of the single crystal substrate of the nitrogen source is lowered. A method characterized in that the nitrogen concentration in the epitaxial film is kept approximately constant by continuously decreasing the amount of nitrogen supplied to the epitaxial film. 2. The method according to claim 1, wherein the compound semiconductor is gallium phosphide.