JPH0463040B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for vapor phase growth of an indirect transition type ternary compound semiconductor gallium arsenide phosphide (GaAs _1-x P _x ) epitaxial film for light emitting diodes. Conventional technology Conventionally, yellow light emitting diodes (center emission wavelength 5850
), orange light emitting diode (center emission wavelength 6300Å)
Epitaxial wafers for such applications include a GaP layer on a GaP single crystal substrate, and a GaAs _{1-x P} After epitaxially growing a layer with variable ratio x (hereinafter referred to as x variable layer) and obtaining a layer with a desired mixed crystal ratio x constant, epitaxial growth is continued with the mixed crystal ratio x, and at the same time a constant concentration of nitrogen is Add atoms. Then, a method is used in which epitaxial growth is stopped when the layer having a constant mixed crystal ratio x reaches a desired thickness. Light emitting diodes made from wafers using such a method did not provide satisfactory luminous intensity. A method for epitaxially growing a GaAs _1-x P _x film using this conventional method will be explained below with reference to the drawings. Second
Figure a shows a cross section of a GaAs _1-x P _x epitaxial wafer for yellow light emitting diodes, and Figure 2 b shows an example of its nitrogen concentration distribution. 11 is a GaP single crystal substrate with a thickness of about 300μ, 12
13 is a GaP epitaxial layer with a thickness of approximately 5 μm, and 13 is a crystal amorphous strain relaxation technique in which the mixed crystal ratio x is changed from 1 to approximately
x-varied layer with a thickness of about 35 μ varied to 0.85, 14
and 15 is a constant x layer where x keeps about 0.85.
However, 14 is a constant layer having a thickness of approximately 10 μm, and 15 is a constant layer having a thickness of approximately 25 μm to which nitrogen atoms are added. Problems to be Solved by the Invention However, in this method, nitrogen atoms are added to a desired concentration of GaAs _{1-x P} Therefore, the emission intensity was not necessarily satisfactory. Means for Solving the Problems The present invention aims to solve these drawbacks by solving the following facts (1): When nitrogen atoms are added to a GaAs _1-x P _x crystal, crystal defects rapidly increase in the initial stage of addition; , decreases as the growth reaction progresses, that is, as the epitaxial layer becomes thicker. (2) As the GaAs _1-x P _x epitaxial layer becomes thicker,
The difference in lattice constant between the GaP substrate and the SaAs _1-x P _x crystal increases the warpage of the epitaxial wafer and at the same time deteriorates the crystal quality of the epitaxial film, so there is a limit to the thickness of the epitaxial layer. This is what we arrived at as a result of various studies. It consists of gallium arsenide phosphide (GaAs _1-x
In a method for vapor phase growth of an epitaxial film consisting of _P ), and the addition of nitrogen atoms, which will become an isoelectronic trap, is started from any point in the layer consisting of the same component as the substrate and the mixed crystal ratio x variable layer. This is a method for growing a gallium phosphide arsenide epitaxial film, characterized in that the ratio x is set to a desired value near a conversion point of a constant layer. This will be explained in detail below with reference to the drawings. Figure 1a is for a yellow light emitting diode according to the present invention.
FIG. 1b shows an example of the nitrogen concentration distribution in a cross section of a GaAs _1-x P _x epitaxial wafer. 1 is a GaP single crystal substrate with a thickness of about 300 μm, 2 is a GaP epitaxial layer with a thickness of about 5 μm, 3 is an x-varied layer with a thickness of about 18 μm in which the crystallinity x is varied from 1 to about 0.9, and 4 is a mixed layer. An x-variable layer with a thickness of about 17μ in which the crystallinity x is changed from about 0.9 to about 0.85 and at the same time the nitrogen atoms are gradually increased from zero to the desired concentration. x constant layer of thickness approximately 30 μm doped to a concentration of . Nitrogen atoms may be added to the x-change layer 4 from the beginning or in the middle of the layer. As a result, the crystal quality is improved without increasing the thickness of the constant x layer, and the characteristics of the light emitting diode can be significantly improved. In the present invention, the value of x of the mixed crystal ratio x constant layer is
You can choose between 0.4 or more and less than 1, but if x
If it is less than 0.4, red light is emitted by a direct transition type light emitting mechanism, and no exciton light is emitted by isoelectronic traps, so there is no need to add nitrogen atoms. When the mixed crystal ratio x is in the range of 0.4 or more and less than 1, it is necessary to add nitrogen atoms, and without this, the light emitting intensity of the light emitting diode produced from now on will not be practically sufficient. In this way, the mixed crystal ratio x is set to 0.4 or more and 1
By selecting within the range below, the emission spectrum can be arbitrarily selected from red to green. Next, the present invention will be explained with reference to Examples and Comparative Examples, but the present invention is not limited to the Examples given here. EXAMPLE A GaAs _1-x P _x epitaxial wafer for a yellow light emitting diode having the structure shown in FIGS. 1a and 1b was manufactured by the following method. Tellurium (Te)
of crystal orientation <100> with addition of 2.5x10 ¹⁷ atoms/ ^cm3
A GaP single crystal rod was sliced to a thickness of approximately 350μ with a 5° deviation in the <110> direction from (100), and was then subjected to conventional chemical etching and mechanochemical polishing to a thickness of approximately 350μ.
A 300μ GaP mirror wafer was obtained and used as a substrate. In addition, the reaction gases include hydrogen (H ₂ ), hydrogen sulfide diluted with H ₂ at a concentration of 50 ppm (H ₂ S n-type impurity), 1% hydrogen arsenide (AsH ₃ ) diluted with H ₂ , and 10% diluted with H ₂ Hydrogen phosphide (PH ₃ ), high purity hydrogen chloride (HCl) and high purity ammonia gas (NH ₃ ) were used (hereinafter, the above gases were converted into H ₂ , H ₂ S/H ₂ , A
abbreviated as sH ₃ /H ₂ , PH ₃ /H ₂ , HCl and NH ₃ ). First, the cleaned GaP single crystal substrate and a quartz container containing high-purity Ga were set at a predetermined location in a vertical quartz reactor. After introducing high-purity nitrogen gas (N ₂ ) into the reactor, followed by high-purity hydrogen gas (H ₂ ) as a carrier gas to sufficiently replace the inside of the reactor, the temperature began to rise.
If the temperature of the above GaP substrate region reaches 880℃,
After holding the temperature for an additional 10 minutes, vapor phase growth of a GaAs _1-x P _x epitaxial film for a yellow light emitting diode was started using the following procedure. First, H ₂ S/H ₂ was introduced at a flow rate of 10 c.c. per minute, while HCl was introduced at a flow rate of 58 c.c. per minute to react with Ga in the quartz container to form GaCl. A GaP epitaxial layer 2 having a thickness of approximately 5 μm was grown on the GaP single crystal substrate 1 by simultaneously introducing PH ₃ /H ₂ at a flow rate of 250 c.c./min. Next, an x variable layer was epitaxially grown on the layer 2 by the following method. While initially maintaining the per minute flow rates of H ₂ S/H ₂ , HCl and PH ₃ /H ₂ at 10 c.c., 58 c.c. and 250 c.c., respectively, the flow rate of AsH ₃ /H ₂ was gradually changed from 0 c.c. to 170 c.c. per minute to form an x-variable layer 3 with a thickness of about 18 μm in which the mixed crystal ratio x varied from 1 to about 0.9.
The temperature of the substrate region was gradually decreased from 880<0>C to 820<0>C while the _AsH3 / _H2 flow rate was varied from 0 c.c. to 170 c.c. per minute. Thereafter, the temperature of this substrate region was fixed at 820° C. until the entire epitaxial film growth was completed. Next, the flow rates of H ₂ S/H ₂ , HCl and PH ₃ /H ₂ were adjusted per minute.
AsH ₃ /H ₂ while keeping at 10c.c., 58c.c. and 250c.c.
Gradually increase the flow rate from 170 c.c. to 260 c.c. per minute (during this time x changes from about 0.9 to about 0.85), and at the same time
The flow rate of NH ₃ was also gradually increased from 0 c.c. to 400 c.c. per minute, and a variable layer 4 having a thickness of about 17 μm was formed while increasing the amount of nitrogen added. Finally, the flow rates of H ₂ S/H ₂ , HCl, PH ₃ /H ₂ , AsH ₃ /H ₂ and NH ₃ were set to 10 c.c., 58 c.c., and 250 c.c. per minute, respectively.
A fixed layer 5 of approximately 30 μm in thickness is formed by adding nitrogen atoms to maintain the desired concentration N ₁ at 260 c.c. and 400 c.c.
GaAs _1-x P _x epitaxial film, i.e. GaAs _0.15
P _0.85 epitaxial film growth was completed. Comparative Example A yellow light emitting diode according to the prior art having the structure shown in FIGS. 2a and 2b was prepared by the following method.
GaAs _{1-x Px} epitaxial wafers were fabricated. A GaP epitaxial layer 12 and an x-change layer 13 are formed on a GaP single crystal substrate 11 using the same method as in the example.
(corresponds to Examples 3 and 4. However, nitrogen atoms are not added.) After growing H ₂ S/H ₂ ,
The flow rates of HCl, PH ₃ /H ₂ and AsH ₃ /H ₂ were fixed at 10 c.c., 58 c.c., 250 c.c. and 260 c.c. per minute, respectively, and the thickness of approximately 10μ was constant. Layer 14 was grown. Finally H ₂ S/
The flow rate _of NH ₃ was maintained at 10 _c.c. , 58 _c.c. , 250 c.c. and 260 _c.c. per minute, respectively _. Increased from 0 c.c. to 400 c.c. per minute,
Then, the flow rates of H ₂ S/H ₂ , HCl, PH ₃ /H ₂ , AsH ₃ /H ₂ and NH ₃ were set to 10 c.c., 58 c.c., and 250 c.c. per minute, respectively.
and fixed at 260 c.c. and 400 c.c., add nitrogen atoms to a desired concentration of N ₂ to form a nitrogen-doped x constant layer 15 with a thickness of about 25 μm, and form an indirect transition type for yellow light emitting diode.
GaAs _0.15 P _0.85 epitaxial wafers were manufactured. Next, Zn was diffused into the epitaxial wafer for a yellow light emitting diode obtained by the method shown in the above Examples and Comparative Examples to form a P-N junction.
I made a yellow light emitting diode. The luminance (millicandela mcd) of the yellow light emitting diodes (without resin coating) obtained in Examples and Comparative Examples thus obtained were as shown in the following table.

[Table] Average values.
The case where gallium phosphide (GaP) is used as the substrate has been described above, but gallium arsenide (GaAs) may also be used. Effects of the invention As shown in the table, the results obtained by the method of the present invention
Light-emitting diodes using GaAs _1-x P _x epitaxial films achieved about 30% brightness improvement compared to conventional methods. Therefore, the wafer having the GaAs _1-x P _x epitaxial film manufactured according to the present invention is industrially useful as a material for light emitting diodes.

[Brief explanation of drawings]

Figure 1a is for a yellow light emitting diode according to the present invention.
A cross-sectional view illustrating a GaAs _1-x P _x epitaxial wafer, FIG. 1b shows an explanatory diagram showing the nitrogen concentration distribution of the wafer, _{and FIG.} FIG. 2b, which is a cross-sectional view of _{an x-} epitaxial wafer, is an explanatory diagram showing the nitrogen concentration distribution of the wafer. 1, 11... GaP single crystal substrate, 2, 12... GaP epitaxial layer, 3, 13... x variable layer, 4... nitrogen-doped x variable layer, 14... x constant layer, 5, 15... nitrogen-doped x constant layer, N ₁ , N ₂ ... Desired nitrogen concentration value.

Claims (1)

[Claims] 1. A method for growing an epitaxial film made of gallium phosphide arsenide (GaAs _{1-x P} At the same time, the layer consisting of the same component as the substrate and the layer with the same composition as the substrate are grown in the following order: a layer with variable crystal content x, a layer with constant mixed crystal content x (however, 0.4≦x<1). Gallium arsenide phosphide characterized by starting from an arbitrary point in the mixed crystal ratio x variable layer and adjusting to a desired value near the conversion point between the mixed crystal ratio x variable layer and the mixed crystal ratio x constant layer. Method of growing epitaxial films. 2. The method according to claim 1, characterized in that nitrogen atoms are added gradually to a desired concentration. 3. The method according to claim 1 or 2, characterized in that the single crystal substrate is selected from gallium phosphide (GaP) or gallium arsenide (GaAs).