JPH06268256A - Manufacture of light emitting diode epitaxial wafer - Google Patents

Abstract

PURPOSE:To enable light emitted from a light emitting diode to be sent out efficiently by a method wherein specific single crystals each possessed of a P-N junction are successively grown in layers on a GaP single crystal substrate. CONSTITUTION:An epitaxial initial layer 2 is grown on a GaP substrate 1, and successively an N-type grading layer 3 is formed. A nitrogen-free N-type GaAs1-xPx (0.4<=X<=0.9) layer is grown to serve as a relaxation layer 4 so as to relax defects in the grading layer 3. Then, a nitrogen-loaded N-type GaAs1-xPx(0.4<=X<=0.9) epitaxial single crystal layer is grown as a light emitting layer 5. In succession, a nitrogen-loaded P-type GaAs1-xPx (0.4<=X<=0.9) epitaxial single crystal layer doped with zinc is grown to serve as a low concentration P-type light emitting layer 6. Thereafter, a nitrogen-free P-type GaAs1-xPx (0.4<=X<=0.9) layer is grown so as to serve as a high concentration P-type injection layer 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a GaAs ₁ -xPx vapor phase epitaxial wafer for obtaining a light emitting diode.

[0002]

2. Description of the Related Art A light emitting diode made of GaAs ₁ -xPx is widely used as a display device because it can emit red light to green light by changing the mixed crystal ratio X. These light emitting diodes use an epitaxial wafer grown by either a liquid phase method or a vapor phase method.

According to the above liquid phase method, a relatively bright light emission output, that is, a light emission diode with high brightness can be obtained, but only an epitaxial crystal having a lattice constant of a crystal substrate can be obtained. Therefore, a light emitting diode that emits an intermediate color such as orange or yellow cannot be obtained.

On the other hand, in the case of using the vapor phase method, a gray layer is provided between the substrate and the light emitting layer, in which crystal layers having different composition ratios are sequentially provided.
Although it is possible to obtain an epitaxial crystal that does not match the lattice constant of the crystal substrate by applying a technique called ding, on the other hand, it is very difficult to obtain a desirable PN junction because the PN junction must be formed by the thermal diffusion method. As a result, a light emitting diode having higher brightness than the liquid phase method cannot be obtained.

As a solution to the problems of the conventional liquid phase method, the present inventor has proposed the following method for producing an epitaxial wafer for a light emitting diode. The partial pressure of Ga component and the partial pressure of phosphorus and arsenic components during the epitaxial growth of N-type GaAs _1- xPx containing nitrogen atoms are 0.00
P-type GaAs with nitrogen atom of 3 to 0.02 atm ₁
The partial pressure of Ga component and the partial pressure of phosphorus and arsenic component of -xPx epitaxial growth are set to 0.01 to 0.05 atm (see Japanese Patent Laid-Open No. 4-328823). On the N-type GaAs _1- xPx epitaxial single crystal layer containing nitrogen atoms, a low-concentration N-type GaAs _1- xPx epitaxial single crystal layer containing nitrogen atoms and substantially not doped with N-type impurities is grown. P type with nitrogen atom and zinc doped
A GaAs _1- xPx epitaxial single crystal layer is grown (see Japanese Patent Laid-Open No. 4-328878). Both of the above can obtain a light emitting diode having high brightness with a very high quality PN junction by vapor phase epitaxial growth.

[0006]

However, in the above-mentioned conventional example, the P-type impurities are diffused into the low-concentration N-type layer from the P-type epitaxial layer grown on the low-concentration N-type layer which is not doped. Overcompensation occurred and there was a problem in reproducibility.

The present invention is intended to solve the problems of the prior art. A PN junction is formed without causing excessive compensation during vapor phase epitaxial growth, and the emitted light can be extracted to the outside very efficiently. It is another object of the present invention to provide a method of manufacturing an epitaxial wafer for a light emitting diode such as orange and yellow.

[0008]

That is, according to the present invention, GaAs _1- xPx (where, 0.
4 ≦ X ≦ 0.9) A method for manufacturing an epitaxial wafer for a light emitting diode in which a single crystal layer is epitaxially grown in a vapor phase, in a low concentration N type epitaxial single crystal containing nitrogen atoms on an N type epitaxial single crystal layer not containing nitrogen atoms. A layer, a low-concentration P-type epitaxial single crystal layer containing nitrogen atoms, and a high-concentration P-type epitaxial single crystal layer not containing nitrogen atoms are sequentially grown in a laminated form. In the present invention, low concentration means 2 × 10 ¹⁶ pieces /
cm ³ or less means high concentration and 2 × 10 ¹⁷ pieces / cm ³ or more.

[0009]

By growing the low-concentration P-type epitaxial single crystal layer 5 on the low-concentration N-type epitaxial single crystal layer 5, the concentration difference between the N-type and the P-type is reduced, and excess compensation caused by such concentration difference is avoided. You can In addition, GaAs _1- xPx containing nitrogen atom which is an isoelectronic wrap
The wavelength energy of the light emitting diode is about 80 meV or more lower than the wavelength energy of the GaAs _1- xPx light emitting diode that does not contain nitrogen atoms in the single crystal layer. In short, the energy of the emission wavelength is GaAs _1- xPx bandgap energy −
It is about 80 meV lower. On the other hand, the light absorption coefficient increases as the mixed crystal ratio X decreases, in other words, the absorption coefficient is smaller in the case of not containing nitrogen atoms than in the case of containing nitrogen atoms. Therefore, when the light emitted from the PN junction is extracted to the outside, a larger film thickness is more efficient in the epitaxial film having a small absorption coefficient because of absorption in the epitaxial film and reflection and refraction on the surface. That is, the film thickness necessary for efficiently extracting the light emitted from the PN junction to the outside is obtained by growing the high-concentration P-type epitaxial single crystal layer 7 containing no nitrogen atom on the upper layer of the low-concentration P-type epitaxial single crystal layer 6. By forming it, it is possible to obtain a light emitting diode with high brightness equivalent to that of the liquid phase method.

[0010]

EXAMPLES Examples of the present invention will be shown below, but the present invention is not limited thereto.

Example 1 FIG. 1 shows an epitaxial wafer for a light emitting diode produced in Example 1, in which 1 is an N-type G
aP single crystal substrate, 2, 3, 4, 5, 6, and 7 are epitaxial initial layers, N-type grading layers, relaxation layers, N-type light-emitting layers, and P-types, which are sequentially stacked on the single crystal substrate 1. A light emitting layer and a P-type injection layer are shown respectively.

Next, the light emitting diode of the present invention will be described with reference to FIG.
The method for manufacturing the epitaxial wafer for a wafer will be described in more detail. First, a vertical quartz reaction tube having an inner diameter of 150 mm and a length of 140 cm was polished as an N-type GaP single crystal substrate to a thickness of 250 μm, a diameter of 2 inches, and a carrier concentration of 5 × 1.
Fourteen N ¹⁷ Ga ^-3 N-type GaP substrates 1 were installed, and liquid metallic gallium was housed in a quartz container upstream of the gas flow direction in the reaction tube. Then, after purging the inside of the reaction tube with the nitrogen gas flow rate of 10 l / min for about 30 minutes, the hydrogen gas flow rate of 8 l / min was applied until the metallic gallium was 830 ° C. and the substrate was 850 ° C. It was heated in an electric furnace. Then, 220 cc / min of hydrogen chloride gas for transferring metallic gallium in the quartz container, 60 cc / min of hydrogen sulfide gas diluted to 100 ppm with nitrogen gas as N-type dopant, and 120 cc / min of phosphine gas. Each was introduced into this reaction tube at a flow rate, and a 3 μm epitaxial initial layer 2 was grown for 20 minutes to form, and then arsine gas was increased at a rate of 0 cc / min to 0.73 cc / min for 90 minutes of grading. 27μ
An m-type N-type grading layer 3 was produced. When 90 minutes have passed since the formation of this graded layer, the above arsine gas has a flow rate of 66 cc / min.
It was continuously introduced into the reaction tube at a fixed amount. After the grading layer 3 is formed as described above, this grading layer 3
In order to alleviate defects in the daying layer 3, an N-type GaAs ₁ -xPx layer containing no nitrogen atoms was grown for 60 minutes in the above atmosphere to form a 12 μm relaxing layer 4.

Then, in order to add nitrogen acting as an isoelectronic trap into the epitaxial single crystal, epitaxial growth is carried out for 60 minutes while introducing ammonia gas at a rate of 350 cc / min together with the above atmosphere, whereby nitrogen atoms are removed. Including N-type GaAs ₁
An -xPx layer epitaxial single crystal layer was formed as a low-concentration N-type light emitting layer 5 of 12 μm. Subsequently, dimethylzinc, which is a P-type dopant, was introduced at a rate of 4 cc / min together with the above-mentioned atmosphere, and epitaxial growth was performed for 40 minutes with ammonia gas to obtain a P-type doped with zinc containing nitrogen atoms. An GaAs _1- xPx layer epitaxial single crystal layer was formed as a low-concentration P-type light emitting layer 6 of 8 μm.
After that, the ammonia gas was stopped, and the P-type GaAs _1- xPx layer doped with zinc containing no nitrogen atom was increased to a rate of 50 cc / min of the dopant and epitaxially grown for 40 minutes to obtain a high concentration P of 8 μm. The mold injection layer 7 was formed.

In order to fabricate a light emitting diode using this epitaxial wafer, Be containing 1% Au on the surface of the epitaxial layer and 1 on the back surface of the GaP substrate were prepared.
Ge containing 2% Au was vapor-deposited and maintained in hydrogen gas at 450 ° C. for 10 minutes for alloying.
A chip of 0 μm square was formed, which was connected to a lead frame and resin-sealed to form a light emitting diode element having a diameter of 5 mm. When the emission brightness of the light emitting diode element was measured, when the operating current was 20 mA, the emission wavelength was 630 nm,
The brightness was 620 mcd. This is a wavelength 63 generated by thermally diffusing zinc on the epitaxial surface of the conventional N-type GaAs _1- xPx layer obtained by the vapor phase epitaxial growth method.
The brightness is extremely high, which is about 2.3 times that of a 0 nm orange light emitting diode.

Example 2 P-type GaAs ₁ -xPx layer containing no nitrogen atom, high concentration P
Only the film thickness of the mold injection layer 7 is 4 μm, 6 μm, 8 μm, 12 μm
Epitaxial growth was performed to m, 18 μm, 24 μm, and 30 μm, and the other layers were epitaxially grown to the same film thickness under the same conditions as in Example 1 above. Then, the emission luminance of the obtained light emitting diode was measured. The measurement result is shown in FIG.

As is clear from FIG. 2, as the film thickness of the high-concentration P-type implantation layer 7 becomes thicker, the brightness becomes higher and the film thickness becomes 1
When it exceeds 8 μm, the brightness is not increased, and the measured values are almost the same. From FIG. 2, it can be understood that when the film thickness of the high-concentration P-type injection layer 7 exceeds 6 μm, a suitable brightness as a light emitting diode can be obtained, and when it is less than that, it is insufficient. .

Example 3 P-type GaAs _1- xPx layer epitaxial single crystal containing nitrogen atoms and doped with zinc was doped with only low-concentration P-type light-emitting layer 6 having a thickness of 4 μm, 5 μm, 8 μm, 12 μm, and 18 μm. The other layers were epitaxially grown to the same film thickness under the same conditions as in Example 1 above.
Then, the light emission luminance of the obtained light emitting diode was measured, and the result is shown in FIG.

As is apparent from FIG. 3, it is shown that the brightness increases as the film thickness of the P-type light emitting layer 6 increases, and conversely the brightness gradually decreases when the film thickness exceeds 8 μm. From FIG. 3, the thickness of the P-type light emitting layer 6 is 5 μm.
It can be understood that when it exceeds m, a suitable brightness as a light emitting diode can be obtained, and when it is less than that, it is insufficient. The total thickness of the low-concentration P-type light emitting layer 6 and the high-concentration P-type injection layer 7 is 12 μm based on the above measurement results.
The above is desirable.

[0019]

Since the present invention is configured as described above, the low-concentration P-type GaAs _1- xPx layer containing nitrogen containing zinc is a lower layer of the low-concentration N-type GaAs _1- xPx.
Not only is it possible to reliably avoid overcompensation caused by diffusion into the layer epitaxial single crystal layer 5, but also absorption due to a decrease in absorption coefficient caused by the fact that the energy of the emission wavelength is lower than the band gap energy of GaAs _1- xPx. Light can be extracted very efficiently by thickening the epitaxial film having a small coefficient. As a result, the conventional defect that the brightness is lower than that of the light emitting diode obtained by the liquid phase method can be solved, and in particular, a high brightness light emitting diode of an intermediate color such as orange or yellow is manufactured by the gas phase method. It has a special effect of being able to do.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an epitaxial wafer manufactured according to a first embodiment of the present invention.

FIG. 2 is a graph showing the results of measuring the emission brightness of the epitaxial wafers manufactured on the P-type implantation layers 7 having different film thicknesses according to Example 2.

FIG. 3 is a graph showing the results of measuring the emission luminance of the epitaxial wafers manufactured on the P-type light emitting layers 6 having different film thicknesses according to Example 3.

[Explanation of symbols]

 1 GaP single crystal substrate 2 Epitaxial initial layer 3 N type grading layer 4 Relaxation layer 5 N type light emitting layer 6 P type light emitting layer 7 P type injection layer

Claims (4)

[Claims] 1. A GaA having a PN junction on a GaP single crystal substrate.
In a method for manufacturing an epitaxial wafer for a light emitting diode, in which a single crystal layer of s ₁ -xPx (where 0.4 ≦ X ≦ 0.9) is vapor-phase epitaxially grown, nitrogen atoms are not added to the N-type epitaxial single crystal layer containing no nitrogen atom. Low-concentration N-type epitaxial single crystal layer containing nitrogen, low-concentration P-type epitaxial single crystal layer containing nitrogen atoms, and high-concentration P containing no nitrogen atoms
A method for manufacturing an epitaxial wafer for a light emitting diode, which comprises sequentially growing a type epitaxial single crystal layer in a layered manner. 2. The method for producing an epitaxial wafer for a light-emitting diode according to claim 1, wherein the film thickness of the low-concentration P-type epitaxial single crystal layer containing nitrogen atoms is 5 μm or more. 3. The method for producing an epitaxial wafer for a light emitting diode according to claim 1, wherein the high-concentration P-type epitaxial single crystal layer containing no nitrogen atoms has a film thickness of 6 μm or more. 4. The total thickness of the low-concentration P-type epitaxial single crystal layer containing nitrogen atoms and the high-concentration P-type epitaxial single crystal containing no nitrogen atoms is 12 μm or more. A method for manufacturing an epitaxial wafer for a light emitting diode as described above.