JPH1197740A - Epitaxial wafer for gap light emitting diode and gap light emitting diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a GaP light emitting diode of high luminance. SOLUTION: This light emitting diode is formed of an epitaxial wafer for a GaP light emitting diode in which a PN junction is formed by laminating at least one N-type GaP epitaxial layer and at least one P-type GaP epitaxial layer on a GaP single crystal substrate. In this case, the dislocation density (EPD) of the GaP single crystal substrate described above is at most 3×10<-3> cm<-3> , the dopant of the GaP single crystal substrate is tellurium(Te) or silicon(Si), and the concentration of sulfur (S) in the GaP single crystal substrate is at most 5×10<16> cm<-3> .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an epitaxial wafer for a GaP light-emitting diode and a GaP light-emitting diode, and more particularly to an epitaxial wafer for a GaP light-emitting diode for providing a high-brightness light-emitting diode and a wafer manufactured from the epitaxial wafer. It relates to a GaP light emitting diode.

[0002]

2. Description of the Related Art As GaP light emitting diodes, there are three kinds of light emitting diodes of yellow green, pure green and red, all of which are manufactured by a liquid phase epitaxial growth method. Since GaP is a crystal having an indirect transition type band structure, the luminance of yellow-green and red light-emitting diodes is increased by introducing an impurity serving as a light emission center into the crystal.

A yellow-green light-emitting diode is formed by forming an n-type GaP buffer layer on an n-type GaP single crystal substrate as needed, then n-type GaP epitaxial layer, and n-doped n (N) as a light emission center. It has a p-type GaP epitaxial layer and a p-type GaP epitaxial layer, and emits yellow-green light having an emission wavelength of about 570 nm. The pure green light-emitting diode is formed by forming an n-type GaP buffer layer on an n-type GaP single crystal substrate as needed, and then n-type GP not doped with a light-emitting center impurity such as nitrogen (N).
Since it has an aP epitaxial layer and a p-type GaP epitaxial layer and does not use a light emission center, it emits pure green light having an emission wavelength of about 555 nm although its luminance is lower than that of the above-mentioned yellow-green light-emitting diode. The red light emitting diode is formed on an n-type GaP single crystal substrate by n-type GaP.
It has a structure in which a P epitaxial layer and a p-type GaP epitaxial layer doped with zinc (Zn) and oxygen (O) are formed. A Zn-O pair in the p-type GaP epitaxial layer serves as an emission center, and an emission wavelength of about 700 nm. Emit red light.

[0004] Generally, these GaP light emitting diodes are:
It is manufactured using an n-type GaP single crystal substrate obtained from an n-type GaP single crystal grown by liquid sealing Czochralski method (LEC method) using Te, Si or the like as a dopant.

[0005]

Although the luminance of these GaP light emitting diodes has been improved by recent technological improvements, the market is demanding higher luminance. An object of the present invention is to provide a GaP light emitting diode with high brightness.

[0006]

According to the present invention, a pn junction is formed by laminating at least one n-type GaP epitaxial layer and at least one p-type GaP epitaxial layer on a GaP single crystal substrate. In the epitaxial wafer for a GaP light emitting diode and a GaP light emitting diode manufactured from the epitaxial wafer, the dislocation density (EPD) of the GaP single crystal substrate is 3
× 10 ³ cm ^-2 or less, and the dopant of the GaP single crystal substrate is tellurium (Te) or silicon (Si).
And the sulfur (S) concentration in the GaP single crystal substrate is 5 × 10 ¹⁶ cm ⁻³ or less. It is more preferable that the dislocation density of the GaP single crystal substrate is 1 × 10 ³ cm ⁻² or less. It is more preferable that the concentration of sulfur in the GaP single crystal substrate is 2 × 10 ¹⁶ cm ⁻³ or less. The above-described GaP single crystal substrate can be manufactured from a GaP single crystal grown by a vertical boat method.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Conventionally, an n-type GaP single crystal substrate obtained from an n-type GaP single crystal grown by a liquid-sealed Czochralski method (LEC method) has been used as a substrate for a GaP light-emitting diode. Was. However, the GaP single crystal substrate grown by the LEC method has a disadvantage that the dislocation density (EPD) is large. Even if the EPD is reduced by optimizing the growth conditions, the EPD of the GaP single crystal substrate can be reduced to 1 × 10 It was difficult to make it less than ⁴ cm ^-2 . Here, the EPD of the GaP single crystal substrate
Is a point on the straight line passing through the center of the single crystal substrate,
It is the average value of EPD measured for a total of 9 points, 4 points at 5 mm intervals on both sides from the center.

In recent years, in growing single crystals of InP, GaAs, etc., VB (vertical bridge) has been used.
man) method, LEVB (liquid encapsu)
lated vertical bridgeman)
Method or VGF (vertical gradient)
The vertical boat method such as the nt freezing method
A single crystal having a lower EPD as compared with the LEC method can be obtained. Here, the vertical boat method means that in a single crystal growing furnace, a seed crystal is arranged below the single crystal raw material, and the single crystal raw material is melted and brought into contact with the seed crystal, and then upward from the seed crystal side. A single crystal growing method for growing a single crystal is generally called.

Therefore, the present inventors conducted single crystal growth on GaP by the above-mentioned vertical boat method, and found that EPD was 3 × 1.
A GaP single crystal substrate of not more than 0 ³ cm ^-2 was obtained.

Here, Si or Te was used as the n-type dopant of the GaP single crystal. Si or Te
When is used as a dopant, it is relatively easy to control the carrier concentration of the GaP single crystal. Conventionally, Ga
In some cases, S was used as the n-type dopant of the P single crystal, but in an epitaxial wafer for a GaP light emitting diode, as described later, S in a GaP single crystal substrate was taken into the epitaxial layer and the luminance of the GaP light emitting diode was increased. Therefore, it is not preferable to use S as the n-type dopant.

When a GaP light emitting diode was fabricated using an n-type GaP substrate fabricated from a GaP single crystal grown by the vertical boat method described above, the luminance was higher than that of a light emitting diode fabricated using a conventional LEC method GaP substrate. It turned out to be. The GaP substrate grown single crystal by the above vertical boat method and the Ga grown single crystal by the conventional LEC method
FIG. 1 shows the relationship between the EPD and the luminance of a GaP substrate of a yellow-green light emitting diode manufactured by the same process using a P substrate.

In FIG. 1, .largecircle. Indicates a vertical boat method GaP substrate, and .circle-solid. Indicates an LEC method GaP substrate. From FIG. 1, GaP
It is clear that the light emitting diode has high brightness when the EPD of the substrate is 3 × 10 ³ cm ⁻² or less, more preferably 1 × 10 ³ cm ⁻² or less.

However, even when a light emitting diode is manufactured using a GaP substrate of the same degree of EPD manufactured by the vertical boat method, variations in luminance sometimes occur depending on the production lot of the GaP single crystal. Then, when the relationship between various characteristics and luminance of the GaP substrate manufactured by the vertical boat method was investigated, it was found that there was a correlation between the sulfur (S) concentration in the GaP substrate and the luminance.

FIG. 2 shows the relationship between the S concentration in the GaP substrate and the luminance of the yellow-green light-emitting diode when a GaP substrate having an EPD of 3 × 10 ² cm ⁻³ is used. As shown in FIG. 2, by setting the S concentration in the GaP substrate to 5 × 10 ¹⁶ cm ⁻³ or less, more preferably 2 × 10 ¹⁶ cm ⁻³ or less,
High-brightness light emitting diodes can be obtained stably.

The reason why there is a correlation between the S concentration in the GaP substrate and the luminance of the light emitting diode is that when the S concentration in the GaP single crystal substrate is high, a part of S in the substrate during liquid phase epitaxial growth. Is taken into the epitaxial layer, and this taken-in S seems to be involved in the formation of the non-light-emitting process, but the details are unknown. Note that S was not added intentionally in the growth of the GaP single crystal, but during the growth of the GaP single crystal or in the synthesis of the GaP polycrystal as a raw material of the single crystal, S was slightly changed as a trace impurity in GaP. It seems to be mixed in. S
Since the segregation coefficient is very large, the S concentration in the single crystal becomes high even if a very small amount of the S source is present. As a result of various studies on the reduction of a small amount of S impurities unintentionally mixed, the present inventors have found that sulfur oxides in the air are a major pollution source. As a result, it was possible to reduce the S concentration in the single crystal by reducing the sulfur oxide in the air.

Although the present invention has been described based on the case of a GaP yellow-green light emitting diode, similar results were obtained for a GaP pure green light emitting diode and a GaP red light emitting diode. That is, the EPD is 3 × 10
Si-doped or Te-doped n having a concentration of ³ cm ^-2 or less, more preferably 1 x 10 ³ cm ^-2 or less, and an S concentration of 5 x 10 ¹⁶ cm ^-3 or less, more preferably 2 x 10 ¹⁶ cm ^-3 or less By using a GaP single crystal substrate, high brightness G
An aP light emitting diode was obtained.

[0017]

【Example】

(Example 1) First, an n-type GaP single crystal was grown by the LEVB method. FIG. 3 is a schematic cross-sectional view of the single crystal growing furnace used for the LEVB method. Seed crystal 2 and raw material G in crucible 1
The aP polycrystal 3 and B ₂ O ₃ 4 were charged and set in a single crystal growing furnace. After the inside of the furnace was replaced with gas, the inside of the furnace was set to a predetermined pressure with nitrogen gas, and GaP polycrystal 3 as a raw material and B ₂ O ₃
After melting of No. 4, a part of the seed crystal was melted for seeding, and the crucible was moved under a predetermined temperature distribution to grow a GaP single crystal. Note that Si was used as a dopant, and the carrier concentration was adjusted to 2 × 10 ¹⁷ cm ⁻³ . In addition, in order to prevent the incorporation of S into the single crystal, thorough measures were taken to reduce S in all steps from the synthesis of the raw material GaP polycrystal to the growth of the single crystal. The S concentration in the obtained GaP single crystal was 3 × 10 ¹⁵ cm ⁻³ . This n-type GaP single crystal is cut into a predetermined thickness,
The surface is wrapped and polished to make n-type Ga
A P single crystal substrate was obtained. EP of the obtained GaP single crystal substrate
D was 1 × 10 ² cm ⁻² .

Next, a GaP yellow-green light emitting diode was manufactured using the n-type GaP single crystal substrate. FIG. 4 schematically shows the structure of the GaP yellow-green light emitting diode manufactured in this example.
Shown in In FIG. 4, 8 is an n-type GaP single crystal substrate, 9
Is an Si-doped n-type GaP epitaxial layer, 10 is an n-type GaP epitaxial layer doped with nitrogen (N), 11
Is a p-type GaP epitaxial layer.

The above-mentioned GaP yellow-green light emitting diode was manufactured by the following method. The n-type Ga grown by the LEVB method is placed in a substrate holder of a known horizontal slide boat.
An n-type GaP single crystal substrate 8 made of a P single crystal was set, and a predetermined amount of Ga metal serving as a growth solution was set in a solution reservoir. With the substrate and Ga metal separated, set this slide boat in an epitaxial growth furnace,
The temperature was raised to 1000 ° C. under a hydrogen stream, and the surface of the n-type GaP single crystal substrate 8 was brought into contact with the Ga metal by sliding the substrate holder, and held for 1 hour, so that the n-type Ga
Part of the P single crystal substrate 8 was dissolved until it was saturated. At this time, Si contained in a part of the dissolved n-type GaP single crystal substrate 8 and Si generated by reducing quartz in the reaction tube of the epitaxial growth furnace with hydrogen dissolve into the Ga metal. Then, gradually cool to 960 ° C.
An Si-doped n-type GaP epitaxial layer 9 was grown on a single crystal substrate 8. Next, while maintaining the temperature at 960 ° C., the atmospheric gas is switched from hydrogen to argon gas to which a predetermined amount of ammonia gas has been added. By doing so, the ammonia gas reacts with the Ga solution, and nitrogen (N) is taken into the Ga solution. Thereafter, the temperature is gradually cooled to 900 ° C., and N-type
A doped n-type GaP epitaxial layer 10 was grown. Subsequently, the temperature was maintained at 900 ° C., and vapor of zinc (Zn) was supplied into the atmosphere gas to incorporate a predetermined amount of Zn into the Ga solution. The temperature is gradually cooled again to 800 ° C.
A Zn-doped p-type GaP epitaxial layer 11 was grown on the doped n-type GaP epitaxial layer 10. After the growth was completed, the growth solution was separated by sliding the substrate holder and cooled to room temperature to obtain an epitaxial wafer for a GaP yellow-green light emitting diode.

Next, an Au—Be alloy is deposited on the front side of the obtained epitaxial wafer for GaP yellow-green light emitting diode, and an Au—Ge alloy is deposited on the back side. After forming electrodes by photolithography, the electrodes are cut and separated. A GaP yellow-green light emitting diode was obtained. The luminance of the obtained GaP yellow-green light emitting diode was 164 (relative value).

Comparative Example 1 First, an n-type GaP single crystal was grown by a known liquid-sealed Czochralski (LEC) method. Si was used as a dopant, and the carrier concentration was adjusted to be 2 × 10 ¹⁷ cm ⁻³ . Note that no measures were taken to prevent S from being mixed into the single crystal. The S concentration in the obtained GaP single crystal was 7 × 10 ¹⁶ c
m ^-3 . This n-type GaP single crystal is cut into a predetermined thickness, and the surface is wrapped and polished to obtain a mirror-finished n-type GaP single crystal.
A type GaP single crystal substrate was obtained. The EPD of the obtained GaP single crystal substrate was 2 × 10 ⁴ cm ⁻² . Next, this n
A GaP yellow-green light emitting diode was manufactured using the same type of GaP single crystal as in Example 1. Ga obtained
The luminance of the P yellow-green light emitting diode was 120 (relative value). Comparing Example 1 with Comparative Example 1, the luminance of Example 1 was about 37% higher.

(Embodiment 2) Next, an example of a GaP pure green light emitting diode will be described. FIG. 5 schematically shows the structure of the GaP pure green light emitting diode manufactured in this example. In FIG. 5, reference numeral 12 denotes an n-type GaP single crystal substrate, 1
3 is an n-type GaP epitaxial layer not doped with N, 1
Reference numeral 4 denotes a p-type GaP epitaxial layer.

The above-mentioned GaP pure green light emitting diode was manufactured by the following method. An n-type GaP single crystal substrate 12 having an EPD of 5 × 10 ² cm ⁻² manufactured in the same manner as in Example 1 is set in a substrate holder of a known horizontal slide boat, and a growth solution is provided in a solution reservoir. A predetermined amount of Ga metal, GaP polycrystal, and Te as an n-type dopant were set. The GaP single crystal substrate 12 has a carrier concentration of 5 × 10 ¹⁷ cm ⁻³ using Si as a dopant,
The S concentration in the GaP single crystal substrate 12 is 1 × 10 ¹⁶ c
m ^-3 . With the substrate and the growth solution separated, the slide boat was set in an epitaxial growth furnace, heated to 1000 ° C. under a hydrogen stream, held for 1 hour, and dissolved in Ga metal until GaP polycrystal was saturated. I let it. Then, slide the substrate holder to make the n-type G
The surface of the aP single crystal substrate 12 is brought into contact with the growth solution,
Slowly cooled to 00 ° C., and Te was deposited on n-type GaP single crystal substrate 12.
A doped n-type GaP epitaxial layer 13 was grown.
Subsequently, while maintaining at 900 ° C.,
After a predetermined amount of Zn was taken in the growth solution by flowing steam, the temperature was gradually cooled to 800 ° C. to grow the p-type GaP epitaxial layer 14 on the n-type GaP epitaxial layer 13. After the growth, the growth solution was separated by sliding the substrate holder and cooled to room temperature to obtain an epitaxial wafer for GaP pure green light emitting diode.

Next, an Au-Be alloy is vapor-deposited on the front side of the obtained epitaxial wafer for GaP pure green light-emitting diode, and an Au-Ge alloy is vapor-deposited on the back side. After forming electrodes by photolithography, the electrodes are cut and separated. A GaP pure green light emitting diode was obtained. The luminance of the obtained GaP pure green light emitting diode was 21.7 (relative value).

Comparative Example 2 Using the same n-type GaP single crystal substrate as produced in Comparative Example 1, a GaP pure green light emitting diode was produced in the same process as in Example 2. The luminance of the obtained GaP pure green light emitting diode was 16.2 (relative value). Comparing Example 2 with Comparative Example 2, the luminance of Example 2 was about 34% higher.

(Embodiment 3) Next, an example of a GaP red light emitting diode will be described. FIG. 6 shows the structure of the GaP red light emitting diode manufactured in this example. FIG.
, 15 is an n-type GaP single crystal substrate, 16 is an n-type G
aP epitaxial layer, 17 is p doped with Zn and O
Type GaP epitaxial layer.

The above GaP red light emitting diode was manufactured by the following method. In a known horizontal slide boat substrate holder, two EPDs produced in the same manner as in Example 1 were placed.
A × 10 ³ cm ^-2 n-type GaP single crystal substrate 15 is set, and a predetermined amount of Ga metal, GaP polycrystal, and a predetermined amount of Si as an n-type dopant are used as a solution for growing the n-type GaP epitaxial layer 16 in the solution reservoir. I set it. The GaP single crystal substrate 15 used Si as a dopant and had a carrier concentration of 8 × 10 ¹⁷ cm ⁻³ , and the S concentration in the GaP single crystal substrate 15 was 3 × 10 ¹⁶ cm ⁻³ . With the substrate and the growth solution separated, the slide boat was set in an epitaxial growth furnace, heated to 1000 ° C. under a hydrogen stream, held for 1 hour, and dissolved in Ga metal until GaP polycrystal was saturated. I let it. Thereafter, the substrate holder is slid to move the n-type GaP single crystal substrate 15.
The surface of the substrate is brought into contact with the growth solution, and gradually cooled to 800 ° C., and n-type GaP doped with Si is placed on the n-type GaP single crystal substrate 15.
An epitaxial layer 16 was grown. After the growth was completed, the growth solution was separated by sliding the substrate holder, cooled to room temperature, and then the substrate 15 on which the n-type GaP epitaxial layer 16 was grown was taken out. Next, the substrate 15 on which the n-type GaP epitaxial layer 16 has been grown is set in the substrate holder of the slide boat, and Ga metal, GaP polycrystal, which is a solution for growing the p-type GaP epitaxial layer 17, A predetermined amount of Zn and Ga ₂ O ₃ was set. This slide boat was set in an epitaxial growth furnace, and heated to 1000 ° C.
The GaP polycrystal was dissolved in the Ga metal until saturation until the metal was saturated. Thereafter, the surface of the n-type GaP epitaxial layer 16 is brought into contact with the growth solution by sliding the substrate holder, and the temperature is raised to 1005 ° C. to dissolve a part of the surface of the n-type GaP epitaxial layer 16. 95
Slowly cooling to 0 ° C., p-type GaP epitaxial layer 17 doped with Zn and O on n-type GaP epitaxial layer 16
Grew. After the growth was completed, the growth solution was separated by sliding the substrate holder and cooled to room temperature to obtain a GaP red light emitting diode epitaxial wafer. The obtained epitaxial wafer for GaP red light emitting diode was heat-treated at a predetermined temperature of about 500 ° C. for a predetermined time.

Next, an Au—Be alloy is vapor-deposited on the front side of the obtained epitaxial wafer for a GaP red light-emitting diode, and an Au—Ge alloy is vapor-deposited on the back side. A red light emitting diode was obtained. The luminance of the obtained GaP red light-emitting diode was 9.28 (relative value).

Comparative Example 3 Using the same n-type GaP single crystal substrate as that produced in Comparative Example 1, a GaP red light emitting diode was produced in the same process as in Example 3. The luminance of the obtained GaP red light emitting diode was 7.03 (relative value). Comparing Example 3 with Comparative Example 3, the luminance of Example 3 was about 32% higher.

The above Examples 1 to 3 and Comparative Example 1
In Examples 3 to 3, the case where Si was used as the dopant for the GaP single crystal substrate was described, but similar results were obtained when Te was used as the dopant.

[0031]

As described above, according to the present invention, a GaP light emitting diode having a higher luminance can be obtained as compared with the case where a conventional GaP single crystal substrate is used. In the embodiment, the case where the n-type GaP single crystal substrate manufactured by the LEVB method is used has been described. However, the method of growing the GaP single crystal is not limited to the LEVB method, and other vertical boat methods may be used. Even when a GaP single crystal is grown using
The same effect can be obtained by setting D to 3 × 10 ³ cm ⁻² or less. Further, in the embodiment, the example in which the light emitting layer is grown without growing the buffer layer on the n-type GaP single crystal substrate has been described, but the light emission is performed after growing the buffer layer on the n-type GaP single crystal substrate. Similar effects can be obtained when a layer is grown.

[Brief description of the drawings]

FIG. 1 shows GaP in a GaP yellow-green light emitting diode.
FIG. 5 is a graph showing a relationship between EPD and luminance of a single crystal substrate.

FIG. 2 shows EPD in a GaP yellow-green light emitting diode
FIG. 4 is a diagram showing the relationship between the S concentration and the luminance in a GaP single crystal substrate when a GaP single crystal substrate having a density of 3 × 10 ² cm ⁻² is used.

FIG. 3 is a schematic sectional view of an LEVB single crystal growing furnace.

FIG. 4 is a schematic diagram showing a structure of a GaP yellow-green light emitting diode according to the first embodiment.

FIG. 5 is a schematic diagram showing a structure of a GaP pure green light emitting diode according to a second embodiment.

FIG. 6 is a schematic diagram showing a structure of a GaP red light emitting diode according to a third embodiment.

[Explanation of symbols]

1 crucible 2 seed crystal 3 GaP polycrystal 4 B ₂ O ₃ 5 heater 6 crucible supporting table 7 the pressure vessel 8 n-type GaP single crystal substrate 9 Si-doped n-type GaP epitaxial layer 10 nitrogen (N) doped n-type GaP epitaxial Layer 11 p-type GaP epitaxial layer 12 n-type GaP single crystal substrate 13 n-type GaP epitaxial layer not doped with N 14 p-type GaP epitaxial layer 15 n-type GaP single crystal substrate 16 n-type GaP epitaxial layer 17 Zn and O doped p-type GaP epitaxial layer

Claims (5)

[Claims] An epitaxial wafer for a GaP light emitting diode comprising a pn junction formed by laminating at least one n-type GaP epitaxial layer and at least one p-type GaP epitaxial layer on a GaP single crystal substrate. The dislocation density (EPD) of the GaP single crystal substrate is 3 × 10 ³ cm ⁻² or less;
GaP emission wherein the dopant of the aP single crystal substrate is tellurium (Te) or silicon (Si), and the concentration of sulfur (S) in the GaP single crystal substrate is 5 × 10 ¹⁶ cm ⁻³ or less. Epitaxial wafer for diode. 2. The dislocation density of the GaP single crystal substrate is 1 ×
The epitaxial wafer for a GaP light emitting diode according to claim 1, wherein the epitaxial wafer is 10 ³ cm ^-2 or less. 3. The method according to claim 1, wherein the GaP single crystal substrate has a sulfur concentration of 2%.
3. The epitaxial wafer for a GaP light emitting diode according to claim 1, wherein the epitaxial wafer is at most 10 ¹⁶ cm ^-3 . 4. The epitaxial wafer for a GaP light emitting diode according to claim 1, wherein the GaP single crystal substrate is a substrate made of a GaP single crystal grown by a vertical boat method. 5. A GaP fabricated from the epitaxial wafer for a GaP light emitting diode according to claim 1.
Light emitting diode.