JPH11346000A - Epitaxial wafer, its manufacture, and light emitting diode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture an epitaxial wafer for a light emitting diode which does not exhibit thyristor characteristics, i.e., does not form a P-N-P-N interface in the vicinity of a composition interface, with yield higher than the conventional yield. SOLUTION: In an epitaxial wafer of P-type GaAlAs based single hetero structure or double hetero structure, the concentration of carbon in an N-type GaAlAs clad layer 3 is made at most 1×10<17> cm<-3> . Thereby the concentration of carbon in the vicinity of a composition interface which is contained as impurities in the N-type GaAlAs clad layer 3 in the course of manufacture is made lower than the concentration of N-type dopant Te to be contained in the N-type GaAlAs clad layer 3. The concentration of the N-type dopant Te is 1×10<17> cm<-3> . A graphite jig subjected to PBN coating is used in the course of manufacture.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an epitaxial wafer, a method for manufacturing the same, and a light-emitting diode, and more particularly to a device having an improved pn junction.

[0002]

2. Description of the Related Art In recent years, the luminance of red light-emitting diodes using GaAlAs has been improved, and they have been used as display panels and high-mount stop lamps for automobiles. For use in these applications, it is required that the luminance be high enough to be visible even in daylight. In order to meet this demand, a single heterostructure (SH
Structure), double hetero structure (DH structure), back reflection type D
Light emitting diodes (LEDs) having a heterostructure such as an H structure have been developed.

As shown in FIG. 4, an epitaxial wafer having a single hetero structure is formed on a p-type GaAs substrate 21 by
P-type GaAlA with Al mixed crystal ratio required for desired emission wavelength
An s active layer 22 and an n-type GaAlAs cladding layer 23 are sequentially formed by a liquid phase epitaxial method. An epitaxial wafer having a double hetero structure is not shown, but is formed on a p-type GaAs substrate by p-type GaAlAs.
Cladding layer, p of Al mixed crystal ratio required for desired emission wavelength
A GaAlAs active layer and an n-type GaAlAs cladding layer are sequentially formed by a liquid phase epitaxial method.

[0004] Usually, when producing an epitaxial wafer for a red light emitting diode by a liquid phase epitaxial method,
Zn is used as a p-type dopant. Zn has a property of being very easily diffused at a temperature at which epitaxial growth is performed (900 to 700 ° C.).

[0005] Therefore, in the case of an ordinary single-heterostructure epitaxial wafer shown in FIG. 4, Zn in the p-type active layer 22 diffuses into the n-type cladding layer 23, and as shown in FIG. The composition interface formed between the active layer 22 and the n-type cladding layer 23 and the pn interface have a.
A shift of 5 to 1.5 μm occurs. If the deviation is large, there is a problem that the luminance is reduced.

In addition, the pn interface becomes a pnpn interface, which causes a parasitic effect that the light emitting diode exhibits thyristor characteristics. This is also caused by Zn diffusion. As shown in FIG. 5, when the Te diffusion amount (curve 24) used as the n-type dopant partially falls below the Zn diffusion amount (curve 25) used as the p-type dopant, pnpn-n There is a problem that the interface becomes an interface and the occurrence rate of thyristor characteristics increases.

Therefore, there is a demand for a technique for producing an epitaxial wafer which does not exhibit thyristor characteristics with high luminance by preventing the diffusion of Zn into the n-type cladding layer 23. In order to prevent the displacement between the composition interface and the pn interface from occurring, studies have been made to increase the amount of dopant Te diffused in the n-type cladding layer 23 and to reduce the amount of Zn in the p-type active layer 22.

[0008]

However, the amount of Te diffusion in the n-type cladding layer is increased or the Zn diffusion in the p-type active layer is increased.
Reducing the amount creates new problems, such as:

(1) When the Te diffusion amount is increased, the crystallinity of the n-type cladding layer is deteriorated, so that the luminance is reduced.

(2) On the other hand, when the amount of Zn is reduced, the carrier concentration range of 0.5 to 15 × 10 ¹⁷ cm ⁻³ , which is optimal from the viewpoint of luminance, cannot be secured. Decrease.

(3) The thyristor characteristic caused by the diffusion of Zn cannot be solved for the same reason as in the above (1) and (2).

This problem arises not only in a single-heterostructure epitaxial wafer but also in a double-heterostructure epitaxial wafer, and also in a back-reflection type light-emitting diode made by removing a GaAs substrate from a double-heterostructure epitaxial wafer. Occurs similarly.

Therefore, a structure that does not become a pnpn interface near the composition interface by a method other than increasing the Te diffusion amount of the n-type cladding layer or decreasing the Zn amount of the p-type active layer. It is desired to provide a technique for manufacturing a light emitting diode with a high yield. This demand is not limited to GaAlAs-based red LEDs, but is also common to GaAlAs-based infrared LEDs and optical semiconductor elements including light-receiving elements.

Therefore, an object of the present invention is to solve the above-mentioned problem and to manufacture a light emitting diode which does not exhibit thyristor characteristics, ie, does not become a pnpn interface near a composition interface, with a higher yield than before. An object of the present invention is to provide an epitaxial wafer, a method of manufacturing the same, and a light emitting diode.

[0015]

Means for Solving the Problems In order to achieve the above object, the present invention is configured as follows.

(1) The epitaxial wafer of the present invention comprises:
A p-type active layer composed of a III-V compound semiconductor doped with a p-type dopant and an n-type dopant doped with an n-type dopant
In an epitaxial wafer formed by a liquid phase epitaxy method using an n-type cladding layer composed of a III-V compound semiconductor as a heterojunction, the concentration near the composition interface of carbon (C) contained as an impurity in the n-type cladding layer is determined by: The structure is such that the concentration of the n-type dopant contained in the n-type cladding layer is lower than 1 × 10 ¹⁷ cm ⁻³ (claim 1).

The epitaxial wafer having a heterojunction assumed here includes a GaAlAs red LED and a GaP red LE as constituents of a semiconductor optical device.
D, a light-emitting element such as a GaAlAs infrared LED or a light-receiving element such as an InGaAs photodiode is also included. In particular, as a GaAlAs-based red LED, an DH structure LE formed on a p-type GaAs substrate is used.
There are LEDs having D and SH structures, and LEDs having a back reflection type DH structure from which a substrate is removed, and any epitaxial wafer used for these is included in the present epitaxial wafer.

More specifically, on a p-type GaAs substrate,
A p-type GaAlAs active layer doped with a p-type dopant and having an Al mixed crystal ratio required for a desired emission wavelength and an n-type GaAlAs clad layer doped with an n-type dopant are sequentially formed by a liquid phase epitaxial method. It may be in the form of an epitaxial wafer having a hetero structure (SH structure), or may be formed on a p-type GaAs substrate by p-type G
aAlAs lower cladding layer, a p-type GaAlAs active layer doped with a p-type dopant and having an Al mixed crystal ratio required for a desired emission wavelength, and an n-type GaAlAs upper cladding layer doped with an n-type dopant in a liquid phase. Double hetero structure (DH structure) formed sequentially by epitaxial method
In the form of an epitaxial wafer. In any of the SH structure and the DH structure, the n-type Ga
The concentration of the carbon contained in the AlAs upper cladding layer in the vicinity of the composition interface can be reduced to 1 × 10 ¹⁷ cm ⁻³ or less (claims 2 and 3).

The p-type dopant can be Zn or Mg (claim 4), and the n-type dopant is T
e can be used (claim 5). Where Mg is p
It is disclosed in Japanese Patent Application Laid-Open No. 5-235409 that the p-type dopant can be used optimally for improving the n-interface, and the present invention can be applied similarly to the case of general Zn.

(2) The method for producing an epitaxial wafer according to the present invention is the method for producing an epitaxial wafer according to the first, second, third, fourth or fifth aspect by the liquid phase epitaxial method. The tool uses a graphite jig coated with PBN (Pyrolitic Boron Nitride: pyrolytic boron nitride).

(3) A light emitting diode according to the present invention is a light emitting diode manufactured by using the epitaxial wafer according to claim 1, 2, 3, 4 or 5 (claim 7), or the epitaxial wafer according to claim 6. (Embodiment 8).

The basis of the present invention is as follows. That is, the present inventors have conducted intensive studies based on many years of measures against thyristor failure, and as a result, have found that p-n-p near the composition interface.
It has been found that the cause of the −n interface is not only the diffusion of Zn into the n-type cladding layer but also the impurity C (carbon) contained in the n-type cladding layer.

FIG. 3 shows that p-type GaAs is formed on a p-type GaAs substrate.
6 shows SIMS measurement results of the C concentration near the composition interface in the SH structure epitaxial wafer in which the lAs active layer and the n-type GaAlAs cladding layer are liquid phase epitaxially grown. Since the growth jig used for liquid phase epitaxial growth is made of graphite, C is naturally contained in the solution and therefore also in the epitaxial layer, but the peak concentration is as shown in FIG. High concentration of 1 × 10 ¹⁷ cm ⁻³ or more near the composition interface. Usually, the Te concentration near the composition interface of the n-type cladding layer is 1 to 5 × 10 ^17.
Since it is cm ^-3 , if C, which is a p-type impurity, is further contained, the n-type cladding layer is converted to p-type.

Therefore, the impurity C concentration in the n-type cladding layer must not be higher than the Te concentration in the n-type cladding layer. That is, the Te concentration in the vicinity of the composition interface of the n-type cladding layer must be 1 to 5 × 10 ¹⁷ cm ⁻³ or less.

Although the above description has been made with reference to an example of an epitaxial wafer having a single hetero structure, the same applies to an epitaxial wafer having a double hetero structure.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on the illustrated embodiment.

(Embodiment 1) FIG. 1 shows the structure of an epitaxial wafer for a GaAlAs-based SH structure red LED as a first embodiment. This epitaxial wafer is composed of a p-type GaAs substrate 1 on which a p-type GaAlAs active layer 2 and an n-type GaAlAs cladding layer 3 are sequentially grown by a liquid phase epitaxial method.

The p-type GaAlAs active layer 2 has a thickness of 25 μm.
m, Al mixed crystal ratio is 0.35, and Zn is doped as a p-type dopant. The carrier concentration of the active layer of the LED is
Generally, the amount is in the range of 1 × 10 ¹⁷ cm ⁻³ to 1 × 10 ¹⁹ cm ⁻³ , and therefore, the doping amount of Zn is set in this range.

The n-type GaAlAs cladding layer 3 has a thickness of 4
0 μm, Al mixed crystal ratio 0.60, T as n-type dopant
e is doped, and the Te concentration near the composition interface of the n-type cladding layer is 3 × 10 ¹⁷ cm ⁻³ . Also, n-type GaAl
Generally, the concentration of carbon (C) contained in the As cladding layer 3 during the manufacturing process is 1 × 1
Although the concentration is as high as 0 ¹⁷ cm ⁻³ or more, the peak concentration of carbon (C) is 1 × 10 ¹⁷ cm ⁻³ or less in the epitaxial wafer of FIG.

Next, a method of manufacturing the epitaxial wafer for a GaAlAs-based red LED having the SH structure and an embodiment of a light emitting diode obtained therefrom will be described.

First, PBN (Pyrolitic) is used as a growth jig.
Prepare a graphite jig with Boron Nitride (pyrolytic boron nitride) coating.

Ga, GaAs, Al, which are the raw materials of the p-type GaAs substrate 1 and the epitaxial layer formed thereon,
Zn and Te were set in a growth jig and set at predetermined locations in a liquid phase epitaxial growth apparatus. The growth apparatus was heated to 900 ° C. in a hydrogen stream, and maintained at 700 ° C. for 3 hours.
The temperature was lowered at a rate of 1 ° C./min. The substrate was sequentially brought into contact with a growth solution during cooling, and a p-type GaAlAs active layer 2 and an n-type GaAlAs cladding layer 3 were successively subjected to liquid phase epitaxial growth. The Te concentration near the composition interface of the n-type GaAlAs cladding layer 3 was grown under conditions so as to be 3 × 10 ¹⁷ cm ⁻³ .

Using the half surface of the obtained epitaxial wafer, a C concentration SIMS measurement near the composition interface was performed. On the other half, after forming electrodes and forming a chip, the chip was attached to a stem and coated with an epoxy resin to prepare a light emitting diode.

As a comparative example, an epitaxial wafer was prepared under the same conditions as above using a commonly used graphite jig without PBN coating, and the C concentration SIMS measurement was performed using the half surface in the same manner as above. A light emitting diode was fabricated on the other half.

[0035]

[Table 1]

Table 1 shows the thyristor defect occurrence rate and the peak C concentration of the n-type cladding layer of this embodiment and the comparative example.

The C concentration in the vicinity of the composition interface of the n-type GaAlAs cladding layer 3 in this embodiment is 0.8 × 10 ¹⁷ cm ^−3.
And the Te concentration near the composition interface of the n-type GaAlAs cladding layer 3 was lower than 3 × 10 ¹⁷ cm ⁻³ . When a light emitting diode was actually manufactured using this epitaxial wafer, the incidence of thyristor failure was very low at 0.1%. On the other hand, in the case of the light emitting diode manufactured using the conventional epitaxial wafer of the comparative example, the occurrence rate of the thyristor defect was 30.0%.

As is apparent from the above, when a light emitting diode is manufactured using the epitaxial wafer of this embodiment,
The thyristor defect occurrence rate is reduced to 1/300 as compared with a light emitting diode using a conventional epitaxial wafer. This is because the peak C concentration is lower than the Te concentration near the composition interface of the n-type cladding layer, so that pn
This is because the -pn interface no longer occurs. For this reason,
According to the present epitaxial wafer, the T of the n-type cladding layer
GaAs that does not exhibit thyristor characteristics, ie, does not become a pnpn interface near a composition interface, without performing an operation of increasing the amount of diffusion of e or reducing the amount of Zn in the p-type active layer.
An lAs red LED can be manufactured with a higher yield than before.

(Embodiment 2) FIG. 2 shows, as a second embodiment, the structure of an epitaxial wafer for a GaAlAs-based DH structure red LED. This epitaxial wafer comprises a p-type GaAs substrate 1, a p-type GaAlAs lower cladding layer 11, a p-type GaAlAs active layer 12, an n-type Ga
The AlAs upper cladding layer 13 is formed by sequentially growing a liquid phase epitaxial method.

The p-type GaAlAs lower cladding layer 11
It has a thickness of 30 μm, an AlAs mixed crystal ratio of 0.65, and is doped with Mg as a p-type dopant.

The p-type GaAlAs active layer 12 has a thickness of 1 μm.
m, AlAs mixed crystal ratio 0.35, p-type dopant M
g is doped. In the Mg-doped liquid phase epitaxial wafer, the relationship between the amount of Mg added to the solvent used for growth and the carrier concentration varies depending on the growth temperature, but the carrier concentration in the active layer of the LED is generally 1 × 10 ¹⁷ cm ⁻ Since it is in the range of ³ to 1 × 10 ¹⁹ cm ⁻³ , the doping amount of Mg is set in this range.

The n-type GaAlAs upper cladding layer 13
A film thickness of 40 μm, an AlAs mixed crystal ratio of 0.65, Te doped as an n-type dopant, and the n-type upper cladding layer 1
The Te concentration near the composition interface of No. 3 is 3 × 10 ¹⁷ cm ⁻³ .
The concentration of carbon (C) contained in the n-type GaAlAs upper cladding layer 13 during the manufacturing process is generally as high as 1 × 10 ¹⁷ cm ⁻³ or more near the composition interface. However, in the epitaxial wafer shown in FIG. 1, the peak concentration of carbon (C) is lower than that of 1 ×
It is 10 ¹⁷ cm ^-3 or less.

Such a GaAlAs-based DH structure red LED
The epitaxial wafer for use can be easily manufactured by using a graphite jig coated with PBN similarly to the first embodiment. Further, it was confirmed that a GaAlAs-based red LED exhibiting no thyristor characteristics can be manufactured with a high yield by using this epitaxial wafer.

In the above embodiment, the epitaxial wafer having the single hetero structure and the double hetero structure has been described.
The present invention can also be applied to a back-reflection type light emitting diode made by removing the aAs substrate.

[0045]

As described above, according to the present invention, the following excellent effects can be obtained.

(1) According to the epitaxial wafer of the first to fifth aspects, the concentration near the composition interface of carbon contained as a p-type impurity in the n-type cladding layer in the manufacturing process is reduced by the n-type cladding. Since the concentration of the n-type dopant contained in the layer is lower than 1 × 10 ¹⁷ cm ⁻³ , a pnpn interface does not occur near the composition interface, and an epitaxial wafer that does not exhibit thyristor characteristics is obtained. It can be obtained without increasing the Te diffusion amount of the n-type cladding layer or reducing the Zn amount of the p-type active layer.

(2) According to the second to fifth aspects of the present invention, among such epitaxial wafers,
An aAlAs-based single-heterostructure epitaxial wafer or a GaAlAs-based double-heterostructure epitaxial wafer can be obtained.

(3) According to the method of manufacturing an epitaxial wafer according to the sixth aspect, a graphite jig coated with a PBN is used as a growth jig by a liquid phase epitaxial method. 3, 4, or 5
The described epitaxial wafer can be manufactured.
That is, the concentration near the composition interface of carbon contained as a p-type impurity in the n-type cladding layer is the concentration of the n-type dopant of 1
Since it is lower than × 10 ¹⁷ cm ⁻³ , an epitaxial wafer for a light emitting diode that does not exhibit thyristor characteristics can be manufactured with a higher yield than before.

(4) The light emitting diode according to the seventh and eighth aspects uses the epitaxial wafer according to the first, second, third, fourth or fifth aspect or uses the method for manufacturing an epitaxial wafer according to the sixth aspect. Since the light emitting diode is manufactured by using the method described above, it can be manufactured with a high yield.

[Brief description of the drawings]

FIG. 1 is a sectional view of an epitaxial wafer having a single hetero structure according to the present invention.

FIG. 2 is a sectional view of an epitaxial wafer having a double hetero structure according to the present invention.

FIG. 3 is a diagram showing a C concentration SiMS measurement result near a composition interface in a GaAlAs-based single heterostructure epitaxial wafer.

FIG. 4 is a cross-sectional view of a conventional single-hetero structure epitaxial wafer.

FIG. 5 is a view showing a conventional concentration distribution (image) of Zn and Te near a composition interface.

[Explanation of symbols]

 Reference Signs List 1 p-type GaAs substrate 2 p-type GaAlAs active layer 3 n-type GaAlAs cladding layer 11 p-type GaAlAs lower cladding layer 12 p-type GaAlAs active layer 13 n-type GaAlAs upper cladding layer 24 Zn concentration distribution curve 25 Te concentration distribution Curve showing

Claims (8)

[Claims] The liquid phase is formed by using a p-type active layer composed of a III-V compound semiconductor doped with a p-type dopant and an n-type cladding layer composed of a III-V compound semiconductor doped with an n-type dopant as a heterojunction. An epitaxial wafer formed by an epitaxial method, wherein a carbon concentration near a composition interface of the n-type cladding layer is lower than an n-type dopant concentration near a composition interface of the n-type cladding layer. 2. A p-type GaAlAs active layer doped with a p-type dopant and having an Al mixed crystal ratio required for a desired emission wavelength and an n-type GaAlAs clad doped with an n-type dopant on a p-type GaAs substrate. An epitaxial wafer having a single hetero structure in which layers are sequentially formed by a liquid phase epitaxial method, wherein the carbon concentration near the composition interface of the n-type GaAlAs cladding layer is 1 × 10 ¹⁷ cm ⁻³ or less. . 3. A p-type GaAs substrate on which a p-type GaAlAs
A lower cladding layer and a p-type GaAlA doped with a p-type dopant having an Al composition ratio required for a desired emission wavelength.
s active layer and n-type GaAs doped with n-type dopant
In an epitaxial wafer having a double hetero structure in which an lAs upper cladding layer is sequentially formed by a liquid phase epitaxial method, the carbon concentration near the composition interface of the n-type GaAlAs upper cladding layer is set to 1 × 10 ¹⁷ cm ⁻³ or less. Epitaxial wafer. 4. The epitaxial wafer according to claim 1, wherein said p-type dopant is Zn or Mg. 5. The epitaxial wafer according to claim 1, wherein said n-type dopant is Te. 6. A method of manufacturing an epitaxial wafer according to claim 1, 2, 3, 4 or 5, wherein a graphite jig having a PBN coating applied to a growth jig by the liquid phase epitaxial method. A method for producing an epitaxial wafer, characterized in that it is used. 7. A light-emitting diode manufactured using the epitaxial wafer according to claim 1, 2, 3, 4, or 5. 8. A light-emitting diode manufactured by using the method for manufacturing an epitaxial wafer according to claim 6.