JP2008244065A - Manufacturing method of epitaxial wafer for led (light emitting diode) - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture by high yield epitaxial wafer for LED, reduced in the contents of oxygen impurities in an epitaxial layer and excellent in light emitting characteristics, by removing oxygen contained in the material of the epitaxial layer effectively to reduce the concentration of oxygen in growth solution. <P>SOLUTION: In the manufacturing method of the epitaxial wafer, having a p<SP>-</SP>type GaAlAs active layer and an n-type GaAlAs clad layer having a necessary Al mixed crystal ratio necessary for a desired light emitting wavelength, on a p-type GaAs substrate through liquid phase epitaxial method, the blending of dopant material and/or aluminum material in the preparation of growth solution is carried out by throwing the material into the growth solution under a status that the material is heated to a predetermined temperature in a growth device while the predetermined temperature T (unit:K) is specified so as to be within the range of 0.8T<SB>m</SB>≤T≤0.99T<SB>m</SB>with respect to the melting point T<SB>m</SB>(unit:K) of the material. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an epitaxial wafer manufacturing method, and more particularly to an epitaxial wafer manufacturing method suitable for a light emitting diode (LED) epitaxial wafer having a low oxygen impurity concentration.

  In recent years, light emitting diodes (LEDs) have been widely used as outdoor display panels and automobile lamps. However, in order to use them in such applications, it is required that the luminance is high enough to be visible even in daylight. . Therefore, various studies have been made to increase the luminance and the cost of the LED (improve the yield). For example, light emitting diodes having a hetero structure such as a single hetero structure, a double hetero structure, and a back reflection type double hetero structure have been developed.

  Taking a red LED as an example, an epitaxial wafer having a single heterostructure is composed of a p-type GaAs substrate and a p-type GaAlAs active layer and an n-type GaAlAs clad layer having an Al mixed crystal ratio required for a desired emission wavelength by liquid phase epitaxy. It is formed and manufactured sequentially by the method. In addition, an epitaxial wafer having a double heterostructure includes a p-type GaAlAs cladding layer, a p-type GaAlAs active layer having an Al mixed crystal ratio required for a desired emission wavelength, and an n-type GaAlAs cladding layer on a p-type GaAs substrate. It is formed and manufactured sequentially by the method.

  Here, when manufacturing an epitaxial wafer for red LED by the liquid phase epitaxy method, the raw materials are usually Ga (gallium), GaAs (gallium arsenide), Al (aluminum), Zn (zinc), Te (tellurium). A growth jig made of graphite (carbon) is used. Zn is used as a p-type dopant and Te is used as an n-type dopant.

  On the other hand, it is known that oxygen among the impurities mixed in the epitaxial wafer for LED greatly affects the light emission characteristics. When an impurity oxygen is combined with Ga, Al, Zn, Te, or the like in the growth solution to generate an oxide, crystal defects increase in the epitaxial layer, and the light emission characteristics are greatly deteriorated.

  Since the production of LED epitaxial wafers by the liquid phase epitaxy method is usually performed in a hydrogen atmosphere, conventionally, oxygen contained in growth jigs and raw materials has been reduced, and almost no oxygen impurities are contained in the epitaxial layer. It was thought. However, it has been found that oxygen is actually generated from moisture contained in the graphite growth jig and oxygen impurities are mixed into the epitaxial layer. In order to solve this problem, studies have been made to reduce the oxygen concentration in the growth solution.

  For example, the epitaxial wafer disclosed in Patent Document 1 (Japanese Patent Laid-Open No. 2001-15800) is subjected to high-temperature baking as a pretreatment for a graphite growth jig to remove moisture (including adhesion and adsorption) contained in the jig. Then, a manufacturing method for reducing oxygen impurities generated from moisture in the jig is disclosed by preventing the jig from coming into contact with the atmosphere.

JP 2001-15800 A

However, in the conventional epitaxial wafer described in Patent Document 1, there is no disclosure of a specific method for removing oxygen contained in the epitaxial layer material, and there is no guarantee that oxygen impurities caused by the material can be reduced. In particular, Al and Zn are easily oxidizable substances and easily form an oxide film or the like on the surface of the raw material. Further, since Zn and Te are substances having a melting point and density higher than those of Ga, Zn and Te are covered with liquid Ga when the temperature is raised in the growth apparatus to dissolve the raw material (Zn: melting point≈ 420 ° C., density ≈ 7.1 g / cm ³ , Te: melting point ≈ 450 ° C., density ≈ 6.2 g / cm ³ , Ga: melting point ≈ 30 ° C., density ≈ 5.9 g / cm ³ ). For this reason, even when the temperature is raised in a hydrogen atmosphere, the removal (reduction / purification) of the oxide film of the raw material tends to be incomplete, and there is a concern that the reduction of oxygen impurities is hindered.

  Therefore, an object of the present invention is to effectively remove oxygen contained in the epitaxial layer material and reduce the oxygen concentration in the growth solution, thereby reducing the number of oxygen impurities in the epitaxial layer and improving the emission characteristics of the LED. The object is to provide a method for manufacturing a wafer at a high yield (low cost).

In order to achieve the above object, the present invention sequentially forms, on a p-type GaAs substrate, a p-type GaAlAs active layer and an n-type GaAlAs clad layer having an Al mixed crystal ratio required for a desired emission wavelength by a liquid phase epitaxy method. Method for producing single heterostructure epitaxial wafer, or
A double heterostructure epitaxial structure in which a p-type GaAlAs cladding layer, a p-type GaAlAs active layer having an Al mixed crystal ratio required for a desired emission wavelength, and an n-type GaAlAs cladding layer are sequentially formed on a p-type GaAs substrate by liquid phase epitaxy. A wafer manufacturing method comprising:
A method for producing an epitaxial wafer, wherein mixing of a dopant material and / or an aluminum material in preparation of a growth solution is performed by introducing the material into a growth solution in a state where the material is heated to a predetermined temperature in a growth apparatus. provide.

In order to achieve the above object, according to the present invention, in the manufacturing method according to the present invention, the predetermined temperature T (unit: K) at which the dopant material and / or the aluminum material is added is the melting point T of the material. _m [unit: K] provides a method for producing an epitaxial wafer, which is a 0.8T _m ≦ T ≦ 0.99T _m against.

  Moreover, this invention provides the manufacturing method of the epitaxial wafer characterized by the said dopant material being Zn in the manufacturing method which concerns on said this invention, in order to achieve the said objective.

  Moreover, this invention provides the epitaxial wafer manufactured by the manufacturing method which concerns on said this invention, in order to achieve the said objective.

  According to the present invention, by effectively removing oxygen contained in the raw material of the epitaxial layer and reducing the oxygen concentration in the growth solution, an epitaxial wafer for LED having good emission characteristics with few oxygen impurities in the epitaxial layer is obtained. It can be manufactured at a high yield (low cost).

In this embodiment, an epitaxial wafer is manufactured by sequentially forming, on a p-type GaAs substrate, a p-type GaAlAs active layer and an n-type GaAlAs cladding layer having an Al mixed crystal ratio required for a desired emission wavelength by a liquid phase epitaxy method. A method of manufacturing a single hetero (SH) structure epitaxial wafer, or
Double hetero (DH) in which a p-type GaAlAs cladding layer, a p-type GaAlAs active layer having an Al mixed crystal ratio required for a desired emission wavelength, and an n-type GaAlAs cladding layer are sequentially formed on a p-type GaAs substrate by liquid phase epitaxy. A method of manufacturing an epitaxial wafer having a structure,
Mixing of the dopant material and / or the aluminum material in the preparation of the growth solution is performed by introducing the material into the growth solution in a state where the material is heated to a predetermined temperature in the growth apparatus, and the predetermined temperature T [unit: K]. but the melting point _{T m} [unit: K] of said material characterized in that it is a 0.8T _m ≦ T ≦ 0.99T _m against.

(Epitaxial wafer structure)
FIG. 1 is a schematic cross-sectional view showing an example of an SH wafer-structured GaAlAs red LED epitaxial wafer obtained as a result of the practice of the present invention. In this epitaxial wafer, a p-type GaAlAs active layer 2 and an n-type GaAlAs cladding layer 3 are formed on a p-type GaAs substrate 1. The p-type GaAlAs active layer 2 has, for example, a film thickness of 25 μm and an Al mixed crystal ratio of 0.35, and is doped with Zn as a p-type dopant. The n-type GaAlAs cladding layer 3 has, for example, a film thickness of 40 μm, an Al mixed crystal ratio of 0.60, and is doped with Te as an n-type dopant.

  FIG. 2 is a schematic cross-sectional view showing an example of a GaAlAs-based red LED epitaxial wafer having a DH structure obtained as a result of the implementation of the present invention. In this epitaxial wafer, a p-type GaAlAs cladding layer 4, a p-type GaAlAs active layer 2 ′, and an n-type GaAlAs cladding layer 3 ′ are formed on a p-type GaAs substrate 1. The p-type GaAlAs cladding layer 4 has, for example, a film thickness of 20 μm and an Al mixed crystal ratio of 0.6, and is doped with Zn as a p-type dopant. The p-type GaAlAs active layer 2 ′ has a thickness of 2 μm and an Al mixed crystal ratio of 0.35, for example, and is doped with Zn as a p-type dopant. The n-type GaAlAs cladding layer 3 ′ has, for example, a film thickness of 40 μm and an Al mixed crystal ratio of 0.6, and is doped with Te as an n-type dopant.

(Growth jig in liquid phase epitaxy method)
The growth jig in the liquid phase epitaxy method will be described by taking the case of the SH structure epitaxial wafer as shown in FIG. 1 as an example. In the case of the DH structure epitaxial wafer as shown in FIG. 2, a growth solution reservoir for the p-type cladding layer 4, a material input container, and an accompanying jig are added to FIG.

  FIG. 3 is a schematic cross-sectional view showing an example of a slide boat type growth jig and an epitaxial layer growth method in the liquid phase epitaxy method for carrying out the present invention. The growth jig main body 10 is formed of a graphite material and accommodates an active layer growth solution reservoir 12 ′, a cladding layer growth solution reservoir 13 ′, an active layer dopant material (Zn) 14, and an active layer material (Al) 16. A container 17, a container 18 that contains a cladding layer dopant material (Te) 15 and a cladding layer material (Al) 16 ′, and a substrate holder 11 that houses the substrate 1. Further, it has a push bar 19 for sliding the bottom lid 17 ′ of the container 17, a pull bar 20 for sliding the bottom lid 18 ′ of the container 18, and a pull bar 21 for sliding the substrate holder 11. ing. The growth apparatus is not shown.

(Epitaxial wafer manufacturing method)
The epitaxial wafer as shown in FIG. 1 is manufactured in the following procedure, for example. A substrate holder 11 containing the substrate 1 is set on the growth jig body 10. The active layer growth solution reservoir 12 ′ and the cladding layer growth solution reservoir 13 ′ of the growth jig body 10 contain Ga and GaAs as raw materials for the epitaxial layer, and the container 17 contains the active layer dopant material (Zn) 14 and the active layer material. The (Al) 16 is accommodated, and the cladding layer dopant material (Te) 15 and the cladding layer material (Al) 16 ′ are accommodated in the container 18. As described in Japanese Patent Application Laid-Open No. 2001-15800, it is preferable that the growth jig body 10 is preliminarily heated at a high temperature and then the jig is not exposed to the atmosphere.

  The growth jig body 10 containing the substrate and the epitaxial layer material is placed at a predetermined location in the liquid phase epitaxial growth apparatus. The push rod 19 and the pull rods 20 and 21 may be attached as appropriate. The growth jig body is heated to 850 to 950 ° C. at a rate of 1 to 5 ° C./min in a hydrogen stream. At a predetermined temperature T [unit: K] in the middle of the temperature rise, the bottom lid 17 ′ of the container 17 is slid stepwise using the push rod 19, and the active layer dopant material (Zn) 14 and the active layer material ( Al) 16 is charged into the active layer growth solution 12 in the active layer growth solution reservoir 12 '. Similarly, at a predetermined temperature T [unit: K], the bottom lid 18 ′ of the container 18 is slid stepwise using the pull rod 20, and the cladding layer dopant material (Te) 15 and the cladding layer material (Al). 16 'is thrown into the cladding layer growth solution 13 in the cladding layer growth solution reservoir 13'. Since the melting point of Al (about 660 ° C.) is higher than the melting point of Zn (about 420 ° C.) and the melting point of Te (about 450 ° C.), it is desirable to slide the bottom lids 17 ′ and 18 ′ stepwise.

At this time, the predetermined temperature T [Unit: K] is the melting point _{T m} [unit: K] of the material to be introduced is preferably a 0.8T _m ≦ T ≦ 0.99T _m against. More preferably a 0.9T _m ≦ T ≦ 0.99T _m, more desirably 0.95T _m ≦ T ≦ 0.98T _m. When the predetermined temperature T is T <0.8 _Tm , reduction / purification (removal of the oxide film) of the input material tends to be incomplete, resulting in a decrease in yield. In addition, when the predetermined temperature T is 0.99 T _m <T, the material to be melted is incompletely charged due to the melting point drop due to the degree of supercooling (for example, due to the curvature radius of the material surface). Therefore, the composition of the growth solution is likely to be misaligned, resulting in deterioration of the light emission characteristics.

Note that it is preferable to provide a holding time at a predetermined temperature T. In addition, since the Al material has a density (about 2.7 g / cm ³ ) smaller than the Ga density (about 5.9 g / cm ³ ) and floats in liquid Ga, the material is reduced and purified even after the growth solution is added. Therefore, it is possible to simultaneously add with a dopant material such as Zn or Te. It is also possible to store in the active layer growth solution reservoir 12 ′ and the clad layer growth solution reservoir 13 ′ in advance.

  After heating up to 850-950 degreeC mentioned above, it hold | maintains for 2 to 5 hours, and stabilizes a growth solution. Thereafter, while lowering the temperature to 700 ° C. at a rate of 0.5 to 2 ° C./min, the substrate holder 11 is slid using the pulling rod 21, the substrate 1 is sequentially brought into contact with the growth solutions 12 and 13, and p-type GaAlAs is obtained. An active layer and an n-type GaAlAs cladding layer are epitaxially grown. Thereby, an epitaxial wafer is manufactured.

(Other growth jigs)
FIG. 4 is a schematic cross-sectional view showing another example of a slide boat type growth jig and an epitaxial layer growth method in the liquid phase epitaxy method for carrying out the present invention. The growth jig body 30 is formed of a graphite material, and includes an active layer growth solution reservoir 32, a clad layer growth solution reservoir 33, a container 34 containing an active layer dopant material (Zn) 14, and an active layer material (Al). 16, a container 35 for storing the cladding layer dopant material (Te) 15, a container 37 for storing the cladding layer material (Al) 16 ′, and a substrate holder 31 for storing the substrate 1. Yes. In addition, a rotating rod 39 for rotating the container 34, a rotating rod 39 'for rotating the container 36, a rotating rod 40 for rotating the container 35, and a rotating rod 40' for rotating the container 37. And a pulling rod 41 for sliding the substrate holder 31. Note that the growth apparatus is not shown.

  The production of the epitaxial wafer using the growth jig of FIG. 4 is performed in the same manner as in the case of using the growth jig of FIG. In addition, when the active layer dopant material (Zn) 14, the active layer material (Al) 16, the clad layer dopant material (Te) 15, and the clad layer material (Al) 16 'are added to each growth solution, the growth treatment shown in FIG. Instead of “sliding the bottom lids 17 ′ and 18 ′ stepwise” in the case of using tools, the containers 34 to 37 are sequentially rotated from the lower input temperature T by using the turning rods 39 to 40 ′. Done.

[Effect of the embodiment]
According to the above embodiment of the present invention, the following effects can be obtained.
(1) In the preparation of the growth solution, the oxygen component contained in the dopant material and the aluminum material can be effectively removed, so that the oxygen concentration in the growth solution can be reduced.
(2) Since the reduction of the oxygen concentration in the growth solution leads to the reduction of oxygen impurities in the epitaxial layer, it is possible to produce an LED epitaxial wafer with good light emission characteristics at a high yield (low cost).

  EXAMPLES Hereinafter, although this invention is demonstrated in more detail based on an Example, this invention is not limited to these.

(Production of Examples 1 to 3 and Comparative Examples 1 to 4)
First, a graphite slide boat type growth jig as shown in FIG. 3 was prepared as a growth jig. This growth jig is baked (held in a hydrogen atmosphere at 950 ° C. for 10 hours) to remove moisture contained in the jig, and then a glove in a nitrogen atmosphere is used so that the jig does not come into contact with the atmosphere. Stored in a box.

  Next, Ga, GaAs, Al, Zn, and Te, which are raw materials for the p-type GaAs substrate and the epitaxial layer, were set in a growth jig in the glove box. At this time, as in the prior art, Comparative Example 1 was prepared by containing Ga, GaAs, Al, and Zn in the active layer growth solution reservoir and containing Ga, GaAs, Al, and Te in the cladding layer growth solution reservoir. On the other hand, in other comparative examples (Comparative Examples 2 to 4) and Examples 1 to 3, the dopant raw material (Zn, Te) and the Al raw material are respectively shown in FIG. It was stored in a container different from the solution reservoir. Thereafter, each growth jig was placed at a predetermined location in the liquid phase epitaxial growth apparatus while not touching the atmosphere.

  Next, the growth apparatus was heated to 900 ° C. at a rate of 3 ° C./min in a hydrogen stream. The dopant raw materials (Zn, Te) and the Al raw material were added to the active layer growth solution and the clad layer growth solution at a predetermined temperature during the temperature increase. At this time, the input temperature of the active layer dopant raw material (Zn) was changed, and charged at 200 ° C. (Comparative Example 2), charged at 250 ° C. (Comparative Example 3), charged at 300 ° C. (Example 1), and at 350 ° C. Input (Example 2), input at 400 ° C. (Example 3), and input at 450 ° C. (Comparative Example 4). Further, the input temperatures of the cladding layer dopant raw material (Te) and the Al raw material were unified at 400 ° C. and 600 ° C. through Comparative Examples 2 to 4 and Examples 1 to 3, respectively.

  After reaching 900 ° C., the growth solution was stabilized by maintaining for 3 hours. Next, the p-type GaAs substrate is sequentially brought into contact with the growth solution while the temperature is decreased to 700 ° C. at a rate of 1 ° C./min, and the p-type GaAlAs active layer and the n-type GaAlAs cladding layer are epitaxially grown. An epitaxial wafer for LED was produced.

(Emission characteristic evaluation)
The light emission characteristics of each epitaxial wafer produced above were evaluated. First, using a grooving measuring device (manufactured by Opt-System Co., Ltd., model: WG-105), a ring-shaped groove (outside diameter φ0.9 mm, inside diameter φ0.6 mm, pn interface depth or more) on the epitaxial wafer surface ). Next, the electrode needle was brought into contact with the upper surface of the island part (outer diameter φ0.6 mm) at the center of the groove processing, and the light emission characteristics were measured by applying current between the wafer back electrode (separately formed). The energizing current was 20 mA, and 1000 locations were measured under each production condition (Examples 1 to 3 and Comparative Examples 1 to 4). Those having a light emission characteristic of less than 10 mcd were determined to be defective, and the defect occurrence rate was determined. The results are shown in Table 1.

As is clear from the results in Table 1, the predetermined temperature T [unit: K] for introducing the dopant material and the aluminum material is 0.8 T _m ≦ T ≦ with respect to the melting point T _m [unit: K] of the material. It can be seen that the LEDs (Examples 1 to 3) using the epitaxial wafer of 0.99 _Tm exhibited a low defect occurrence rate and could be manufactured with a high yield. This is because the oxygen component contained in the dopant material and the aluminum material can be effectively removed (reduction / purification) in the temperature rising process of the growth apparatus, so that the oxygen concentration in the growth solution can be reduced. As a result, it is considered that oxygen impurities in the epitaxial layer are reduced.

  On the other hand, it can be seen that the defect occurrence rate is hardly improved in the epitaxial wafers for LEDs (Comparative Examples 1 to 4) manufactured outside the definition of the present invention. This is presumably because the removal (reduction / purification) of the oxygen component contained in the dopant material and the aluminum material was insufficient.

  In Comparative Example 4, the dopant material (Zn) input temperature exceeds the melting point of Zn, and the amount of dopant input accompanying the melting of Zn in the container (in other words, outside the active layer growth solution reservoir). It is thought that the shortage occurred and the defect occurrence rate increased.

  Although the above embodiment is performed on an epitaxial wafer having a single hetero structure, the same effect can be expected also on an epitaxial wafer having a double hetero structure. The present invention can also be applied to a back-reflection type light emitting diode manufactured by removing a GaAs substrate from an epitaxial wafer having a double hetero structure.

It is a cross-sectional schematic diagram which shows an example of the epitaxial wafer for GaAlAs type | system | group red LED of SH structure obtained as a result of implementation of this invention. It is a cross-sectional schematic diagram which shows an example of the epitaxial wafer for GaAlAs type | system | group red LED of DH structure obtained as a result of implementation of this invention. It is the cross-sectional schematic diagram which showed one example of the slide boat type growth jig | tool and the epitaxial layer growth method in the liquid phase epitaxy method for implementing this invention. It is the cross-sectional schematic diagram which showed another example of the slide boat type growth jig | tool and the epitaxial layer growth method in the liquid phase epitaxy method for implementing this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Board | substrate, 2, 2 '... Active layer, 3, 3' ... Cladding layer, 4 ... Cladding layer, 10 ... Growth jig main body, 11 ... Substrate holder, 12 ... Active layer growth solution, 12 '... Active layer growth Solution reservoir, 13 ... cladding layer growth solution, 13 '... cladding layer growth solution reservoir, 14 ... active layer dopant material, 15 ... cladding layer dopant material, 16 ... active layer material, 16' ... cladding layer material, 17, 18 ... Container, 17 ', 18' ... Bottom lid, 19 ... Push rod, 20, 21 ... Pull rod, 30 ... Growth jig body, 31 ... Substrate holder, 32 ... Active layer growth solution reservoir, 33 ... Clad layer growth solution reservoir , 34, 35, 36, 37 ... container, 39, 39 ', 40, 40' ... rotating rod, 41 ... pulling rod.

Claims (4)

A method for producing a single heterostructure epitaxial wafer in which a p-type GaAlAs active layer and an n-type GaAlAs cladding layer having an Al mixed crystal ratio necessary for a desired emission wavelength are sequentially formed on a p-type GaAs substrate by liquid phase epitaxy, or
A double heterostructure epitaxial structure in which a p-type GaAlAs cladding layer, a p-type GaAlAs active layer having an Al mixed crystal ratio required for a desired emission wavelength, and an n-type GaAlAs cladding layer are sequentially formed on a p-type GaAs substrate by liquid phase epitaxy. A wafer manufacturing method comprising:
A method for producing an epitaxial wafer, wherein mixing of a dopant material and / or an aluminum material in preparation of a growth solution is performed by introducing the material into a growth solution in a state where the material is heated to a predetermined temperature in a growth apparatus. 2. The manufacturing method according to claim 1, wherein the predetermined temperature T [unit: K] at which the dopant material and / or the aluminum material is charged is 0.8 T _{m with} respect to the melting point T _m [unit: K] of the material. method for manufacturing an epitaxial wafer, which is a ≦ T ≦ 0.99T _m.   3. The method for manufacturing an epitaxial wafer according to claim 1, wherein the dopant material is Zn. 4.   An epitaxial wafer manufactured by the manufacturing method according to claim 1.

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