Method for preparing gallium nitride phosphor

Details Method for preparing gallium nitride phosphor Method for preparing gallium nitride phosphor

1999-12-27

2001-10-16

Smith, Matthew (Department: 2825)

Semiconductor device manufacturing: process

Making device or circuit emissive of nonelectrical signal

Including integrally formed optical element

C438S505000, C438S935000, C252S301160, C252S301320, C252S30140P

Reexamination Certificate

active

06303403

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a method for preparing a gallium nitride phosphor, and more particularly to a method for preparing a Ga
1−x
In
x
N:A,B (0≦x<1, A=Zn,Mg, B=Si,Ge) phosphor.
In recent years, it has been known that gallium nitride (hereinafter generally referred also to as “GaN”) emits blue and green light at high luminance when it is incorporated in the form of a single crystal in a luminescent device such as an LED, an LD or the like. Also, it emits light in a wide luminous color range extending from a blue luminous color to a red luminous color when it is represented by a general formula Ga
1−x
In
x
N:A,B (0≦x<1, A=Zn,Mg, B=Si,Ge)
Preparation of a GaN phosphor which has been conventionally known in the art is carried out by blending a Ga compound acting as a starting material with a compound for a dopant (dopant compound) to prepare a blend and then placing the blend in a calcination oven to subject it to calcination at a high temperature while exposing it to ammonia flowed in the oven, to thereby nitride Ga and dope it with the dopant.
In the past, it has been attempted to carry out luminescence of the thus-prepared GaN phosphor by means of electron beams. However, the prior art fails to permit the phosphor to emit light at increased luminance when it is in the form of a powder.
The major reason why the phosphor fails to exhibit increased luminance is that nitriding of the GaN phosphor is hard, unlike other phosphors. More particularly, the GaN phosphor causes a difference between a temperature at which it is nitrided (700 to 1000° C.) and a temperature at which it starts to be composed (950° C.) to be reduced, so that normal heating of the phosphor for reaction thereof tends to cause nitriding and decomposition of the phosphor to concurrently progress. Thus, although the reaction leads to formation of GaN, the GaN obtained fails to exhibit crystallizability sufficient to permit it to satisfactorily act as a phosphor intended.
Also, the GaN phosphor exhibits pair-luminescence by a combination of a donor increased in valence by one as compared with Ga and an acceptor decreased in valence by one as compared with Ga, so that it is required to dope GaN with a dopant for each of the donor and acceptor. Doping of the dopant requires a significantly increased temperature. However, GaN tends to be decomposed at such a high temperature, resulting in failing in an increase in temperature, leading to a failure in satisfactory doping.
Further, preparation of a nitride such as GaN is generally carried out by subjecting a starting material or Ga compound to calcination at a high temperature in an atmosphere using ammonia, during which hydrogen produced by decomposition of ammonia exhibits a reducing action to a high degree. The reducing action causes GaN to be reduced, resulting in Ga being liberated from GaN, leading to blackening of the phosphor. Such blackening of the phosphor gives rise to a fatal disadvantage because it causes the phosphor to absorb its own luminescence, resulting in the phosphor being reduced in luminance. Also, the reducing action causes decomposition and scattering of the dopant incorporated in the GaN, leading to a failure in satisfactory diffusion of the dopant. In order to eliminate such disadvantages due to the reducing action of hydrogen, it is required to carry out the reaction at a low temperature. However, this fails to dope GaN with the dopant. Thus, the prior art fails to provide a GaN phosphor which is capable of emitting light at increased luminance.
SUMMARY OF THE INVENTION
The present invention has been made in view of the foregoing disadvantage of the prior art.
Accordingly, it is an object of the present invention to provide a method for preparing a gallium nitride phosphor which is capable of emitting light at luminance increased to a degree sufficient to permit the phosphor to be practically used.
It is another object of the present invention to provide a gallium nitride phosphor which is capable of being prevented from being blackened due to calcination at a temperature increased to a level sufficient to improve crystallizability of the phosphor.
In accordance with the present invention, a method for preparing a gallium nitride phosphor represented by a formula Ga
1−x
In
x
N:A,B (0≦x<1, A=Zn,Mg, B=Si,Ge) is provided. The method includes the step of reacting S or O with hydrogen of ammonia gas flowed from an upstream side to a downstream side in a calcination oven in which a compound constituting the phosphor is placed. The S or O is generated upstream of the compound. The method also includes the step of subjecting the compound to calcination in an atmosphere containing nitrogen and S or O to nitride gallium and dope the compound with the A and B of the formula.
In a preferred embodiment of the present invention, a material for generating the S or O is a compound containing the A, which is placed upstream of the compound constituting the phosphor to nitride it by calcination.
In a preferred embodiment of the present invention, the compound containing the A is selected from the group consisting of ZnS, ZnSO
4
, ZnO, ZnCO
3
, MgS, MgSO
4
and MgCO
3
.
In a preferred embodiment of the present invention, the A contains Zn in an amount of 0.002 to 1 atm %.
In a preferred embodiment of the present invention, the compound constituting the phosphor is heated at a relatively high temperature and the compound containing the A is heated at a relatively low temperature.
In a preferred embodiment of the present invention, the compound containing the phosphor has a compound containing the A incorporated therein, separately from the compound containing the A placed upstream.
In a preferred embodiment of the present invention, a material for generating the S or O is gaseous and the compound constituting the phosphor is subject to calcination for nitriding in an atmosphere in which the gaseous material is added to the ammonia gas.
In a preferred embodiment of the present invention, gas containing S is selected from the group consisting of H
2
S and SO
2
.
In a preferred embodiment of the present invention, gas containing O is selected from the group consisting of O
2
, O
3
, N
2
O, NO, air, H
2
O, CO
2
and CO.
Also, in accordance with the present invention, a method for preparing a gallium nitride phosphor is provided. The method includes the steps of placing a compound constituting the gallium nitride phosphor in a calcination oven and flowing gas selected from the group consisting of gas containing S and that containing O, and ammonia gas separately from each other in the calcination oven.


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