Gallium nitride group compound semiconductor

Details Gallium nitride group compound semiconductor Gallium nitride group compound semiconductor

2000-10-02

2002-10-29

Tran, Minh Loan (Department: 2826)

Active solid-state devices (e.g., transistors, solid-state diode

Incoherent light emitter structure

With particular dopant concentration or concentration profile

C257S102000, C257S103000

Reexamination Certificate

active

06472690

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light-emitting semiconductor device using gallium nitride group compound which emits a blue light.
2. Description of the Prior Art
It is known that GaN compound semiconductor can be made into a light-emitting semiconductor device, such as a light-emitting diode (LED), which emits a blue light. The GaN compound semiconductor attracts attention because of its high light-emitting efficiency resulting from direct transition and of its ability to emit a blue light which is one of three primary colors.
The light-emitting diode manufactured from the GaN compound semiconductor is composed of an n-layer and an i-layer grown thereon. The n-layer of the GaN compound semiconductor with n-type conduction is directly grown on a surface of a sapphire substrate or grown on a buffer layer of aluminum nitride formed on the substrate. The i-layer of insulating (i-type) GaN compound semiconductor doped with p-type impurities is grown on the n-layer. (See Japanese Patent Laid-open Nos. 119196/1987 and 188977/1988.) The light-emitting diode of this structure has room for improvement in luminous intensity. In addition, it comprises no p-n junction but it is made by joining the i-layer and n-layer.
An electric property of the GaN compound semiconductor shows inherently n-type conduction even though it is not deliberately doped with n-type impurities, and unlike silicon and similar semiconductors, when it is doped with zinc of p-type impurities, the electric property shows not p-type conduction but insulation. Moreover, the production of n-type GaN involves many difficulties in controlling conductivity.
SUMMARY OF THE INVENTION
It is the first object of the present invention to improve a luminous efficiency of a GaN group light-emitting diode.
It is the second object of the present invention to provide a new layer structure which improves a luminous efficiency of a GaN group light-emitting diode.
It is the third object of the present invention to provide a technology for production of n-type GaN group compound semiconductor in which conductivity is easily controlled.
After experience in the manufacture of the above-mentioned GaN light-emitting diode, the present inventors established a technology for a vapor phase epitaxy of the GaN group semiconductor with organometal compound. This technology enables a production of a gas-phase grown GaN layer of high purity. In other words, this technology provides n-type GaN with high resistivity without doping with impurities, unlike the conventional technology which provides n-type GaN with low resistivity when no doping is performed.
The First Feature of the Invention
The first feature of the present invention resides in a light-emitting semiconductor device composed of an n-layer of n-type gallium nitride group compound semiconductor (Al
x
Ga
1−x
N; inclusive of x×0) and an i-layer of insulating (i-type) gallium nitride compound semiconductor (Al
x
Ga
1−x
N; inclusive of x×0) doped with p-type impurities, in which the n-layer is of double-layer structure including an n-layer of low carrier concentration and an n
+
-layer of high carrier concentration, the former being adjacent to the i-layer.
According to the present invention, the n-layer of low carrier concentration should preferably have a carrier concentration of 1×10
14
/cm
3
to 1×10
17
/cm
3
and have a thickness of 0.5 to 2 &mgr;m. In case that the carrier concentration is higher than 1×10
17
/cm
3
, the luminous intensity of the light-emitting diode decreases. In case that the carrier concentration is lower than 1×10
14
/cm
3
, since the series resistance of the light-emitting diode increases, an amount of heat generated in the n-layer increases when a constant current is supplied to it. In case that the layer thickness is greater than 2 &mgr;m, since the series resistance of the light-emitting diode increases, the amount of heat generated in the n-layer increases when the constant current is supplied to it. In case that the layer thickness is smaller than 0.5 &mgr;m, the luminous intensity of the light-emitting diode decreases.
In addition, the n
+
-layer of high carrier concentration should preferably contain a carrier concentration of 1×10
17
/cm
3
to 1×10
19
/cm
3
and have a thickness of 2-10 &mgr;m. In case that the carrier concentration is higher than 1×10
19
/cm
3
, the n
+
-layer is poor in crystallinity. In case that the carrier concentration is lower than 1×10
17
/cm
3
, since the series resistance of the light-emitting diode increases, an amount of heat generated in the n
+
-layer increases when a constant current is supplied to it. In case that the layer thickness is greater than 10 &mgr;m, the substrate of the light-emitting diode warps. In case that the layer thickness is smaller than 2 &mgr;m, since the series resistance of the light-emitting diode increases, the amount of heat generated in the n
+
-layer increases when the constant current is supplied to it.
In the first feature of the present invention, it is possible to increase an intensity of blue light emitted from the light-emitting diode by making the n-layer in double-layer structure including an n-layer of low carrier concentration and an n
+
-layer of high carrier concentration, the former being adjacent to the i-layer. In other words, the n-layer as a whole has a low electric resistance owing to the n
+
-layer of high carrier concentration, and hence the light-emitting diode has low series resistance and generates less heat when a constant current is supplied to it. The n-layer adjacent to the i-layer has a lower carrier concentration or higher purity so that it contains a smaller amount of impurity atoms which are deleterious to the emission of blue light from the light-emission region (i-layer and its vicinity). Due to the above-mentioned functions, the light-emitting diode of the present invention emits a blue light of higher intensity.
The Second Feature of the Invention
The second feature of the present invention resides in a light-emitting semiconductor device composed of an n-layer of n-type gallium nitride compound semiconductor (Al
x
Ga
1−x
N; inclusive of x×0) and an i-layer of i-type gallium nitride compound semiconductor (Al
x
Ga
1−x
N; inclusive of x×0) doped with p-type impurities, in which the i-layer is of double-layer structure including an i
L
-layer containing p-type impurities in comparatively low concentration and an i
H
-layer containing p-type impurities in comparatively high concentration, the former being adjacent to the n-layer.
According to the present invention, the i
L
-layer of low impurity concentration should preferably contain the impurities in concentration of 1×10
16
/cm
3
to 5×10
19
/cm
3
and have a thickness of 0.01 to 1 &mgr;m. In case that impurity concentration is higher than 5×10
19
/cm
3
, since the series resistance of the light-emitting diode increases, an initial voltage to start emitting light at increases. In case that the impurity concentration is lower than 1×10
16
/cm
3
, the semiconductor of the i
L
-layer shows n-type conduction. In case that the layer thickness is greater than 1 &mgr;m, since the series resistance of the light-emitting diode increases, the initial voltage to start emitting light at increases. In case that the layer thickness is smaller than 0.01 &mgr;m, the light-emitting diode has the same structure as that of the conventional one.
In addition, the i
H
-layer of high impurity concentration should preferably contain the impurities in concentration of 1×10
19
/cm
3
to 5×10
20
/cm
3
and have a thickness of 0.02 to 0.3 &mgr;m. In case that the impurity concentration is higher than 5×10
20
/cm
3
, the semiconductor of the i
H
-layer is poor in crystallinity. In case that the impurity concentration is lower than 1×10
19
/cm
3
, the luminous intensity of the light-emitting diode decreases. In

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