Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure
Reexamination Certificate
1999-05-17
2001-11-06
Lee, Eddie (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
C257S095000, C257S081000, C257S082000, C257S083000, C257S084000, C257S102000, C257S184000, C372S045013
Reexamination Certificate
active
06313483
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a light-emitting semiconductor device such as a light-emitting diode.
A conventional light-emitting diode, referred to below as an LED, is formed by selective diffusion of a p-type impurity into an n-type semiconductor substrate.
FIG. 1
shows an example In which the semiconductor substrate
10
comprises an n-type gallium-arsenide (GaAs) substrate layer
11
and an n-type gallium-arsenide-phosphide (GaAsP) epitaxial layer
12
. Selective diffusion of zinc (Zn) creates a p-type diffusion region
14
. The device is covered with an insulating film
15
in which a window is opened to permit a p-electrode
16
to make contact with the diffusion region
14
. An n-electrode
17
is formed on the underside of the device, in contact with the n-type GaAs substrate
11
. When a forward voltage is applied between the p-electrode
16
and n-electrode
17
, light is emitted by radiative recombination of electrons and holes in the vicinity of the pn junction formed between the p-type diffusion region
14
and the n-type GaAsP epitaxial layer
12
.
Nonradiative recombination also occurs, especially near the surface of the device, due to crystal defects present near the surface.
FIG. 2
shows a variation of this device in which the semiconductor substrate
20
has three epitaxial layers: an n-type GaAs
1−x
P
x
graded buffer layer
21
in which the phosphorus concentration (the value of x) gradually increases in the upward direction; an n-type GaAs
1−y
P
y
layer
22
in which the phosphorus concentration (y) is constant; and an n-type GaAs
1−z
P
z
layer
23
in which the phosphorus concentration (z) is constant and is greater than the concentration (y) in the GaAs
1−y
P
y
layer
22
. The p-type zinc diffusion
24
extends through the GaAs
1−z
P
z
layer
23
into the GaAs
1−y
P
y
layer
22
. Because of the different phosphorus concentrations, light emitted in the GaAs
1−y
P
y
layer
22
is not absorbed in the GaAs
1−z
P
z
layer
23
, so light emission is increased.
A problem in these conventional LEDs is that the p-type impurity (zinc) diffuses laterally as well as vertically, and near the surface of the device, the lateral diffusion is irregular. In the device in
FIG. 2
, in particular, the diffusion front becomes extremely irregular on a microscopic scale at the interface between the GaAs
1−z
P
z
layer
23
and the GaAs
1−y
P
y
layer
22
. The irregularities create strong electric field pockets, so that when a forward voltage is applied, much of the forward current is channeled across the pn junction at points near the surface (in the GaAs
1−z
P
z
layer
23
in
FIG. 2
, for example), where nonradiative recombination is most likely to occur. The light-emitting efficiency of the device is thereby reduced.
SUMMARY OF THE INVENTION
An object of the present invention is to increase the efficiency of a light-emitting semiconductor device by reducing nonradiative recombination.
A light-emitting semiconductor device according to a first aspect of the invention is formed in a semiconductor substrate having a conductive semiconductor layer of a first conductive type, and a semi-insulating semiconductor surface layer adjacent the conductive semiconductor. A first diffusion region, of a conductive type opposite to the first type, is formed in both of these layers, the depthwise diffusion front ending in the conductive semiconductor layer. A second diffusion region, of the first conductive type, is also formed, extending through the semi-insulating semiconductor surface layer at least to the interface between that layer and the conductive semiconductor layer. A first electrode forms an ohmic contact with the first diffusion region. A second electrode forms an ohmic contact with the second diffusion region.
A light-emitting semiconductor device according to a second aspect of the invention is similar, but the semi-insulating semiconductor surface layer is etched, leaving only an island disposed in the first diffusion region, and no second diffusion region is provided. The second electrode forms an ohmic contact directly with the conductive semiconductor layer.
The invention also provides arrays of light-emitting semiconductor devices of the above types, and in particular, matrix-driven arrays.
Since the semi-insulating semiconductor surface layer has no pn junction, recombination tends not to occur near the surface of the device. Nonradiative recombination is thereby reduced.
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Hamano Hiroshi
Ogihara Mitsuhiko
Taninaka Masumi
Frank Robert J.
Lee Eddie
Lee Eugene
Oki Data Communication
Sartori Michael A.
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