Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With particular dopant concentration or concentration profile
Reexamination Certificate
1998-06-02
2001-04-24
Jackson, Jr., Jerome (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With particular dopant concentration or concentration profile
C257S088000, C257S096000, C257S097000, C257S091000
Reexamination Certificate
active
06222208
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light-emitting diode and a light-emitting diode array.
2. Description of the Related Art
Light-emitting diode (LED) have conventionally been widely used as display devices because of the brightness of the emitted light, their low driving voltage and the simplicity of the peripheral circuitry, among other reasons. As described for example in N
AKAMURA
Tetsurô and U
CHIMARU
Kiyoshi, Kotai Hakkô-soshi to sono Ôy ô [Solid light-emitting elements and their uses] (Sanpô, 1971), LEDs have hitherto been produced by diffusing impurities on a compound semiconductor substrate to form p-n junctions.
FIG. 1
is a diagram illustrating a typical structure of a conventional LED.
In
FIG. 1
, the LED comprises an n-type GaAs substrate
11
, an n-type GaAsP semiconductor first epitaxial layer
12
grown epitaxially on the n-type GaAs substrate
11
by doping with Te, a p-type GaAsP semiconductor first epitaxial layer
13
formed by diffusing Zn, a SiO
2
insulating film
14
which acts as a mask for Zn diffusion, an Al electrode
15
and an Au—Ge electrode
16
, and is structured in such a manner as to form a p-n junction by diffusing the p-type impurity Zn on the n-type GaAsP substrate. A junction structured in this manner is generally referred to as a homojunction.
LEDs which are structured in this manner have the advantage of being easy to manufacture because relatively few processes are involved. On the other hand, they present a problem in that the wavelength of light produced when the small number of carriers injected through the junction rejoins the larger number of carriers is equal to the energy band gap of the substrate semiconductor. This means that much of the light generated is absorbed in the p-type area as it passes through, with the result that the light-emitting efficiency is not as high as it might be.
In contrast to such LEDs which depend on homojunction, there are others which utilise a p-n junction (hereinafter referred to as a heterojunction) formed by joining different crystals, as is described in O
KUNO
Tadao, Hakkô-daiôdo [Light-emitting diodes] (Sangyô Tosho, 1994). The adoption of a heterojunction allows the light-emitting efficiency of LEDs to be improved above that of homojunctions.
FIGS. 2 and 3
are diagrams illustrating examples of the structure of heterojunction LEDs and their energy band gaps.
FIG. 2
provides an example of an LED of the type generally known as a single heterostructure (SH structure), while
FIG. 3
is an example of the type generally known as a double heterostructure (DH structure).
The single heterostructure LED of
FIG. 2
is formed by growing a p-type Al
0.35
Ga
0.65
As layer epitaxially on a p-type GaAs substrate, and growing an n-type Al
0.35
Ga
0.65
As layer epitaxially on top of that.
In a structure of this sort, as may be seen from FIG.
2
(B), the holes which are injected through the junction are prevented from diffusing by the energy barrier on the surface of the heterojunction, with resulting increase in the rate of recombination. Moreover, the light-emission wavelength is equal to the energy band gap of the Al
0.35
Ga
0.65
As. Since the energy band gap of the n-type Al
0.65
Ga
0.35
As, which is the window for the extraction of light, is greater than that of the Al
0.35
Ga
0.65
As, the emitted light is not absorbed in the semiconductor area which acts as the window. Consequently the light-emitting efficiency increases.
Meanwhile, the double heterostructure LED of
FIG. 3
is formed by sandwiching a p-type Al
0.35
Ga
0.65
As active layer, the light-emitting area, between a p-type Al
0.65
Ga
0.35
As clad layer with an energy band gap greater than that of the active layer on the one hand and an n-type Al
0.65
Ga
0.35
As layer on the other. In a structure of this sort, as may be seen from
FIG. 3
(B), the electrons and holes which are injected through the junction are prevented from diffusing by the energy barrier on the surface of the heterojunction, with resulting increase in the rate of recombination. Moreover, as with the single heterostructure LED, there is no absorption of light in the window area, and the light-emitting efficiency increases. LED arrays, in which the above LEDs are integrated, are used for instance as the light source in LED printers. Where LED arrays with homojunctions are produced, a p-n junction array can easily be manufactured by selective diffusion on to the semiconductor through the diffusion mask orifice. The manufacture of LED arrays by selective diffusion in this manner is a simple process, and it is possible to produce ultra-high-density LEDs of 1200 dpi.
However, if conventional LED arrays of this sort are to be produced with heterojunctions so as to make it possible to improve light-emitting efficiency, each LED needs to be separated by mesa etching for example, and the density of the LED array depends on how this process of separation is controlled. Restrictions on the extent to which the separation process can be controlled impose restrictions on the density of heterojunction LED arrays.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a light-emitting diode which can be arranged in high-density.
In accordance with one aspect of the present invention, the foregoing objects, among others, are achieved by providing
a light-emitting diode comprising: a substrate; a first semiconductor epitaxial layer of a first conduction type formed on or above said substrate; a second semiconductor epitaxial layer of the first conduction type laminated upon the first conductor epitaxial layer and having an energy band gap greater than that of the first semiconductor epitaxial layer; and an area of impurities formed within the first semiconductor epitaxial layer and second semiconductor epitaxial layer by doping impurity of a second conduction type from the side of the second semiconductor epitaxial layer, its front being located within said first semiconductor epitaxial layer.
REFERENCES:
patent: 4037241 (1977-07-01), Dierschke
patent: 4623907 (1986-11-01), Okuda
patent: 4942439 (1990-07-01), Schairer
patent: 4956682 (1990-09-01), Ohnaka
patent: 4982256 (1991-01-01), Suzuki
patent: 5075744 (1991-12-01), Tsui
patent: 5239189 (1993-08-01), Lawrence
patent: 5272362 (1993-12-01), Yagi
patent: 5801404 (1998-09-01), Kahen
patent: 55-63887 (1980-05-01), None
patent: 64-35970 (1989-02-01), None
“Hakko-daiodo” (Light-emitting diodes) (Hetero-junction).
“Kotai Hakko-soshi to Sono Oyo” (Solid light-emitting elements and their uses)(4.2.1 Semiconductor pellet).
Nakamura Yukio
Ogihara Mitsuhiko
Shimizu Takatoku
Taninaka Masumi
Jackson, Jr. Jerome
Jones Volentine, LLC
Oki Data Corporation
LandOfFree
Light-emitting diode and light-emitting diode array does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Light-emitting diode and light-emitting diode array, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Light-emitting diode and light-emitting diode array will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2514561