Light emitting semiconductor device with stacked structure

Details Light emitting semiconductor device with stacked structure Light emitting semiconductor device with stacked structure

1998-06-09

2001-01-30

Tran, Minh Loan (Department: 2811)

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

Incoherent light emitter structure

With heterojunction

C257S079000, C257S096000

Reexamination Certificate

active

06180961

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention concerns a light emitting semiconductor device, such as a light emitting diode device, and a light emitting semiconductor device array.
2. Description of the Related Art
Light emitting diode (LED) devices have been widely employed as display devices for some time because the light which they emit is brilliant, the drive voltage is low, and the peripheral circuitry is simple.
Conventionally, the LED arrays used in photo printers are such as are disclosed, for example, in
Hikari Purinta Sekkei
(
Photo Printer Design
), pp 121-126, ed. by Y. Takekida, Torikeppusu KK, Oct. 31, 1985. Conventionally these have been fabricated by selectively diffusing zinc on a substrate made by epitaxial growth of GaAsP on a GaAs substrate (hereinafter called a GaAsP
−
substrate).
FIG. 14
is a diagram which models conventional LED fabrication. This LED comprises an n-type GaAs substrate
11
, an n-type GaAsP epitaxial layer
12
wherein Te is doped and epitaxially grown on the n-type GaAs substrate
11
, a p-type GaAsP epitaxial region
13
formed by diffusing Zn, a SiN insulating film
14
which functions as a mask for Zn diffusion, an Al electrode
15
, and an Au—Ge electrode
16
. This LED is structured by the formation of a pn junction by diffusing zinc, which is a p-type impurity, in an n-type GaAsP substrate. Junctions having this structure are commonly called homo junctions.
LEDs structured in this way provide the advantages of requiring comparatively few fabrication steps and of being easy to fabricate. In such LEDs as these, the minority carriers injected through the junction recombine with the majority carriers and emit light. The wavelength of this emitted light corresponds to the energy band gap of the substrate semiconductor. For this reason, the light emitted is affected by large light absorption in the p-type region as it passes through, wherefore the light emission efficiency is not high, which is a problem.
In distinction to LEDs based on the homo junction, as described above, there are LEDs which use a pn junction (hereinafter called a hetero junction) formed by joining a different crystal, such as is set forth, for example, in
Hakko Daiodo
(
Light
-
Emitting Diodes
), pp. 27-31, Okuno, Sangyou Tosho KK, Jan. 20, 1994. As will be described subsequently, the light emission efficiency of an LED can be made higher with a hetero junction than with a homo junction.
FIG.
15
(A) is a diagram of the structure of an LED using the hetero structure, while FIG.
15
(B) is a diagram of an example of an energy band gap therein.
FIG. 15
is a diagram of an example of an LED commonly called a single hetero structure (SH structure).
The LED having the single hetero structure shown in FIG.
15
(A) is structured with a p-type Al
0.35
Ga
0.65
As layer
21
epitaxially grown on a p-type GaAs substrate
20
, with an Al
0.65
Ga
0.35
As layer
22
grown epitaxially on top of that. Reference numerals
23
and
24
show Au electrodes, respectively.
With this structure, as shown in FIG.
15
(B), the positive holes injected through the junction are blocked from diffusing by the energy barrier at the hetero junction interface, whereupon the proportion that recombines increases. The wavelength of the light emitted, moreover, corresponds to the energy band gap of the Al
0.35
Ga
0.65
As layer
21
, while the n-type Al
0.65
Ga
0.35
As layer
22
that forms a light window is larger than the energy band gap of the Al
0.35
Ga
0.65
As layer
21
, so the emitted light is not absorbed in the semiconductor region
22
that constitutes the window. Accordingly, the light emission efficiency increases.
LED arrays in which the LEDs described above are integrated are used as light sources in LED printers, for example. When an LED array is fabricated by homo junctions, pn junction arrays can be easily fabricated by selective diffusion in which the diffusion into the semiconductor is performed through the diffusion mask openings. The fabrication of LED arrays by this selective diffusion is easy, and it is possible to fabricate a super-high-density 1200 dpi LED array.
With a conventional hetero structured LED such as this, a semiconductor layer having an energy band gap larger than the energy of the light forms a window, so there is no light absorption, and the efficiency with which the light is drawn to the outside is enhanced. On the other hand, with an LED array using LEDs of this structure, it is necessary to provide device separation between the devices. For that purpose, the elements are separated, for example, by mesa etching. This places limitations on the integration density of the LED array.
Thus, in the related art, there is no technology for fabricating LED arrays that exhibit high light emission efficiency and are capable of super-high-density integration.
An object of the present invention is to provide both a light emitting semiconductor device and a light emitting semiconductor device array that exhibit high light emission efficiency and wherewith high densities can be achieved.
Another object of the present invention is to provide both a light emitting semiconductor device and a light emitting semiconductor device array that can be mass-produced at low cost and high yield.
SUMMARY OF THE INVENTION
A first aspect of the present invention is a light emitting semiconductor device having the following construction. First, a laminated or stacked structure is formed that comprises at least, on a substrate, a semiconductor layer having an energy band gap, and, beneath that semiconductor layer, a first conductivity type semiconductor layer having a relatively smaller energy band gap than that of aforesaid semiconductor layer. A pn junction face is formed selectively in the first conductivity type semiconductor layer. In addition, the laminated or stacked structure described above, including the first conductivity type semiconductor layer, contains at least one layer that is a semi-insulating layer of an undoped semiconductor layer.
As based on this light emitting semiconductor device structure, this semiconductor laminated or stacked structure exhibits enhanced light emission efficiency, for the following reasons. First, it is a hetero-epitaxial structure. Second, injected electrons can be contained or confined between the pn junction face provide din the first conductivity type semiconductor layer and the lamination interface between that semiconductor layer and the semiconductor layer on top of it, whereupon the injection electron density rises, so that the recombination probability increases. Third, the wavelength of the emitted light is determined by the energy band gap of the first conductivity type semiconductor layer, but the energy band gap of the semiconductor layer above, which constitutes a light emission window, is large, so the emitted light is not absorbed.
As based on this light emitting semiconductor device structure, moreover, the laminated or stacked structure described above can be formed so as to be thin, and the pn junction can also be formed so that it is locally shallow, so that no wide device separation space is required for forming selectively the pn junction regions in the first conductivity type semiconductor layers, making it possible to raise the light emitting semiconductor device density, but wide device separation space is required for mesa-etched grooves or the like between the light emitting semiconductor devices.
A second aspect of the present invention is a light emitting semiconductor device having the following construction. In the first place, a laminated or stacked structure is provided wherein semiconductor layers having energy band gaps are positioned on and beneath a first conductivity type semiconductor layer having a relatively smaller energy band gap than those of aforesaid semiconductor layers. A second conducting impurity diffusion region is formed that extends from the upper surface of the outermost semiconductor layer provided above in the laminated or stacked structure to within the firs

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