Method for fabricating semiconductor light emitting element

Details Method for fabricating semiconductor light emitting element Method for fabricating semiconductor light emitting element

2001-04-23

2002-06-04

Fourson, George (Department: 2823)

Semiconductor device manufacturing: process

Making device or circuit emissive of nonelectrical signal

Compound semiconductor

C438S047000, C438S483000, C438S518000, C438S590000, C438S604000

Reexamination Certificate

active

06399409

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor light emitting element. More particularly, the present invention relates to a structure of, and a method for fabricating, a quadruple alloy light emitting diode (LED) made of a quadruple alloy material of AlGaInP for constituting a high-luminescence LED which emits light in a red to green band.
2. Description of the Related Art
In recent years, a high-luminance quadruple alloy LED made of AlGaInP has become the object of particular attention as a light emitting element for various types of display devices for indoor use and outdoor use. A quadruple alloy material allows for the fabrication of an LED which emits light in a wide visible wavelength region ranging from a red to green band.
A typical structure of a conventional quadruple alloy LED
1100
for a yellow band is shown in FIGS.
7
A and
7
B:
FIG. 7A
is a perspective view thereof; and
FIG. 7B
is a schematic cross-sectional view thereof.
In this structure, an n-(Al
0.7
Ga
0.3
)
0.5
In
0.5
P cladding layer
51
(doped with Si, carrier concentration: about 5×10
17
cm
−3
, thickness: about 1.5 &mgr;m), a non-doped (Al
0.3
Ga
0.7
)
0.5
In
0.5
P active layer
52
(thickness: about 0.7 &mgr;m), a p-(Al
0.7
Ga
0.3
)
0.5
In
0.5
P cladding layer
53
(doped with Zn, carrier concentration: about 5×10
17
cm
−3
, thickness: about 1.5 &mgr;m), a p-Al
0.7
Ga
0.3
As current diffusion layer
54
(doped with Zn, carrier concentration: about 3×10
18
cm
3
, thickness: about 5 &mgr;m), and a p-GaAs ohmic contact layer
55
(doped with Zn, carrier concentration: about 3×10
18
cm
−3
, thickness: about 0.5 &mgr;m) are sequentially formed in this order on an n-GaAs substrate
50
by metal organic chemical vapor deposition (MOCVD). In addition, lower and upper electrodes
56
and
57
are formed on the reverse surface of the substrate
50
and on the top surface of the grown layered structure, respectively. The upper electrode
57
on the top surface of the grown layered structure, as well as the p-GaAs ohmic-contact layer
55
, have been patterned so as to be in a circular shape in the center region of the top surface of the structure. Portions of the upper electrode
57
and the pGaAs ohmic contact layer
55
have been removed by performing an etching, leaving the circular-shaped portions remaining in the center region.
An axial luminous intensity (unit: candela (cd)) of a molded LED element is one of the indices representing the luminescence of the LED. In the conventional LED
1100
shown in
FIGS. 7A and 7B
, when the axial spread angle of the emitted light is about ±4 degrees with an operating voltage of about 2.0 V and a drive current of about 20 mA, the axial luminous intensity is about 8 cd.
The apparent axial luminous intensity is increased as the light concentration characteristics of an LED are improved (i.e., as the axial spread range of the emitted light is smaller). Moreover, an LED having improved light concentration characteristics can be advantageously used for communication applications.
Another conventional LED
1200
, for communication, is shown in FIGS.
8
A and
8
B:
FIG. 8A
is a perspective view thereof; and
FIG. 8B
is a schematic cross-sectional view taken along the line
8
B-
8
B′ of the LED
1200
shown in FIG.
8
A. The conventional LED
1200
shown in
FIGS. 8A and 8B
is an AlGaInP alloy system LED for a yellow band and has the following structure.
As shown in the schematic cross-sectional view in
FIG. 8B
, an n-(Al
0.7
Ga
0.3
)
0.5
In
0.5
P cladding layer
51
(doped with Si, carrier concentration: about 1×10
18
cm
−3
, thickness: about 1.0 &mgr;m), a non-doped (Al
0.3
Ga
0.7
)
0.5
In
0.5
P active layer
52
(thickness: about 0.6 &mgr;m), a p-(Al
0.7
Ga
0.3
)
0.5
In
0.5
P cladding layer
53
(doped with Zn, carrier concentration: about 1×10
18
cm
−3
, thickness: about 1.0 &mgr;m), an n-(Al
0.7
Ga
0.3
)
0.5
In
0.5
P current constriction layer
58
(doped with Si, carrier concentration: about 2×10
18
cm
−3
, thickness: about 0.4 &mgr;m), a p-Al
0.7
Ga
0.3
As current diffusion layer
54
(doped with Zn, carrier concentration: about 3×10
18
cm
−3
, thickness: about 6 &mgr;m), and a p-GaAs ohmic contact layer
55
(doped with Zn, carrier concentration: about 3×10
18
cm
3
, thickness: about 0.5 &mgr;m) are sequentially formed in this order on an n-GaAs substrate
50
by MOCVD.
The center region of the n-(Al
0.7
Ga
0.3
)
0.5
In
0.5
P current constriction layer
58
has been etched away in a circular shape to form a light emitting region, and the p-Al
0.7
Ga
0.3
As current diffusion layer
54
is re-grown over the current constriction layer
58
including the etched and removed center region thereof. The reference numeral
59
denotes the re-growth interface.
In addition, lower and upper electrodes
56
and
57
are formed on the reverse surface of the substrate
50
and on the top surface of the grown layered structure, respectively. The upper electrode
57
and the p-GaAs ohmic contact layer
55
are formed in a doughnut shape in which the center regions thereof are etched away so as to have openings of the same size and shape as those of the etched and removed region of the current constriction layer
58
.
In this conventional LED element
1200
, an injected current flows in a concentrated manner into the center region, so that the reduced spot size of emitted light can be realized. As a result, the light concentration characteristics of the resulting element, which has been molded with a resin, can be improved and the axial luminous intensity thereof can be increased.
However, in the conventional LED
1200
shown in
FIGS. 8A and 8B
, the p-Al
0.7
Ga
0.3
As current diffusion layer
54
is re-grown on the underlying p-(Al
0.7
Ga
0.3
)
0.5
In
0.5
P cladding layer
53
containing Al. Thus, oxygen is likely to be absorbed into the re-growth interface
59
(see FIG.
8
B), resulting in various losses such as adversely increased resistance and non-radiative recombination of injected carriers.
The typical operational characteristics of such a conventional LED
1200
are as follows: the axial spread angle is about ±2 degrees and the luminescence is about 16 cd with the operating voltage of about 3.0 V when a power of about 20 mA is supplied thereto. As compared with the conventional LED
1100
shown in
FIGS. 7A and 7B
(which is made of the same quadruple alloy material and has the axial spread angle of about ±4 degrees and the luminescence of about 8 cd with the operating voltage of about 2.0 V when a power of about 20 mA is supplied thereto), the axial luminous intensity of the LED
1200
shown in
FIGS. 8A and 8B
is increased only by as little as twofold while the operating voltage is considerably increased. In the element
1200
shown in
FIGS. 8A and 8B
, the luminescence has been expected to be increased fourfold (i.e., about 32 cd) since the axial spread angle thereof is decreased to about ½ of that of the element
1100
shown in
FIGS. 7A and 7B
.
In order to solve such problems as set forth above, another conventional semiconductor light emitting element
1300
having such a structure as that shown in
FIG. 9
has been suggested. The shape of the current constriction layer and the electrode on the top surface of the grown layered structure of the semiconductor light emitting element
1300
shown in
FIG. 9
is the same as that of the element
1200
shown in
FIGS. 8A and 8B
.
As shown in the schematic cross-sectional view in
FIG. 9
, an n-(Al
0.7
Ga
0.3
)
0.5
In
0.5
P cladding layer
51
(doped with Si, carrier concentration: about 1×10
18
cm
−3
, thickness: about 1.0 &mgr;m), a non-doped (Al
0.3
Ga
0.7
)
0.5
In
0.5
P active layer
52
(thickness: about 0.6 &mgr;m), and a p(Al
0.7
Ga
0.3
)
0.5
In
0.5
P cladding layer
53
(doped with Zn, carrier concentration: about 1×10
18
cm
−3
thickness: about 1.0 &mgr;m) are sequentially formed in this o

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