Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal
Reexamination Certificate
2002-05-03
2003-07-22
Mulpuri, Savitri (Department: 2812)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
C438S555000, C438S558000
Reexamination Certificate
active
06596556
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light emitting diode, and particularly to a light emitting diode having a structure capable of heightening the optical output and a method for manufacturing the same.
2. Description of Related Art
A light emitting diode array in which planar-type light emitting diodes (LEDs) are arranged in an array has been put to practical use for an LED printer and the like. An example of the fundamental structure of such a former light emitting diode array is briefly described with reference to FIG.
7
and FIGS.
8
(A) to
8
(C). The light emitting diode array
10
is provided with an insulating film
16
on one main surface (upside)
12
a
of an n-type semiconductor region
12
. The insulating film
16
has a plurality of diffusion windows
20
formed by etching. These diffusion windows
20
are arranged at regular intervals in a line. This array
10
has individual p-type diffusion regions, namely, p-type semiconductor regions
28
each of which is formed by diffusing zinc (Zn) as an impurity into an n-type semiconductor region
12
exposed in a diffusion window
20
. The p-type semiconductor region
28
is an island-shaped surface-diffused region surrounded by the n-type semiconductor region
12
, and the respective upsides
12
a
and
28
a
of the n-type and p-type semiconductor regions are in a common plane. The junction
30
between both the regions is in the shape of a dish. Ordinarily, the p-type semiconductor regions adjacent to each other are isolated from each other. Individual p-side electrodes
24
electrically connected to the respective p-type semiconductor regions are formed on the insulating film
16
. An n-side electrode
26
is formed on the other main surface (reverse side) of the insulating film
16
.
FIG. 8
shows part of the former light emitting diode array, focusing on one LED. Particularly, FIG.
8
(A) is a sectional view taken along line X-Y of FIG.
7
. FIG.
8
(B) is a plan view mainly showing the p-type semiconductor region exposed in the diffusion window
20
. FIG.
8
(C) is an optical output characteristic curve diagram for explaining an output characteristic of this LED, and the abscissa shows a position and the ordinate shows an optical output (in an arbitrary unit).
The p-type semiconductor region
28
described above comprises a first partial region R
1
which is constant in depth (thickness) from its upper surface
28
a
and a second partial region (also referred to as a peripheral region) R
2
which is its peripheral region and is shallower (thinner) than the first partial region R
1
in depth (thickness) from the upper surface
28
a
. Since the junction
30
a
of the first partial region R
1
in the junction interface is substantially in parallel with the upper surface, the depth of the junction has a constant value L
1
. On the other hand, the junction
30
b
of the second partial region R
2
becomes gradually shallower as it becomes more distant from the first partial region R
1
. Finally, the junction
30
b
ends at the boundary between the upper surfaces
12
a
and
28
a
(the peripheral edge of the p-type semiconductor region
28
) R
20
.
Therefore, the thickness of the second partial region R
2
gradually varies from depth L
1
to depth “0” according to a position in it.
When letting an electric current flow between both the electrodes
24
and
26
of an LED
10
having such a structure as this, electrons and holes are recombined in the junction
30
to generate light. Generated light B passes through the p-type semiconductor region
28
and is outputted from the diffusion window
20
(see FIG.
7
).
Hereupon, the light B
1
generated at the junction
30
a
of the first partial region R
1
passes through said first partial region R
1
being thicker in thickness and then is outputted. The light B
2
generated at the junction
30
b
of the second partial region R
2
passes through said second partial region R
2
being thinner in thickness and then is outputted. Now, it is assumed that a quantity of light generated in a unit area of the junction interface is constant. The generated light passes through these first and second partial regions R
1
and R
2
in the direction perpendicular to the upper surface of these regions. In this case, a quantity of light absorbed in these partial regions is the maximum in the first partial region R
1
. A quantity of light absorbed in the second partial region R
2
is the maximum at the boundary between the first and second partial regions and is “0” at the peripheral edge R
20
of the second partial region R
2
. It becomes gradually smaller as being closer to the peripheral edge R
20
in the intermediate portion of the second partial region.
It is therefore known that the power of light outputted from the upper surface
28
a
of the p-type semiconductor region
28
is the minimum I
0
in the first partial region R
1
, and becomes gradually larger so that it is the maximum I
0+i
(>I
0
) at the peripheral edge R
20
in the second partial region R
2
(see FIG.
8
(C)).
In a former LED having a structure like this, as described above, since light is absorbed in the p-type semiconductor region, the total optical power of outputted light is made smaller. Thereupon, up to now a desired large optical power has been obtained by applying a high voltage between the n-side and p-side electrodes
24
and
26
, but applying a high voltage as described above has caused a problem that the power consumption becomes high.
SUMMARY OF THE INVENTION
As a result of various attempts at solving this problem, the inventors have found that if part of the junction of the second partial region, which has been up to now formed so as to be constant in depth from the upper surface, is formed as a shallower junction, absorption of light can be reduced corresponding to the depth becoming shallower, and thereby have attained the present invention.
Thus, an object of the present invention is to provide a light emitting diode capable of outputting a high-power light without applying a high voltage between the electrodes.
Another object of the invention is to provide a method for manufacturing such a light emitting diode.
In order to attain the objects, according to a first aspect of the present invention, there is provided a light emitting diode (LED) provided with such a structure as described below. This LED is provided with a first conductive-type semiconductor region and a second conductive-type semiconductor region which is buried in the first conductive-type semiconductor region and forms a junction with the first conductive-type semiconductor region. The junction at the bottom of the second conductive-type semiconductor region (said junction being here referred to as a bottom junction) varies in depth from the surface of the second conductive-type semiconductor region according to a position in it.
According to such a structure, when making the maximum depth of the bottom Junction of the second conductive-type semiconductor region coincide with the depth of the bottom junction of a former LED, a junction depth at another position in the bottom is shallower than this maximum depth. Therefore, the bottom junction includes a deep junction and a shallow junction. This means that the second conductive-type semiconductor region includes a deep portion and a shallow portion, in other words, that a place where generated light is more absorbed and a place where generated light is less absorbed. Absorption of light depends upon the thickness of the second conductive-type semiconductor region which the light passes through. Accordingly, even if an electric current of high density does not flow between the electrodes by applying between them a high voltage . By this, it is possible to heighten a quantity of output light, namely, an optical power of the LED corresponding to a reduction in absorption of light in the second conductive-type semiconductor region.
In implementing the present invention, the second conductive-type semiconductor region preferably
Burdett James R.
Mulpuri Savitri
Oki Electric Industry Co. Ltd.
Venable
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