Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – Plural light emitting devices
Reexamination Certificate
1997-10-09
2001-05-22
Jackson, Jr., Jerome (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
Plural light emitting devices
C257S090000, C257S088000, C257S091000, C372S046012, C372S050121
Reexamination Certificate
active
06236065
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a light-emitting diode (hereinafter, simply referred to as an “LED”) array and a method for fabricating the same. More specifically, the present invention relates to an LED array usable for printing a date on a negative film in a data back unit including a date indicating system for a camera and a method for fabricating the same.
2. Description of the Related Art
Referring to
FIG. 20
, a conventional LED array will be described.
FIG. 20
is a top plan view showing a conventional LED array usable for printing a date on a negative film in a data back unit including a data indicating system for a camera. As shown in
FIG. 20
, a conventional LED array includes seven light-emitting chips
100
arranged in a line. As is apparent from
FIG. 20
, this LED array has a simple structure easily obtained by arranging a plurality of independent light-emitting chips in a line. An electrode is denoted by the reference numeral
101
. Wires connected with the electrode
101
are not shown in FIG.
20
. The size of each light-emitting chip
100
is approximately 300 &mgr;m×300 &mgr;m, for example. The size of the entire LED array, including a substrate on which the LED array is mounted, is approximately 1 mm×4 mm, for example.
Each LED chip for each LED is formed on a single GaP chip, for example. Each LED chip is made of a single GaAs
0.15
P
0.85
. The emission spectrum of each LED chip has a peak in the vicinity of 590 nm. In practical use, this LED array for printing a date on a negative film, a driver IC and a focusing lens are mounted on a substrate.
However, since such a conventional LED array to be used for a data back unit for a camera employs a plurality of single GaAs
0.15
P
0.85
LED chips of an indirect transition type formed on a single GaP chip, the luminous efficiency of these LED chips becomes disadvantageously low. This is why, in order to obtain a sufficient amount of output required for printing a date on a negative film, a current of about 20 mA is required for one LED chip. Therefore, a maximum amount of the current required for printing a date on a negative film reaches 140 mA, i.e., 20 mA×7 chips. In order to supply such an amount of current, it is indispensable to provide a driver IC for an LED array for practical use, as described above. The provision of the driver IC is an obstacle to realizing the objectives of reducing the size of the LED array, the cost necessary for fabricating the LED array and the consumption power necessary for operating the LED array.
On the other hand,
FIG. 21
shows an exemplary semiconductor LED array to be used as an LED printer, as disclosed in Japanese Laid-Open Patent Publication No. 4-100278. The LED array shown in
FIG. 21
uses a direct transition type (Al
x
Ga
1−x
)
y
In
1−y
P (where 0≦x≦1 and 0≦y≦1) layer as an active layer.
As shown in
FIG. 21
, the semiconductor LED array includes: an n-type InGaAlP cladding layer
202
; an InGaAlP active layer
203
; a p-type InGaAlP cladding layer
204
; and a p-type GaAlAs layer
205
. These layers are deposited in this order on a GaAs substrate
201
. In
FIG. 21
, an n-type electrode is denoted by
206
; a GaAs contact layer for forming an electrode is denoted by
207
; a p-type electrode is denoted by
208
; an n-type InGaAlP insulating layer is denoted by
209
; and a bonding pad is denoted by
210
.
Since this structure uses a direct transition type (Al
x
Ga
1−x
)
y
In
1−y
P (where 0≦x≦1 and 0≦y≦1) as the active layer
203
, a relatively high output can be advantageously obtained at a low current value. Therefore, by employing this structure, the reduction in the amount of the current required for printing a date on a negative film in a data back unit for a camera can be expected.
In addition, since this structure applicable to a data back unit for a camera is a monolithic LED array as shown in
FIG. 21
, it is possible to reduce the size of the LED array as compared with the LED array obtained by independently arranging a plurality of light-emitting chips (or elements) in a line as shown in FIG.
20
. Moreover, this structure also makes it possible to reduce the spot diameter of the light emitted from the LED, so that an optical system such as a lens, which has conventionally been required for focusing a spot, is no longer necessary. As a result, the size of the entire system using a data back unit for a camera can be reduced. As compared with a conventional LED array using indirect transition type LED chips shown in
FIG. 20
, the LED array shown in
FIG. 21
surely enables the reduction in the amount of the current required for printing a date on a negative film. However, in order to practically use this LED array for a camera, the maximum amount of the light which can be emitted from this LED array is not sufficiently large for the value of the current required for the emission. Therefore, an LED array allowing for emitting a sufficient amount of light at a lower current value is expected to be developed.
SUMMARY OF THE INVENTION
The light-emitting diode array of the invention including: a semiconductor substrate of a first conductivity type, and a plurality of light-emitting elements linearly arranged on the substrate of the first conductivity type. Each of the plurality of light-emitting elements includes: a cladding layer of the first conductivity type; a cladding layer of a second conductivity type; an (Al
x
Ga
1−x
)
y
In
1−y
P (where 0≦x≦1 and 0≦y≦1) active layer interposed between the cladding layer of the first conductivity type and the cladding layer of the second conductivity type; and a current diffusion layer of the second conductivity type deposited on the cladding layer of the second conductivity type. In the light-emitting diode array, at least the current diffusion layer of the second conductivity type and the cladding layer of the second conductivity type are electrically isolated from each other in two adjacent light-emitting elements among the plurality of light-emitting elements.
In one embodiment, at least the current diffusion layer of the second conductivity type and the cladding layer of the second conductivity type are electrically isolated from each other by performing an etching between the two adjacent light-emitting elements among the plurality of light-emitting elements.
In another embodiment, the light-emitting diode array further includes an insulating layer formed on the current diffusion layer of the second conductivity type.
In still another embodiment, the insulating layer is a SiN
x
layer.
In still another embodiment, the light-emitting diode array further includes: a current blocking layer of the first conductivity type disposed on a side of the current diffusion layer with respect to the active layer; and a window for outputting emitted light formed by partially etching the current blocking layer of the first conductivity type.
In still another embodiment, a band gap of the current blocking layer of the first conductivity type is smaller than a band gap of the active layer.
In still another embodiment, the current blocking layer of the first conductivity type is an (Al
x
Ga
1−x
)
y
In
1−y
P (where 0≦x≦1 and 0≦y≦1) layer.
In still another embodiment, the current blocking layer of the first conductivity type is formed as an uppermost layer of the light-emitting diode array except for electrode portions.
In still another embodiment, the current blocking layer of the first conductivity type is a GaAs layer.
In still another embodiment, a multi-layered reflection film of the first conductivity type is formed between the substrate and the active layer.
In still another embodiment, the multi-layered reflection film of the first conductivity type is a reflection film obtained by alternately depositing
20
pairs each of Al
0.5
In
0.5
P layers and (Al
x1
Ga
1−x1
)
0.5
In
0.5
P layers, where x is a mixed crystal ratio of Al in the active layer and x
Kurahashi Takahisa
Sakata Masahiko
Jackson, Jr. Jerome
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
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