Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
2000-04-05
2003-12-09
Leung, Quyen (Department: 2828)
Coherent light generators
Particular active media
Semiconductor
C372S045013
Reexamination Certificate
active
06661822
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor light emitting device and a method of manufacturing the same and, more particularly, a semiconductor light emitting device which is employed as a reading/writing light source for a magneto-optic disk device or a light source for a laser printer and a method of manufacturing the same.
2. Description of the Prior Art
As the group III nitride semiconductor laser, the ridge type semiconductor laser which is formed by the steps without dry-etching the active layer and re-growing the crystal of the current constricting layer, etc. and thus can be formed simply are extensively employed.
For example, as disclosed in Patent Application Publication (KOKAI) Hei 4-242985, there is the semiconductor laser which has a GaN compound semiconductor layer as such ridge type group III nitride semiconductor laser.
As the ridge type semiconductor laser, there is the semiconductor laser which has a structure as shown in
FIGS. 1A and 1B
.
First, in the semiconductor laser shown in
FIG. 1A
, a buffer
112
made of aluminum nitride (AlN) and a first cladding layer
113
made of n-type aluminum gallium nitrogen (AlGaN) are formed on a sapphire substrate
111
by the MOVPE (metal organic vapor-phase epitaxy) method. Then, a part of a surface of the first cladding layer
113
is covered with a silicon dioxide (SiO
2
) film (not shown), and then an active layer
114
made of GaP and a second cladding layer
115
made of p-type AlGaN are formed in sequence on a region of the first cladding layer
113
, which is not covered with the SiO
2
film, by the MOVPE method.
Then, the SiO
2
film is removed by hydrofluoric acid, and then another SiO
2
film
116
is formed on the second cladding layer
115
. An window
116
a
for electrode connection is formed in the SiO
2
film
116
by the photolithography method.
Then, a p-side electrode
117
and an n-side electrode
118
are formed on the second cladding layer
115
exposed from the window
116
a
and the first cladding layer
113
located on the side of the cladding layer
115
respectively.
With the above steps, a basic structure of the ridge type GaN semiconductor laser diode can be completed.
By the way, the substrate used in the ridge type semiconductor laser is not limited to sapphire, and a silicon carbide (SiC) substrate may be used. An example of such SiC substrate will be explained. with reference to FIG.
1
A.
At first, an n-type AlGaN cladding layer
122
, an n-type GaN SCH layer
123
, an InGaN active layer
124
, a p-type GaN SCH layer
125
, a p-type AlGaN cladding layer
126
, and a p-type GaN contact layer
127
are formed in sequence on an SiC substrate
121
by the MOVPE method.
Then, a stripe-like SiO
2
film (not shown) is formed on the contact layer
127
, and then the p-type GaN contact layer
127
and the p-type AlGaN cladding layer
126
are selectively removed in sequence by the well-known dry etching method while using the SiO
2
film as a mask, whereby the p-type GaN SCH layer
125
is exposed from both sides of the stripe-like SiO
2
film.
Then, the SiO
2
film is removed and then another SiO
2
film
128
is formed. Then, a contact hole
128
a
is formed on the contact layer
127
by patterning another SiO
2
film
128
by using the well-known photolithography method.
Then, a p-side electrode
129
is formed on the contact layer
127
via the contact hole
128
a
, and also an n-side electrode
130
is formed under the SiC substrate
121
.
With the above steps, a basic structure of the ridge type GaN semiconductor laser diode using SiC as the substrate can-be completed.
In this manner, a heat sink effect can be expected. by the semiconductor laser using the SiC substrate rather than the semiconductor laser using the sapphire substrate. Also, since the n-side electrode can be provided on the substrate side, the chip mounting technology as applied to the normal semiconductor laser, etc. can be employed. In addition, since the semiconductor laser using the SiC substrate can have the cleavage property by selecting appropriately the face orientation of the SiC substrate, the Fabry-Perot reflection surface can be formed easily in contrast to the semiconductor laser using the sapphire substrate.
In the semiconductor laser using the group III nitride film compound semiconductor in the prior art, the ridge structure must be employed to form the electrode thereon and also the width of the ridge is restricted by the area of the electrode because of the necessity to assure the alignment margin of the electrode.
There is such a problem that, if the width of the ridge exceeds 2 &mgr;m, the optical confinement is weakened in the lateral direction and thus the beam shape is laterally elongated.
A method of performing the optical confinement without the ridge structure or a semiconductor laser in which the current constricting layer is formed is disclosed in Patent Application Publication (KOKAI) Hei 10-294529, Patent Application Publication (KOKAI) Hei 9-232680, and Patent Application Publication (KOKAI). Hei 8-88441.
In Patent Application Publication (KOKAI) Hei 10-294529, an example in which the optical confinement layer is formed on the side of the ridge on the p-type cladding layer and the light is confined by utilizing difference in the refractive index is set forth. It is disclosed to employ InGaN, which has the larger refractive index than the p-type cladding layer, as material of the optical confinement layer. There is such a disadvantage that higher modes are ready to occur if such material having the large refractive index is employed.
In Patent Application Publication (KOKAI) Hei 8-97502, an example in which the current blocking layer is formed in the p-type cladding layer is set forth. The material is InGaN, silicon, etc. This example has a feature to employ the optical absorbing material, but control of the lateral mode is not enoughly performed. In addition, since the photolithography method is employed to form the current path in the current blocking layer, the light emitting portion of the active layer under the current blocking layer is subjected to etching damage if the dry etching is used as the photolithography method, and thus the light emitting characteristic is degraded.
Further, in Patent Application Publication (KOKAI) Hei 9-232680, an example in which the AN, layer is employed as the current constricting layer is set forth, and has a structure to bury both sides of the ridge of the cladding layer by the AlN layer. Such structure cannot help increasing the width of the cladding layer to assure the contact region to the p-side electrode, like the structure shown in FIG.
1
B. In addition, the film thickness of the AlN layer is equal to or more than the cladding layer and is thick such as 1 &mgr;m. Therefore, the optical confinement is excessively enhanced and thus the higher modes easily occur.
Besides, in Patent Application Publication (KOKAI) Hei 8-88441, an example in which the AlN layer is formed between the p-type cladding layer and the p-type contact layer as the current constricting layer is set forth. However, this example cannot effectively perform the lateral mode control.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a semiconductor light emitting device in which contact to an electrode is set arbitrarily and large and which is ready to control a lateral mode to a desired width, and a semiconductor light emitting device manufacturing method including the step of forming a lateral mode control structure without damage of a current path of an active layer.
According to the present invention, the AlN layer having a thickness of more than 0 nm but less than 300 nm is inserted into the cladding layer, which is formed on or under the active layer made of the group III-V nitride, as the lateral mode controlling layer. The lateral mode controlling layer also acts as the current constricting later.
The AlN layer can reduce difference in the refractive index from the cladding layer in contr
Horino Kazuhiko
Kubota Shin'ichi
Kuramata Akito
Leung Quyen
Westerman Hattori Daniels & Adrian LLP
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