Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
1998-04-30
2001-04-10
Arroyo, Teresa M. (Department: 2881)
Coherent light generators
Particular active media
Semiconductor
C372S045013
Reexamination Certificate
active
06215803
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gallium nitride group compound semiconductor light-emitting device and a method for producing the same. More particularly, the present invention relates to a gallium nitride group compound semiconductor light-emitting device, which is preferable as a gallium nitride group compound semiconductor laser and a gallium nitride group compound semiconductor light-emitting diode, capable of emitting light from the blue region to the ultraviolet region of the spectrum; and a method for producing the same.
2. Description of the Related Art
FIG. 7
shows one example of a conventional compound semiconductor laser device. This compound semiconductor laser device is an InGaAlP group compound semiconductor laser having an internal current blocking layer. Such a semiconductor laser is disclosed in, for example, Japanese Laid-Open Publication No. 62-200786.
The structure of this semiconductor laser will now be described together with a production method thereof. First, an N-type GaAs buffer layer
201
, an N-type InGaP buffer layer
202
, and an N-type InGaAlP cladding layer
203
are formed in this order on an N-type GaAs substrate
200
in a metal organic chemical vapor deposition (MOCVD) apparatus. Then, an InGaP active layer
204
is formed on the n-type InGaAlP cladding layer
203
.
Next, a P-type InGaAlP cladding layer
205
(
205
a
and
205
b
) including an etching stopper layer
205
′, a P-type InGaAlP contact layer
206
and a P-type GaAs contact layer
207
are formed on the InGaP active layer
204
.
Then, an N-type GaAs current blocking layer
208
and a P-type GaAs contact layer
207
(
207
a
and
207
b
) are sequentially formed. Thereafter, a P-side electrode
209
and an N-side electrode
210
are formed. In this manner, the InGaAlP group compound semiconductor laser device having a waveguide structure and an internal current blocking layer is completed.
This type of InGaAlP group compound semiconductor laser device has the following problems due to the production method thereof.
More specifically, the method for producing this type of semiconductor laser device requires, during the production process (i.e., after the contact layer
206
has been formed), the steps of taking out the N-type GaAs substrate
200
having semiconductor layers stacked thereon (i.e., wafer) from the MOCVD apparatus; etching the P-type InGaAlP cladding layer
205
by wet etching or dry etching to form a stripe-shaped projection; placing the wafer with a surface of the P-type InGaAlP cladding layer
205
being exposed again in the MOCVD apparatus; and regrowing the N-type GaAs current blocking layer
208
on a portion of the exposed surface of the InGaAlP cladding layer
205
. In the regrowth step, a substrate temperature needs to be raised to about 700° C.
As a result, during a rise in the substrate temperature, surface roughness at the exposed surface of the P-type InGaAlP cladding layer
205
is increased. Moreover, the width W of the striped-shaped projection as well as the distance t between the N-type GaAs current blocking layer
208
and the InGaP active layer
204
are changed.
Consequently, in a compound semiconductor laser having such a structure as described above, the crystallinity of the regrown internal current blocking layer is deteriorated. Moreover, both the width W of the stripe-shaped projection and the distance t between the current blocking layer and the active layer are changed, as described above. Thus, electrical and optical characteristics of the semiconductor laser are deteriorated, making the semiconductor laser less reliable.
The above-described problems occur also in a gallium nitride group compound semiconductor light-emitting device.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, a gallium nitride group compound semiconductor light-emitting device including a layered structure on a substrate; the layered structure including: an active layer; a first cladding layer and a second cladding layer with the active layer interposed therebetween, the second cladding layer being located further away from the substrate than the first cladding layer, and having a stripe-shaped projection; a surface protecting layer and an internal current blocking layer which are formed on the second cladding layer and have an opening at a position corresponding to a position on the stripe-shaped projection; and a regrowth layer which covers both the internal current blocking layer and an exposed surface of the second cladding layer to the opening, wherein the surface protecting layer serves to prevent evaporation of Ga, N or impurity elements from the second cladding layer in a process including forming the internal current blocking layer, is provided.
In one embodiment, the substrate is conductive or non-conductive, i.e., not a semiconductor, the surface protecting layer is made of Al
z
Ga
1-z
N (where 0≦z≦1), and the layered structure is made of Ga
s
Al
t
In
1-s-t
N (where 0<s≦1, 0≦t<1, and 0<s+t≦1).
In one embodiment, the substrate, the first cladding layer, the surface protecting layer and the current blocking layer are of a first conductivity type, the second cladding layer is of a second conductivity type, and the layered structure further includes: a buffer layer of the first conductivity type formed on the substrate, and a contact layer of the second conductivity type formed on the internal current blocking layer of the first conductivity type.
In one embodiment, the substrate is non-conductive, the first cladding layer, the surface protecting layer and the internal current blocking layer are of a first conductivity type, the second cladding layer is of a second conductivity type, and the layered structure further includes: a first buffer layer and a second buffer layer which are formed on the substrate, the second buffer layer being of the first conductivity type; and a contact layer of the second conductivity type formed on the internal current blocking layer of the first conductivity type.
In one embodiment, the surface protecting layer is formed at a temperature in a range from about 400° C. to about 650° C.
According to another aspect of the present invention, a method for producing a gallium nitride group compound semiconductor light-emitting device, comprising the steps of: forming an N-type GaN buffer layer and an N-type Al
x
Ga
1-x
N cladding layer on an N-type substrate (where 0≦x<1); forming an In
y
Ga
1-y
N active layer on the N-type Al
x
Ga
1-x
N cladding layer (where 0≦y≦1; y≠0 for x=0); forming a P-type Al
x
Ga
1-x
N cladding layer (where 0≦x<1) and a P-type Al
x
Ga
1-x
N high impurity-concentration layer (where 0≦x<1) on the In
y
Ga
1-y
N active layer; forming an upper part of the P-type Al
x
Ga
1-x
N cladding layer and the P-type Al
x
Ga
1-x
N high impurity-concentration layer into a stripe-shaped projection; selectively forming an N-type Al
z
Ga
1-z
N surface protecting layer (where 0≦z≦1) and an N-type Al
w
Ga
1-w
N internal current blocking layer (where 0≦w≦1) on a part of a surface of the projection; and forming a P-type contact layer on the N-type Al
w
Ga
1-w
N internal current blocking layer, wherein the step of forming the N-type Al
z
Ga
1-z
N surface protecting layer is performed at a temperature in a first temperature range, the first temperature range being a range in which evaporation of Ga, N or impurity elements is prevented, is provided.
According to still another aspect of the present invention, a method for producing a gallium nitride group compound semiconductor light-emitting device, comprising the steps of: forming a P-type GaN buffer layer and a P-type Al
x
Ga
1-x
N cladding layer on a P-type substrate (where 0≦x<1); forming an In
y
Ga
1-y
N active layer on the P-type Al
x
Ga
1-x
N cladding layer (where 0≦y≦1; y≠0 for x=0); forming an N-type Al
x
Ga
1-x
N cladding layer (where 0≦x<1) and an N-type Al
x
Ga
1-x
N high impurity-concentr
Arroyo Teresa M.
Leung Quyen P.
Morrison & Foerster / LLP
Sharp Kabushiki Kaisha
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