Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal
Reexamination Certificate
1998-07-30
2003-04-29
Smith, Matthew (Department: 2825)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
C438S022000, C257S010000, C257S011000, C257S012000, C257S013000, C257S014000, C257S079000, C257S080000, C257S081000, C257S082000, C257S083000, C257S084000, C257S085000, C257S086000
Reexamination Certificate
active
06555403
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor laser, a semiconductor light emitting device, andmethods of manufacturing the same and, more particularly, a semiconductor laser which has a feature in configuration to reduce a threshold current density in a semiconductor laser using a nitride compound semiconductor, and a method of manufacturing the same.
2. Description of the Prior Art
In the prior art, a short wavelength semiconductor laser has been employed as a light source of an optical disk, a DVD (digital versatil disk) drive, etc. Since a recording density of the optical disk is in inverse proportion to square of a wavelength of a laser beam, a semiconductor laser which is able to emit a laser beam of shorter wavelength is requested. A currently available semiconductor laser which is able to emit a shortest wavelength is a red-light emitting semiconductor laser which has a wavelength of about 630 to 650 nm and is incorporated into the DVD drive put on sale in last year.
However, in order to enhance the recording density higher in a photo memory device, a shorter wavelength of an output light is needed. By way of example, a blue-light semiconductor laser which has a wavelength or around 400 nm is indispensable for recording moving pictures on the optical disk for two hours. Hence, in recent years, the short wavelength emitting semiconductor laser which has a wavelength in a blue light emitting range has been developed actively as a next generation optical disk light source.
As material for the blue-light emitting semiconductor laser mentioned above, ZnSe (Zinc selen) system in group II-VI compound semiconductor and GaN system in group III-V compound semiconductor have been studied. Since the ZnSe system can substantially lattice-match with Gays which has attained great actual results as a high quality substrate, it has been considered for a long time that the ZnSe system is more advantageous than the GaN system. Therefore, most of the research scholars in the world have been engaged with study of the ZnSe system and thus the ZnSe system has gone ahead in the field of semiconductor laser study.
As for the ZnSe system, room-temperature continuous-wave oscillation (CW oscillation) due to the injection excitation has already been reported. However, since essentially the ZnSe system is material which is ready to deteriorate, its reliability becomes an issue and therefore the ZnSe system has not yet come up to practical implementation.
In contrast, in the case of the GaN system, after the announcement of the GaN (gallium nitride) high luminance LED being manufactured by Nichia Chemical Co., Ltd. at the end of 1993 which acts as the boundary, the GaN being excellent in environment resistance such as reliability which is the bottleneck of the ZnSe system has been looked at again and the number of the research scholars in the world has been risen largely.
Then, study of the GaN system has advanced rapidly since the success of pulse laser oscillation has been reported similarly by Nichia Chemical Co., Ltd. early in December, 1995. After oscillation duration of 35 hours has been reported in the room-temperature continuous-wave oscillation (CW oscillation), currently the oscillation duration of 10,000 hours has been presumed in an accelerated test.
Next, the short wavelength light emitting semiconductor device in the prior art will be explained with reference to
FIGS. 1
,
2
and
FIG. 3
hereinbelow.
FIG. 1
is a schematic sectional view, taken along its optical axis, showing the short wavelength emitting semiconductor laser in the prior art, and
FIG. 2
is a schematic sectional view showing a short wavelength light emitting diode in the prior art.
FIG. 3
is a schematic sectional view showing the short wavelength emitting semiconductor laser having a different buffer layer structure in the prior art.
The semicnductor laser is formed as follows.
First, as shown in
FIG. 1
, a GaN buffer layer
812
, an n-type GaN buffer layer
813
, an n-type In
0.1
Ga
0.9
N (indium gallium nitride) layer
814
, an n-type Al
0.15
Ga
0.85
N (aluminum gallium nitride) cladding layer
815
, an n-type GaN optical guiding layer
816
, an InGaN MQW (multi-quantum well) active layer
817
, a p-type Al
0.2
Ga
0.8
N layer
818
, a p-type GaN optical guiding layer
819
, a p-type Al
0.15
Ga
0.85
N cladding layer
820
, and a p-type GaN contact layer
821
are epitaxially grown in sequence on a sapphire substrate
811
having a (0001) plane as a principal plane, by an MOVPE (metal organic vapor-phase epitaxy) method.
Then, a part of the n-type GaN buffer layer
813
is exposed by means of dry etching, then an n-side electrode
822
made of Ti/Au (titanium/gold) is formed on an exposed surface and also a p-side electrode
823
made of Ni/Au (nickel/gold) is formed on the p-type GaN contact layer
821
, Then, a pair of parallel and surfaces are formed by applying dry etching. A pulse laser oscillation can be achieved successfully by adopting the end surfaces as resonator faces. If necessary, refer S. Nakamura et al.; Japanese Journal of Applied Physics, vol.35, p.L74, 1996).
In
FIG. 2
, in the case of the light emitting diode, the GaN buffer layer
812
, an n-type GaN layer
824
, an n-type or p-type In
0.15
Ga
0.85
N active layer
825
, and a p-type GaN layer
826
are epitaxially grown on the sapphire substrate
811
by the MOVPE method.
In this case, in order to obtain a practical luminescence brightness as the light emitting diode which can be operated by virtue of low injection, a Si (silicon) concentration or Zn (zinc) concentration in the In
0.15
Ga
0.85
N active layer
825
must be set to 1×10
17
to 1×10
21
atoms/cm
3
and also a thickness of the In
0.15
Ga
0.85
N active layer
825
must be set to 1 to 500 nm, more preferably 10 to 100 nm If necessary, refer Patent application Publication (KOKAI) Hei 6-260682 and Patent application Publication (KOKAI) Hei 6-260683.
FIG. 3
is a sectional view, taken along its optical axis, showing another short wavelength semiconductor laser in the prior art. First, a GaN buffer layer
832
, an n-type GaN intermediate layer
833
, an n-type Al
0.09
Ga
0.91
N cladding layer
834
, an n-type GaN optical guiding layer
835
, an MQW active layer
836
, a p-type Al
0.18
Ga
0.82
N overflow preventing layer
837
, a p-type GaN optical guiding layer
836
, a p-type Al
0.09
Ga
0.91
N cladding layer
839
, and a p-type GaN contact layer
840
are epitaxially grown in sequence on a sapphire substrate
831
having the (0001) plane as the principal plane, by the MOVPE method.
Then, like the case in
FIG. 1
, the p-type GaN contact layer
840
and the p-type Al
0.09
Ga
0.91
N cladding layer
839
are mesa-etched by virtue of dry etching, then a part of the n-type GaN intermediate layer
833
is exposed by means of dry etching, then an n-side electrode
841
made of Ti/Au is provided on an exposed surface of the n-type GaN intermediate layer
833
and also a p-side electrode
843
made of Ni/Au is provided on the p-type G&N contact layer
840
via a stripe-like opening or a SiO
2
(silicon oxidation) film
842
. Then, a pair of parallel end surfaces acting as resonator faces respectively are formed by applying dry etching.
In addition, it has been proposed that the overflow preventing layer, i.e., the carrier stopper layer is provided to the n-side layer side. If necessary, refer Patent application Publication (KOKAI) Hei 10-56236. In this case, an n-type Si doped Al
0.15
Ga
0.85
N layer as a hole stopper layer, whose n-type impurity concentration is 1×10
19
atoms/cm
3
, and a p-type Mg doped Al
0.15
Ga
0.85
N layer as an electron stopper layer, whose p-type impurity concentration is 5×10
19
atoms/cm
3
, are provided between the active layers and the optical guiding layers respectively. At that time, the growth temperature is 1100° C. which is a usual temperature used to grow GaN or ALGWN.
However, in the case of the short wavelength semiconductor laser in the prior art, there has been such a prob
Domen Kay
Kubota Shin'ichi
Kuramata Akito
Soejima Reiko
Armstrong Westerman & Hattori, LLP
Lee Granvill D
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