Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With particular semiconductor material
Reexamination Certificate
2002-09-09
2003-10-21
Meier, Stephen D. (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With particular semiconductor material
C257S079000
Reexamination Certificate
active
06635905
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gallium nitride based compound semiconductor device, and more particularly to a gallium nitride based compound semiconductor light emitting device with a reduced operating current and a reduced device resistance, for emitting a laser beam with a basic transverse mode and a generally circular shape of beam section.
All of patents, patent applications, patent publications, scientific articles and the like, which will hereinafter be cited or identified in the present application, will, hereby, be incorporated by references in their entirety in order to describe more fully the state of the art, to which the present invention pertains.
2. Description of the Related Art
The requirement for development of a gallium nitride based compound semiconductor laser with a reduced operating current and a reduced device resistance, for emitting a laser beam with a basic transverse mode and a generally circular shape of beam section has been on the increase. The semiconductor laser of this type has a high utilization efficiency of laser beam in applications to laser disks and laser printers. The high utilization efficiency of laser beam may realize a desired high laser power on a recording face and a desired high recording speed. The semiconductor laser of this type does not need an additional optical element for shaping a generally circular beam section. The absence of such additional optical element may realize a scaling down of the device and a reduction of the cost.
A gallium nitride based compound semiconductor laser, which emits a laser beam with a wavelength near 400 nanometers, has a focusing spot area which is smaller by three times than that of a red-color semiconductor laser, which emits a red-color laser beam with a wavelength near 650 nanometers. The smaller focusing spot area is advantageous in applying the laser to high density recording optical disks and laser printers.
A conventional gallium nitride based compound semiconductor laser will be described hereinafter with reference to the drawings.
FIG. 1
is a fragmentary cross sectional elevation view of an example of the conventional gallium nitride based compound semiconductor laser. This laser is disclosed by S. Nakamura et al. in Applied Physics Letters, vol. 72, 1998, pp. 2014-2016. The conventional gallium nitride based compound semiconductor laser is formed over a GaN substrate
101
which has a thickness of 80 micrometers. An n-type GaN contact layer
102
with a thickness of 3 micrometers is provided over the GaN substrate
101
. An n-type In
0.1
Ga
0.9
N layer
103
with a thickness of 0.1 micrometer is provided over the n-type GaN contact layer
102
.
An n-type super-lattice cladding layer
104
with a total thickness of 1.2 micrometers is provided over the n-type In
0.1
Ga
0.9
N layer
103
. The super-lattice comprises 240 periods of alternating laminations of an n-type GaN layer with a thickness of 2.5 nanometers and an n-type Al
0.14
Ga
0.86
N layer with a thickness of 2.5 nanometers. An n-type GaN optical guide layer
105
with a thickness of 0.1 micrometer is provided over the n-type super-lattice cladding layer
104
. An undoped multiple quantum well active layer
106
is provided over the n-type GaN optical guide layer
105
. The multiple quantum well active layer
106
comprises 4 periods of alternating laminations of an undoped In
0.15
Ga
0.85
N quantum well layer with a thickness of 2 nanometers and an undoped In
0.02
Ga
0.98
N barrier layer with a thickness of 5 nanometers.
A p-type Al
0.2
Ga
0.8
N layer
107
with a thickness of 20 nanometers is provided over the undoped multiple quantum well active layer
106
. A p-type GaN optical guide layer
108
with a thickness of 0.1 micrometer is provided over the p-type Al
0.2
Ga
0.8
N layer
107
. A p-type super-lattice cladding layer
109
with a total thickness of 0.6 micrometers is provided over the p-type GaN optical guide layer
108
. The super-lattice comprises 120 periods of alternating laminations of an n-type GaN layer with a thickness of 2.5 nanometers and an n-type Al
0.14
Ga
0.86
N layer with a thickness of 2.5 nanometers. A p-type GaN contact layer
110
with a thickness of 0.05 micrometers is provided over the p-type super-lattice cladding layer
109
.
The p-type super-lattice cladding layer
109
has a ridged structure
113
with a stripe-shape top surface having a width of 3 micrometers. The ridged structure
113
is selectively provided over the p-type GaN optical guide layer
108
. An SiO
2
insulating layer
114
is provided on sloped side faces of the ridged structure
113
and on the top surface of the p-type GaN optical guide layer
108
. The SiO
2
insulating layer
114
has an opening over the top of the stripe-shape top surface of the ridged structure of the p-type super-lattice cladding layer
109
. The p-type GaN contact layer
110
is provided on the top of the ridged structure of the p-type super-lattice cladding layer
109
. The SiO
2
insulating layer
114
causes a current confinement into the p-type super-lattice cladding layer
109
.
The lamination structure of the n-type In
0.1
Ga
0.9
N layer
103
, the n-type super-lattice cladding layer
104
, the n-type GaN optical guide layer
105
, the undoped multiple quantum well active layer
106
, the p-type Al
0.2
Ga
0.8
N layer
107
and the p-type GaN optical guide layer
108
has a step-like side wall
115
which is formed by a selective etching to the lamination structure and a part of an upper region of the n-type GaN contact layer
102
. The n-type GaN contact layer
102
has an etched terrace.
A p-electrode
111
extends over the p-type GaN contact layer
110
and the insulating layer
114
. An n-electrode
112
is provided on the etched terrace of the n-type GaN contact layer
102
. Since the GaN substrate
101
has a high resistivity, the n-electrode
112
is provided in contact with the n-type GaN contact layer
102
.
This laser of
FIG. 1
emits a laser beam with a wavelength of 393 nanometers, and has an emission threshold current lower than 110 mA of the conventional one. The GaN crystal substrate is lower in crystal defect or dislocation than a sapphire substrate. The low crystal defect or dislocation of the substrate may realize a longer life-time of the laser. A beam shape in a far field of view has an elliptic shape, wherein the emission laser beam has a horizontal radiation angle of 8 degrees in full width at half maximum and a vertical radiation angle of 31 degrees in full width at half maximum. An aspect ratio is an indication of the elliptic shape. The aspect ratio is given by a ratio of the vertical radiation angle to the horizontal radiation angle. The aspect ratio of this laser is about 3.9. This means that the beam shape is a slender elliptic shape.
Another conventional gallium nitride based compound semiconductor laser will be described hereinafter with reference to the drawings.
FIG. 2
is a fragmentary cross sectional elevation view of an example of the other conventional gallium nitride based compound semiconductor laser. This laser is disclosed by S. Nakamura et al. in Applied Physics Letters, vol. 39, 2000, pp. L647-L650. The conventional gallium nitride based compound semiconductor laser is formed over a GaN substrate
201
which has a thickness of 150 micrometers. An n-type Al
0.05
Ga
0.95
N contact layer
202
with a thickness of 5 micrometers is provided over the GaN substrate
201
. An n-type In
0.1
Ga
0.9
N layer
203
with a thickness of 0.1 micrometer is provided over the n-type Al
0.05
Ga
0.95
N contact layer
202
.
An n-type super-lattice cladding layer
204
with a total thickness of 0.9 micrometers is provided over the n-type Al
0.05
Ga
0.09
N contact layer
202
. The super-lattice comprises 180 periods of alternating laminations of an n-type GaN layer with a thickness of 2.5 nanometers and an n-type Al
0.1
Ga
0.9
N layer with a thickness of 2.5 nanometers. An n-type GaN optical guide layer
205
with a thickness of 0.15 micrometer is provided over the n
Kuramoto Masaru
Nido Masaaki
Yamaguchi Atsushi
Meier Stephen D.
NEC Corporation
Young & Thompson
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