Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With particular dopant concentration or concentration profile
Reexamination Certificate
2001-06-22
2004-09-07
Flynn, Nathan J. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With particular dopant concentration or concentration profile
C257S079000, C257S094000, C257S095000, C257S096000, C257S102000, C257S103000
Reexamination Certificate
active
06787814
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a group-III nitride semiconductor light-emitting device comprising a substrate such as silicon (Si) having on the surface thereof a light-emitting part structure containing a gallium nitride phosphide (GaN
1−X
P
X
, wherein 0<X<1) single crystal layer provided via a boron phosphide (BP)-based buffer layer.
BACKGROUND OF THE INVENTION
A group-III nitride semiconductor light-emitting device that emits light in the blue or green band is composed of a multilayer structure where a gallium nitride (GaN) crystal layer as one constituent element is disposed, for example, on a sapphire (&agr;-Al
2
O
3
) single crystal substrate using a growing technique, such as metal organic chemical vapor deposition (MOCVD) method. The multilayer structure has a light-emitting part structure undertaking the function of emitting light. Conventionally, the light-emitting part structure in general takes a pn junction-type hetero structure constructed by a p-type or n-type clad layer consisting of a light-emitting layer formed of gallium indium nitride (Ga
y
In
1-Y
N, wherein 0<Y≦1) and an aluminum gallium indium nitride (AlGaInN)-based crystal layer.
FIG. 5
is a schematic sectional view showing an example of the construction of a conventional multilayer structure light-emitting device (LED)
100
having a pn junction-type double hetero (DH) junction light-emitting part structure
42
comprising an AlGaInN-base crystal layer. In a conventional multilayer structure, the light-emitting part structure
42
is composed of, for example, a lower clad layer
103
comprising an n-type aluminum gallium nitride (Al
Z
Ga
1−Z
N, wherein 0≦Z≦1) crystal layer, a light-emitting layer
104
comprising an n-type gallium indium nitride (Ga
Y
In
1-Y
N) and an upper clad layer
105
comprising a p-type aluminum gallium nitride (Al
Z
Ga
1−Z
N, wherein 0≦Z≦1) (see, JP-A-6-260682 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)). The functional layers
103
to
105
constituting the light-emitting part structure
42
each is usually deposited with an intervention of a buffer layer formed at a temperature lower than the temperature at the formation of those functional layers, so-called a low-temperature buffer layer
102
(see, JP-A-4-297023). Furthermore, in a multilayer structure comprising a sapphire substrate
101
having provided thereon a group-III nitride semiconductor crystal layer, the low-temperature buffer layer
102
is usually composed of aluminum gallium nitride (Al
Z
Ga
1−Z
N, wherein 0≦Z≦1) (see, JP-A-6-151962).
The low-temperature buffer layer
102
is provided mainly for the purpose of reducing the lattice mismatch between the sapphire substrate
101
and the lower clad layer
103
composed of Al
Z
Ga
1−Z
N crystal, thereby obtaining a good group-III nitride single crystal layer reduced in the density of crystal defects such as dislocation. Particularly, in a known conventional example, the low-temperature buffer layer
102
is composed of gallium nitride (GaN), the lower clad layer
103
is composed of a GaN layer formed at a high temperature in excess of the temperature for the formation of the low-temperature buffer layer
102
, and the light-emitting layer
104
is composed of a gallium indium nitride mixed crystal phase (see, JP-A-6-216409).
Furthermore, in the conventional light-emitting device shown in
FIG. 5
, the substrate
101
is an insulating sapphire and therefore, a part of the lower clad layer
103
must be removed to provide an n-type ohmic electrode
107
. A p-type ohmic electrode
106
is provided on the electrically conducting upper clad layer
105
.
However, the mismatch between the sapphire substrate and the GaN layer constituting the low-temperature buffer layer is as high as about 13.8% (see, Nippon Kessho Seicho Gakkai Shi (Journal of Japan Crystal Growth Society), Vol. 15, Nos. 3 & 4, pp. 74-82 (Jan. 25, 1989)) and therefore, a continuous low-temperature buffer layer cannot be stably obtained at present. In the discontinuous portion partially present in the low-temperature buffer layer due to the lacking of film continuity, namely, in the region where the sapphire substrate surface is exposed, hexagonal GaN predominantly grows in the c-axis direction thereof. As a result, dislocation is generated starting from the coalescence of GaN columnar crystals, propagates to the GaInN light-emitting layer via the upper GaN layer and disadvantageously deteriorates the crystal quality of the light-emitting layer. In other words, according to the above-described conventional multilayer structure constructed by stacking a GaInN light-emitting layer on a GaN low-temperature buffer layer via a GaN layer, a good GaInN-type light-emitting layer film cannot be formed due to the propagation of crystal defects such as dislocation attributable to the discontinuity of the low-temperature buffer layer. Therefore, stable formation of a light-emitting part structure comprising a group-III nitride single crystal layer having excellent operation reliability or ensuring long device life cannot be attained particularly in the case of a laser diode (LD).
The present invention has been made by taking into account these problems in conventional techniques, and an object of the present invention is to provide a buffer layer having continuity capable of allowing homogeneous coating on the substrate surface and preventing generation of dislocations despite a large mismatch with the substrate crystal. Another object of the present invention includes providing a construction of a group-III nitride single crystal layer structure deposited on the above-described buffer layer, which is reduced in the density of crystal defects such as dislocation and favored with excellent crystallinity.
SUMMARY OF THE INVENTION
More specifically, the group-III nitride semiconductor light-emitting device of the present invention is a group-III nitride semiconductor light-emitting device comprising a single crystal substrate having thereon a light-emitting part structure containing a gallium nitride phosphide (GaN
1−X
P
X
, wherein 0<X<1) single crystal layer provided via a boron phosphide (BP)-based buffer layer.
By using the boron phosphide-based buffer layer, the lattice mismatch of crystals between the substrate and the gallium nitride phosphide light-emitting part structure can be eliminated and a gallium nitride phosphide light-emitting part structure having excellent crystallinity can be formed. As a result, a high-emission intensity light-emitting device can be advantageously obtained.
In the group-III nitride semiconductor light-emitting device of the present invention, the boron phosphide-based buffer layer is amorphous.
The BP-based buffer layer is rendered amorphous by growing it at a low temperature, which has an effect of allowing the buffer layer to cope with a substrate having a lattice constant over a wide range.
In the group-III nitride semiconductor light-emitting device of the present invention, the BP-based buffer layer may be composed of an amorphous and crystalline multilayer structure.
By providing an amorphous BP-based buffer layer in the vicinity of an interface with the substrate and providing a crystalline BP-based buffer layer in the vicinity of the light-emitting part structure thereon, a gallium nitride phosphide light-emitting part structure having higher crystallinity can be advantageously obtained with ease.
In the group-III nitride semiconductor light-emitting device of the present invention, the light-emitting part structure may be a single hetero-junction structure containing a gallium nitride phosphide single crystal layer.
The light-emitting part can have good crystallinity and therefore, a high-emission intensity light-emitting device can be obtained even with a simple light-emitting part structure.
In the group-III nitride semiconductor light-emitting device of the present invention, the light-emitting part structure may be a doubl
Flynn Nathan J.
Mondt Johannes P.
Showa Denko Kabushiki Kaisha
LandOfFree
Group-III nitride semiconductor light-emitting device and... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Group-III nitride semiconductor light-emitting device and..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Group-III nitride semiconductor light-emitting device and... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3227914