Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With heterojunction
Reexamination Certificate
2002-02-19
2003-04-01
Whitehead, Jr., Carl (Department: 2813)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With heterojunction
C257S096000, C257S190000, C257S191000, C257S200000, C257S201000, C438S022000, C438S046000, C438S047000, C438S604000
Reexamination Certificate
active
06541799
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a Group-III nitride semiconductor light-emitting diode (LED) comprising an Si single crystal as a substrate. More specifically, the present invention relates to a high emission-intensity pn-heterojunction structure type Group-III nitride semiconductor light-emitting LED reduced in the absorption of emission attributable to a single crystal substrate, and also relates to a production method thereof.
BACKGROUND OF THE INVENTION
A silicon (Si) single crystal is conventionally known as a representative semiconductor substrate material having an electric conductivity advantageous for the input/output of a device driving power source and exhibiting cleavability useful for cutting into individual elements. Recently, techniques for fabricating a Group-III nitride semiconductor light-emitting diode (LED) using a silicon single crystal (silicon) as a substrate have been disclosed (see,
Electron. Lett.,
33(23), pp. 1986-1987 (1997)).
In the Group-III nitride semiconductor nitride light-emitting diode, a light-emitting part having a pn-double heterojunction structure composed of aluminum gallium nitride (Al
a
Ga
1−a
N, wherein 0≦a≦1) and gallium indium nitride (Ga
a
In
1−a
N, wherein 0≦a≦1) is provided (see,
Appl. Phys. Lett.,
72(4), pp. 415-417 (1998)).
The Si single crystal as a substrate has a lattice mismatch relationship with the Group-III nitride semiconductor constituting the light-emitting part. A large number of conventional techniques have been proposed to provide an intermediate layer between the single crystal substrate and the light-emitting part of LED to act as a buffer for the mismatch.
For example, a proposal has been made to provide an intermediate layer composed of aluminum nitride (AlN) for relieving the lattice mismatching and thereby obtaining a good quality light-emitting layer (see,
Appl. Phys.
, supra, and JP-A-10-242586 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)).
Also, a technique of providing boron phosphide (BP) as a buffer layer on a zinc-blend type single crystal substrate such as gallium phosphide (GaP) and silicon is known (see, JP-A-2-275682, JP-A-2-288371 and JP-A-2-288388).
Furthermore, a technique of providing a metal film such as titanium (Ti) as an intermediate layer on an Si single crystal substrate is also proposed (see, JP-A-2000-261033).
In addition, a technique of disposing a titanium nitride (TiN) layer or a nitride layer of cobalt (Co) or the like as an intermediate layer on an Si single crystal substrate having a crystal plane of {111} is also disclosed (see, JP-A-2000-286449).
On the other hand, the band gap of Si single crystal is about 1.1 electron volts (unit: eV) (see, Iwao Teramoto,
Handotai Device Gairon
(
Introduction of Semiconductor Device
), page 28, Baihukan (May, 30, 1995)). This band gap is as small as half or less as compared, for example, with the transition energy corresponding to light emission in the blue band. Because of this, in the LED fabricated using an Si single crystal as the substrate, the light emission at the short wavelength region radiated from the light-emitting part of a Group-III nitride semiconductor is disadvantageously absorbed by the Si crystal substrate. In other words, absorption of emitted light by Si single crystal substrate cannot be avoided when the Group-III nitride semiconductor LED uses a Si as a substrate material and therefore, a high brightness Group-III nitride semiconductor LED can be hardly obtained.
For increasing the emission intensity of a Group-III nitride semiconductor LED using a Si substrate, a technique of providing a Bragg reflection (DBR) structure layer for reflecting the emitted light toward the outside, between the Si substrate and the light-emitting part has been disclosed (see,
Mat. Res. Soc. Symp. Proc.
, Vol. 449 (1997), pp. 79-84). The DBR layer in conventional examples is composed of a periodic laminate structure where Al
a
Ga
1−a
N (0≦a≦1) thin layers different in the aluminum composition ratio (=a) are repeatedly superposed on one another. The reflectance of emitted light from the DBR layer can be improved by increasing the lamination period unit but the lamination operation becomes disadvantageously more cumbersome.
Although a large number of proposals have been heretofore made to eliminate the substrate of LED and thereby increase the light emission intensity, mere removal of the substrate part from LED inevitably impairs the mechanical strength of LED. Therefore, a reasonable countermeasure is demanded. Under these circumstances, development of a method for obtaining a high emission intensity Group-III nitride semiconductor light-emitting LED having a sufficiently high mechanical strength by simpler and easier technical means has been demanded.
SUMMARY OF THE INVENTION
An object of the present invention is to develop a Group-III nitride semiconductor LED using an Si single crystal substrate, which is a high brightness Group-III nitride semiconductor LED obtained by technical means of eliminating the Si single crystal substrate from LED without losing the mechanical strength of LED and thereby reducing the absorption of emitted light attributable to the Si substrate.
More specifically, the present invention has overcome the above-described problems by developing the following embodiments:
[1] a Group-III nitride semiconductor light-emitting diode comprising an electrically conducting silicon (Si) single crystal substrate having on an upper surface thereof at least a light-emitting part having a pn-heterojunction structure composed of a Group-III nitride semiconductor, which light-emitting part is stacked via an intermediate layer composed of a metal or a semiconductor, the single crystal substrate having a back surface electrode on a back surface thereof, a surface electrode on an upper surface of the light-emitting part and a perforated part formed by eliminating the Si single crystal substrate in a region exclusive of the back surface electrode on the back surface of the single crystal substrate;
[2] the Group-III nitride semiconductor light-emitting diode as described in [1] above, wherein the back surface electrode on the silicon single crystal substrate comprises a continuous metal coating electrode;
[3] the Group-III nitride semiconductor light-emitting diode as described in [1] or [2] above, wherein the back surface electrode on the silicon single crystal substrate comprises a continuous metal coating electrode in an outer circumference of the perforated part;
[4] the Group-III nitride semiconductor light-emitting diode as described in [1] or [3] above, wherein the bottom surface of the perforated part is the above-described intermediate layer;
[5] the Group-III nitride semiconductor light-emitting diode as described in [4] above, wherein the intermediate layer comprises a Group III-V compound semiconductor film containing phosphorus (P);
[6] the Group-III nitride silicon semiconductor light-emitting diode as described in [4] or [5] above, wherein the intermediate layer comprises MN
1−X
P
X
wherein M represents a Group-III element other than boron, and X is in the range of 0<X≦1;
[7] the Group-III nitride semiconductor light-emitting diode as described in [4] or [5] above, wherein the intermediate layer comprises B
X
M
1−X
P wherein M represents a Group-III element other than boron, and X is in the range of 0<X≦1;
[8] the Group-III nitride semiconductor light-emitting diode as described in [7] above, wherein the intermediate layer has a concentration gradient of a Group-III constituent element or Group-V constituent element;
[9] a method for manufacturing a Group-III nitride semiconductor light-emitting diode, which comprises providing an intermediate layer having a low-tempe
Hogans David L.
Jr. Carl Whitehead
Showa Denko K.K.
Sughrue & Mion, PLLC
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