Active solid-state devices (e.g. – transistors – solid-state diode – Incoherent light emitter structure – With heterojunction
Reexamination Certificate
2002-06-05
2004-08-03
Crane, Sara (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Incoherent light emitter structure
With heterojunction
C257S103000, C257S794000
Reexamination Certificate
active
06770914
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a III nitride semiconductor substrate for Epitaxial Lateral Overgrowth (simply referred to as ‘ELO’, hereinafter), particularly a III nitride semiconductor substrate for ELO preferably usable as a substrate constituting a semiconductor light-emitting element such as a light-emitting diode, or a semiconductor element such as a high frequency or high output electronic device.
(2) Related Art Statement
III nitride films are employed as semiconductor films constituting a semiconductor light-emitting element such as a light-emitting diode, and recently, have caught a lot of attention as semiconductor flints constituting semiconductor elements such as high frequency electronic devices used in e.g. cellular phones.
Such III nitride films are usually formed by MOCVD methods. Concretely, a substrate on which III nitride films are formed is set onto a susceptor installed in a given reactor, and then, heated to 1000° C. or over with a heater provided in or out of the susceptor, Thereafter, raw material gases are introduced with a carrier gas into the reactor and supplied onto the substrate
On the substrate, the raw material gases arc dissolved through thermochemical reaction into constituent elements, which are reacted to deposit and form a desired III nitride film on the substrate. The film is required to be low in its dislocation density, so that a semiconductor element constructed by the film attains designed properties.
However, since the melting points of III nitride materials are relatively high, it has been difficult to grow bulk single crystals made of the above III nitride materials. Therefore, there had been no means except that the nitride films are formed by heteroepitaxial growth on a different kind of single crystal substrate such as a sapphire single crystal substrate
Actually, since the lattice constant of a GaN-based III nitride film largely differs from that of a sapphire single crystal substrate, misfit dislocations are created depending on the difference in the lattice constant, at the boundary between the GaN-based III nitride film and the sapphire single crystal substrate. Thereafter, misfit dislocations propagate into the GaN-based III nitride film, increasing the amount of dislocations in the GaN-based III nitride film. Such dislocations due to lattice misfit can be reduced to a certain extent by inserting a buffer layer grown at low temperature between the GaN-based Ill nitride film and the sapphire single crystal substrate.
However, in case of fabricating semiconductor elements required for a high output such as a laser diode or a light-emitting diode with high brightness, a light-detecting device is required for a low dark current, and an electronic device required for a high output at high frequency. The above GaN-based III nitride film was unable to attain desired performances to meet designed properties owing to its high dislocation density.
From the above point of view, an ELO technology has been developed, and a substrate using ELO technology has been developed.
FIG. 1
shows a structure of a conventional III nitride semiconductor substrate for ELO.
FIG. 2
shows that a GaN-based III nitride film is formed on the III nitride semiconductor substrate for ELO shown in
FIG. 1
, by using an ELO technology.
The III nitride semiconductor substrate
5
for ELO shown in
FIG. 1
is constructed by sequentially forming the buffer layer
2
made of e.g. GaN grown at low temperature, the underlayer
3
made of e.g. GaN, and the patterned layer
4
made of e.g. SiO
2
, on the base
1
made of e.g. sapphire single crystal.
As shown in
FIG. 2
, if the GaN-based III nitride film
6
is formed on the III nitride semiconductor substrate
5
for ELO, dislocations penetrating from the underlayer
3
to the GaN-based III nitride film
6
propagate in the upper direction after laterally propagating as surrounding the pattern
4
as shown by the arrow X
1
, and propagate in the upper direction only as shown by the arrow X
2
.
Consequently, the amount of dislocations in the region A of the GaN-based III nitride film
6
above the pattern
4
are reduced. Therefore, the above semiconductor element has good properties because of its constituents' high crystal quality, utilizing the region A as predetermined constituents of the semiconductor element.
FIG. 3
shows a structure of another example of a conventional III nitride semiconductor substrate for ELO, and
FIG. 4
shows that a GaN-based III nitride film is formed by an ELO technology on the III nitride semiconductor substrate for ELO shown in FIG.
3
.
The III nitride semiconductor substrate
15
for ELO shown in
FIG. 3
is constructed by sequentially forming the buffer layer
12
made of e.g. GaN formed at low temperature, and the underlayer
13
made of e.g. GaN having a concave-convex surface, on the base
11
made of e.g. sapphire single crystal.
As shown in
FIG. 4
, if GaN-based III nitride film
16
is formed on the HII nitride semiconductor substrate
15
for ELO, misfit dislocations created between the underlayer
13
and the GaN-based III nitride film
16
propagate in the upper direction after laterally propagating from the convex part
13
A to the concave part
13
B in the under layer
13
as shown by the arrow Y
1
, and propagate in the upper direction only as shown by the arrow Y
2
.
Consequently, the amount of dislocations in the region B above the concave part
13
B in the GaN-based III nitride film
16
are reduced. Therefore, the above semiconductor element has good properties because of its constituents' high crystal quality, utilizing the domain B as predetermined constituents of the semiconductor element.
In case of growing the GaN-based III nitride film by means of ELO technology, since there is a region in which dislocations extend above as shown in
FIGS. 2 and 4
, an inconvenience has been that there is a limitation as to the region usable as a semiconductor element. As a result, if a laser diode, for example, is constructed by the above GaN-based II nitride film, luminous efficiency has been degraded owing to a lot of useless regions not usable as a semiconductor element. causing its yield to lower in photolithography processes.
Furthermore, if a light-emitting diode, for example, is constructed by the above GaN-based III nitride film, there had been an inconvenience that a lot of difference of light-emitting strength exists in the element, causing its light-emitting efficiency to decrease.
Furthermore, in case of utilizing the above GaN-based III nitride film as a substrate for a semiconductor element, it is necessary to form the GaN-based III nitride film comparably thickly, for example, 100 &mgr;m and more. However, in case of forming the GaN-based III nitride films by utilizing the III nitride semiconductor substrat
15
for ELO shown in
FIGS. 1
or
3
, there has been an inconvenience That the surface roughness of the GaN-based III nitride films gets worse considerably, as its thickness becomes larger.
Moreover, in case that a semiconductor element is fabricated by forming a predetermined GaN-based III nitride film on the above III nitride films used as a substrate, the crystal quality of the above GaN-based III nitride film formed on a GaN-based III nitride film semiconductor substrate is deteriorated because of the surface roughness of the GaN-based III nitride film semiconductor substrate. Accordingly, it has been unable to provide desired properties for the above semiconductor element, without carrying out polish processing.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a III nitride film semiconductor substrate for ELO, to form a III nitride film having controlled surface roughness not depending on its thickness, as well as enhancing its use efficiency by controlling penetrating dislocations.
In order to accomplish the above object, the present invention relates to a III nitride semiconductor substrate for ELO, characterized in being provided with a predetermined
Asai Keiichiro
Shibata Tomohiko
Sumiya Shigeaki
Tanaka Mitsuhiro
Burr & Brown
Crane Sara
NGK Insulators Ltd.
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