Active solid-state devices (e.g. – transistors – solid-state diode – Thin active physical layer which is – Heterojunction
Reexamination Certificate
1999-01-20
2001-01-23
Jackson, Jr., Jerome (Department: 2815)
Active solid-state devices (e.g., transistors, solid-state diode
Thin active physical layer which is
Heterojunction
C257S024000, C257S076000, C257S192000, C257S194000, C257S201000, C257S610000, C257S612000, C257S615000
Reexamination Certificate
active
06177685
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a nitride-type III-V group compound semiconductor device, and in particular, to a semiconductor device using two-dimensional electron gas which has outstanding operational characteristics at high output, high frequency, and high temperature.
2. Description of the Related Art
Semiconductor devices using two-dimensional electron gas include a hetero-structure field-effect transistor (HFET), a high-electron-mobility transistor (HEMT), and a modulation-doped field effect transistor (MODFET). As such semiconductor devices using two-dimensional electron gas, a device using GaAs-type materials is under development.
As shown in
FIG. 8
, a conventional GaAs-type HFET generally includes, on a semi-insulating (SI-) GaAs substrate
101
, an undoped GaAs buffer layer
102
(thickness: 1 &mgr;m and carrier concentration: 3×10
16
cm
−3
), an undoped AlGaAs spacer layer
103
(thickness: 10 nm and carrier concentration: 1×10
17
cm
−3
), an n-type AlGaAs donor layer
104
(thickness: 20 nm and carrier concentration: 1×10
18
cm
−3
), and an n-type GaAs cap layer
105
(thickness: 10 nm and carrier concentration: 3×10
18
cm
−3
). Reference numerals
106
and
107
in
FIG. 8
denote a gate electrode and source/drain electrodes, respectively.
It should be noted that in the drawings, the term “2DEG” means “2-Dimensional Electron Gas” which is generated at the interface between a barrier and a channel when a hetero junction is formed.
Moreover,
FIG. 9
shows a structure of a conventional HFET using a nitride-type III-V group compound semiconductor (U.S. Pat. No. 5,192,987). The illustrated HFET using a nitride-type III-V group compound semiconductor has substantially the same structure as that of the GaAs-type HFET. Specifically, as shown in
FIG. 9
, the illustrated HFET using a nitride-type III-V group compound semiconductor includes, on an insulating substrate
201
(e.g., a sapphire substrate), an AlN low-temperature grown buffer layer
202
(thickness: 20 nm), a GaN buffer layer
203
(thickness: 2 &mgr;m and carrier concentration of 8×10
16
cm
−3
), an AlGaN donor layer
204
(thickness of 20 nm and carrier concentration of 1×10
18
cm
−3
), a gate electrode
205
, and source/drain electrodes
206
, and uses GaN as a channel material.
FIG. 10
shows a reverse structure HFET (Electronics Lett., Vol. 31, No. 22, (1995) pp. 1951-1952). As shown in
FIG. 10
, the reverse structure HFET includes, on an insulating substrate
301
made of sapphire and the like, an AlN low-temperature grown buffer layer
302
(thickness: 20 nm), a GaN buffer layer
303
(thickness: 3 &mgr;m), an AlN barrier layer
304
(thickness: 3 nm), and a GaN channel layer
305
(thickness: 100 nm). Reference numerals
306
and
307
in
FIG. 10
denote a gate electrode and source/drain electrodes, respectively.
An electron mobility of GaN, which is conventionally used as a constituting material of a channel layer, is about 200 cm
2
/Vs when its carrier concentration is about 1×10
18
cm
−3
and about 400 cm
2
/Vs when its carrier concentration is about 1×10
17
cm
−3
. This electron mobility is about one order of magnitude greater than that of other wide-band gap materials such as SiC, but about one order of magnitude smaller than that of GaAs used in a GaAs-type HFET.
In the case of the GaAs-type HFET, as described in Japanese Laid-Open Publication No. 63-161678, an InGaAs mixed crystal which has a larger mobility as compared with GaAs can be inserted to an interface of AlGaAs and GaAs as a channel material. Thus, it was considered that the similar method (i.e., insertion of InGaN) would be available for a nitride-type semiconductor device. In contrast to such expectation, however, in the case of the nitride-type III-V group compound semiconductor device, satisfactory crystallinity and/or flatness can not be obtained in the inserted InGaN mixed crystal, so that an electron mobility does not always become larger. Thus, the effect obtainable by an InGaAs channel layer in the GaAs-type HFET cannot be expected by the insertion of InGaN crystal.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, a nitride-type III-V group compound semiconductor device includes a substrate and a layered structure including at least a channel layer using two-dimensional electron gas formed over a substrate. The channel layer contains InN.
For example, the channel layer may be a single layer formed of InN, and has a thickness of about 1000 nm or less. Alternatively, the channel layer may have an InN/GaN multi-layered structure. As a further alternative, the channel layer may have an InN/AlN multi-layered structure.
In one embodiment of the invention, the GaN layer or the AlN layer in the multi-layered structure of the channel layer is modulation-doped.
In one embodiment of the invention, each layer included in the InN/GaN or InN/AlN multi-layered structure of the channel layer is a thin layer including a few mono-layers of InN/GaN or InN/AlN in which a mini-band is formed.
In one embodiment of the invention, the substrate is a conductive substrate, and the layered structure includes a buffer layer formed of a nitride-type semiconductor on the conductive substrate, and at least one element selected from the group consisting of Cr, Ti, Fe, Au, V and Nb is added to the buffer layer.
In one embodiment of the invention, the buffer layer includes an AlN layer.
In one embodiment of the invention, the substrate is formed of V-added SiC.
Thus, the invention described herein makes possible the advantage of providing a nitride-type III-V group compound semiconductor which has a large electron mobility in a channel.
This and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.
REFERENCES:
patent: 5192987 (1993-03-01), Khan et al.
patent: 5611955 (1997-03-01), Barrett et al.
patent: 5831277 (1998-11-01), Razeghi
patent: 5847414 (1998-12-01), Harris et al.
patent: 5856217 (1999-01-01), Nguyen et al.
patent: 5929467 (1999-07-01), Kawai et al.
Kruppa et al. “Low-frequency dispersion characteristics of GaN HFETs”Elect. Lett.(1995) 31(22):19511952.
Suzuki Akira
Teraguchi Nobuaki
Baumeister Bradley W.
Jackson, Jr. Jerome
Morrison & Foerster / LLP
Sharp Kabushiki Kaisha
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