GaInP epitaxial stacking structure and fabrication method...

Details GaInP epitaxial stacking structure and fabrication method... GaInP epitaxial stacking structure and fabrication method...

2000-09-15

2002-10-08

Prenty, Mark V. (Department: 2822)

Active solid-state devices (e.g., transistors, solid-state diode

Heterojunction device

Field effect transistor

C257S015000

Reexamination Certificate

active

06462361

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a GaInP epitaxial stacking structure, and more specifically to a GaInP epitaxial stacking structure for FETs and a fabrication method thereof, which has electron-supply layers and spacer layers which give high-mobility characteristics, and a high-mobility field effect transistor using this structure.
2. Description of the Prior Art:
Schottky junction-type field effect transistors (known as MESFETs) which operate in the microwave region or millimeter wave region include GaInP high electron mobility transistors (known as TEGFETs, MODFETs and the like) which utilize mixed crystals of gallium-indium phosphide (Ga
A
In
1−A
P: 0≦A≦1) (see
IEEE Trans. Electron Devices
, Vol. 37, No. 10 (1990), pp. 2141-2147). GaInP MODFETs can be used as low-noise MESFETs for signal amplification in the microwave region (see
IEEE Trans. Electron Devices
, Vol. 46, No. 1 (1999), pp. 48-54) and as power MESFETs for transmission applications (see
IEEE Trans. Electron Devices
, Vol. 44, No. 9 (1997), pp. 1341-1348).
FIG. 1
is a schematic diagram of the cross-sectional structure of a conventional GaInP TEGFET. The substrate
10
used is made of semi-insulating gallium arsenide (chemical formula: GaAs) with a {001} crystal plane as its primary plane. Upon the substrate
10
is deposited a buffer layer
11
consisting of a high-resistance Group III-V compound semiconductor layer. Upon the buffer layer
11
is deposited an electron transporting layer (channel layer)
12
consisting of n-type mixed crystals of gallium-indium arsenide (Ga
Z
In
1−Z
As: 0<Z≦1). A spacer layer may be deposited upon the channel layer
12
, but particularly in power TEGFETs for transmission applications, an electron-supply layer
13
consisting of mixed crystals of gallium-indium phosphide (Ga
Y
In
1−Y
P: 0<Y≦1) is deposited without an interposed spacer layer. The carrier (electron) density of the electron-supply layer
13
is adjusted by the intentional addition (doping) of silicon (Si) or other n-type impurities which are not readily diffused. Upon the electron-supply layer
13
, a contact layer
14
consisting of n-type GaAs or the like is typically provided in order to form the low-contact resistance source electrode
15
and drain electrode
16
. In addition, between the source and drain electrodes
15
,
16
, the contact layer
14
is partially removed to expose a recess structure, and a Schottky junction-type gate electrode
17
is provided, thereby constituting a TEGFET.
The various constituent layers
11
-
14
which constitute the GaInP epitaxial stacking structure
1
A for MODFET application illustrated in
FIG. 1
, because of their ease of film formation, are conventionally formed by the metal-organic chemical vapor deposition (MOCVD) method (see ibid
IEEE Trans. Electron Devices
, Vol. 44 (1997)). Among these constituent layers, the electron-supply layer
13
is a functional layer for supplying electrons formed to accumulate as a two-dimensional electron gas (TEG) in the vicinity of the junction interface
12
a
of the channel layer
12
. The electron-supply layer
13
is conventionally formed of gallium-indium phosphide (Ga
Y
In
1−Y
P: 0<Y≦1) doped with silicon (the symbol of element: Si) or other n-type impurities which are not readily diffused (see ibid
IEEE Trans. Electron Devices
, Vol. 44 (1997)). The carrier density (units: cm
−3
) of the electron-supply layer
13
is commonly made 1-3×10
18
cm
−3
or 2×10
18
cm
−3
in particular. The thickness of the layer is typically set within the range 10 nm to 40 nm. In addition, in a GaInP TEGFET, the n-type electron-supply layer is normally constituted from Ga
Y
In
1−Y
P (0<Y≦1) layers wherein the gallium composition ratio (=Y) is fixed in the layer thickness direction.
In addition, in the structure wherein a spacer layer is deposited upon the channel layer
12
, in order to prevent the two-dimensional electron gas from being disturbed due to ionization scattering from the channel layer
12
, the spacer layer is a functional layer provided for the spatial isolation of the channel layer
12
and electron-supply layer
13
(see “Physics and Applications of Semiconductor Superlattices,” Physical Society of Japan, ed. (published by Baifukan, Sep. 30, 1986, first edition, fourth printing), pp. 236-240). In a GaInP TEGFET, the spacer layer is typically constituted from undoped Ga
X
In
1−X
P (0<X≦1) (see ibid
IEEE Trans. Electron Devices
, Vol. 44 (1997)). Regardless of the case of GaInP TEGFET, spacer layers are constituted from high-purity undoped layers with a low total amount of impurities, and their layer thickness is typically in the range from 2 nanometers (nm) to 10 nm (see ibid “Physics and Applications of Semiconductor Superlattices,” pp. 18-20).
For example, in a low-noise GaInP TEGFET, the noise-figure (NF) and other major properties vary depending on the electron mobility, so the higher the electron mobility, the lower the NF conveniently becomes. For this reason, in order to cause the electrons supplied from the n-type electron-supply layer
13
to accumulate as a two-dimensional electron gas in the interior regions of the Ga
Z
In
1−Z
As (0<Z≦1) in the vicinity of the junction interface with the spacer layer consisting of undoped Ga
X
In
1−X
P (0<X≦1), the composition at the junction interface between the channel layer
12
and the spacer layer must change abruptly and exhibit high electron mobility.
In addition, the formation of a buffer layer is typically performed by vapor deposition without varying the starting material species of gallium (element symbol: Ga). Since the admixture of carbon (element symbol: C) acceptors that electrically compensate residual donor components represented by silicon occurs readily, and a high-resistance GaAs layer or Al
L
Ga
1−L
AS layer is easily obtained in the undoped state (see
J. Crystal Growth
, 55 (1981), pp. 255-262), trimethyl gallium (chemical formula: (CH
3
)
3
Ga) is used as the gallium (Ga) source (see
J. Crystal Growth
, 55 (1981), pp. 246-254, ibd, pp. 255-262, and PCT application publication No. 10-504685).
In a GaInP TEGFET for low-noise amplification, the noise-figure (NF) and other major properties vary depending on the two-dimensional electron mobility (units: cm
2
/N·s), so the higher the electron mobility (cm
2
/N·s), the lower the NF becomes. For this reason, in a low-noise TEOFET, the electron-supply layer which takes the role of supplying electrons must be constituted from Ga
Y
In
1−Y
P (0<Y≦1) which can exhibit a high electron mobility. On the other hand, in a power TEGFET, from the standpoint of causing it to operate with a relatively large source-drain current flowing, a large sheet carrier density (units: cm
−2
) is required together with the electron mobility. Therefore, electron-supply layer for power TEGFET applications must be constituted from a Ga
Y
In
1−Y
P (0<Y≦1) layer that exhibits a high sheet carrier density.
However, in the conventional electron-supply layer consisting of Ga
Y
In
1−Y
P wherein the gallium composition ratio (=Y) or indium composition ratio (=1−Y) is roughly constant, at a relatively high sheet carrier density, there is a disadvantage in that a high electron mobility cannot be manifested stably. For this reason, in low-noise GaInP TEGFETs for example, a large transconductance (g
m
) is not obtained, thus obstructing the stable supply of low-noise GaInP TBGFBTs with a superior low noise-figure (NF).
A first object of the present invention is to provide a GaInP epitaxial stacking structure containing a Ga
Y
In
1−Y
P (0<Y≦1) electron-supply layer and fabrication method thereof for stably manifesting a high electron mobility in excess of 5000 cm
2
/V·s at room temperature and at a relatively high sheet carrier density of 1.5×10
12
cm
2
or greater and 2.0×10
12
cm

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