bration technique, IEEE Trans Microwave Theory Tech MTT-38
(1990), 8 –13.
6. J.A.R. Ball and B. Horsfield, Resolving ambiguity in broadband
waveguide permittivity measurements on moist materials, IEEE Trans
Instrum Meas 47 (1998).
7. Compilation of the dielectric properties of body tissues at RF and
microwave frequencies, see http://www.brooks.af.mil/AFRL/HED/
hedr/reports/dielectric/home.html.
8. C. Gabriel, S. Gabriel, and E. Corthout, The dielectric properties of
biological tissues. Part 1: Literature survey, Phys Med Biol 41 (1996),
2231–2249.
9. S.S. Stuchly, C.L. Sibbald, and J.M. Anderson, A new aperature ad-
mittance model for open-ended waveguides, IEEE Trans Microwave
Theory Tech MTT-42 (1994), 192–198.
© 2003 Wiley Periodicals, Inc.
Ga
0.51
In
0.49
P/In
x
Ga
1x
As/GaAs DOPED-
CHANNEL FETs (DCFETs) AND THEIR
APPLICATIONS ON MONOLITHIC
MICROWAVE INTEGRATED CIRCUITS
(MMICs)
Yo-Sheng Lin,
1
Chih-Chen Chen,
1
and Shey-Shi Lu
2
1
Department of Electrical Engineering
National Chi-Nan University
Puli, Taiwan, R.O.C.
2
Department of Electrical Engineering
National Taiwan University
Taipei, Taiwan, R.O.C.
Received 5 March 2003
ABSTRACT: In this paper, lattice-matched Ga
0.51
In
0.49
P/GaAs and
strained Ga
0.51
In
0.49
P/In
0.2
Ga
0.8
As doped-channel FETs (DCFETs) were
investigated in terms of DC and microwave performances, including
frequency response, noise figure, power-added efficiency (PAE), and
output power. In addition, small-signal and large-signal models were
created for designing monolithic microwave integrated circuits
(MMICs). The heterostructures were both grown by gas-source molecu-
lar beam epitaxy (GSMBE) on semi-insulating (100) GaAs substrates. In
situ reflection high-energy electron diffraction (RHEED) was used to
calibrate the growth rate of InP and GaP. Because of the high etching
selectivity between Ga
0.51
In
0.49
P and In
0.2
Ga
0.8
As/GaAs, the uniformity
of the measured electrical properties of our fabricated devices is quite
satisfying, which indicates that these Ga
0.51
In
0.49
P/In
x
Ga
1-x
As struc-
tures are very suitable for mass production. © 2003 Wiley Periodicals,
Inc. Microwave Opt Technol Lett 39: 56 – 62, 2003; Published online in
Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.
11126
Key words: strained; Ga
0.51
In
0.49
P; In
0.2
Ga
0.8
As; doped-channel FETs;
MMIC
1. INTRODUCTION
Heterostructure FETs (HFETs), based on an InGaAs pseudomor-
phic channel, have shown state-of-the-art performance at millime-
ter-wave frequencies as a result of good electron confinement by
their potential well, high-current drivability and high transconduc-
tance [1]. Therefore, device performance is enhanced substantially
by increasing the In content in the InGaAs channel. However,
these devices, including strained layers, are always restricted by
the so-called critical thickness [2]. It has been demonstrated that
there exist some difficulties in achieving high-quality 150-Å-thick
InGaAs films with an In content greater than about 0.15– 0.20 [3]
due to the increase of mismatched stress between AlGaAs and
InGaAs materials.
Because the gate is sitting directly on the undoped high-
bandgap layer, the pseudomorphic doped-channel FETs (DCFETs)
can achieve higher breakdown voltages compared with traditional
HEMTs or pHEMTs. It has been demonstrated that the current-
drivability and transconductance (g
m
) of metal/i-AlGaAs/n-In-
GaAs/i-GaAs quantum-well MISFETs with doped InGaAs chan-
nel were higher than those of metal/i-AlGaAs/i-InGaAs/n-GaAs
quantum-well MISFETs with undoped InGaAs channel [4]. In
addition, there are several advantages gained by using the
Ga
0.51
In
0.49
P/InGaAs material system compared with the AlGaAs/
InGaAs system [5]. Therefore, in this paper, we study the perfor-
mances of the metal/i-GaInP/n-GaAs/i-GaAs lattice-matched and
metal/i-GaInP/n-In
0.2
Ga
0.8
As/i-GaAs strained doped-channel FETs
(DCFETs).
2. CRYSTAL GROWTH AND DEVICE TECHNOLOGY
2.1. Calibration of Growth Conditions
The heterostructures used in this paper were grown by gas-source
molecular beam epitaxy (GSMBE) on semi-insulating (100) GaAs
substrates. First, in situ reflection high-energy electron diffraction
(RHEED) was used to calibrate the growth rate of InP and GaP, as
shown in Table 1. The calibration steps are as follows:
1. The growth rate of GaP was calibrated by growing GaAs on
a GaAs substrate, assuming the rate for growing GaAs for a
given Ga flux is the same as that for GaP.
2. The growth rate of InP was calibrated by growing InP on an
InP substrate. Since the lattice constant of InP is different
from that of GaAs, corrections were made to calibrate the
growth rate of InP on GaAs. The correction factor is (a_InP/
a_GaAs)
3
= 1.11877372.
3. To grow lattice-matched GaInP on a GaAs substrate, the
growth rate ratio (GaP on GaAs): (InP on GaAs) must be
0.51:0.49. However, the growth rate ratio of (GaAs on
GaAs):(InP on InP) must be 0.52:0.53, considering the
correction factor in step 2. As shown in Figure 1, the cell
temperature of Ga and In are 871°C and 876°C for growth
rate 0.52 m/hr (GaAs on GaAs) and 0.53 m/hr (InP on
InP), respectively.
4. The GaInP was then grown on GaAs according to the above
RHEED rate calibrations. X-ray diffraction of the sample
was used to determine the mismatch. With this mismatch
TABLE 1 RHEED Calibration of InP Grown on InP
and GaAs Grown on GaAs
Lattice constant of GaAs 5.65325 Å
Lattice constant of InP 5.86875 Å
Temp.
(Ga) Sec/Monolayer
1/Temp.
(1/K)
Rate
(m/hr.) log (Rate)
908 1.022 0.00084674 0.995680039 -0.00188
870 1.975 0.000874891 0.515232911 -0.28780
838 3.86 0.00090009 0.263623057 -0.57902
Temp.
(In) Sec/Monolayer
1/Temp.
(1/K)
Rate
(m/hr.) log (Rate)
900 1.134 0.000852515 0.89734127 -0.04704
880 1.763 0.000867303 0.57718945 -0.23868
860 2.662 0.000882613 0.382263336 -0.41764
840 4.103 0.000898473 0.248009993 -0.60553
56 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 39, No. 1, October 5 2003