| Summary: | 博士 === 國立臺灣大學 === 電機工程學系研究所 === 86 === Abstract:
Two-dimensional simulation of GaAs MESFET''s was presented
in this thesis. GaAs
MESFET''s have the advantage of having higher speed than Si
devices have, so they have
been widely used in high-speed applications especially today in wireless
communications. Ion-implanted planar gate power MESFET (no recess etching) is
suitable for the power amplifier in cellular phones in dual
mode operation because
it has high efficiency and linearity in the digital mode and
good efficiency in the
analog mode. However, because the power MESFET is always biased
at near pinch-off
region for low power consumption, the behavior of the device
near pinch-off is very
critical for the performance of the amplifier. The most
significant phenomena of the
MESFET near pinch-off is the substrate leakage. One way to
eliminate the substrate
leakage is to implant p-type ion (Be) to form a p-type buffer
under the channel.
Too low Be dose is not sufficient to prevent the substrate
leakage, yet too high dose
will reduce the saturation current and the breakdown voltage. With the help of
two-dimensional simulation, the optimal design of the ion-
implanted power mesfet was
obtained.
Furthermore, V-groove gate MESFET''s were simulated and an
interesting mechanism
of short channel effect we named the Drain-Induced Carrier
Accumulation (DICA) effect
was first found. An analytical model for the V-groove gate
MESFET was proposed. The
model fitted the simulation results very well and it has
meaningful parameters. The
substrate effects for the V-groove MESFET were simulated also.
The devices with three
substrates, the undoped GaAs , the undoped AlGaAs and the p-
doped substrate, were
simulated. For the one with the undoped GaAs substrate,
substrate leakage was found;
the device with the undoped AlGaAs, DICA effect; and the device
with the p-doped
substrate, both the substrate leakage and the DICA effect occurred.
In addition, ultra-high frequency V-gate MESFET was first
proposed to have ft
up to 47 Ghz in the optimal condition by 2-D simulation. The
device has submicron
gate length without resorting to expensive E-beam lithography
and delicate multilayer
of photoresist. It may be very useful for microwave amplifier in the future.
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