Optimized Buffer Stack with Carbon-Doping for Performance Improvement of GaN HEMTs

This paper focuses on determining an optimized value of carbon-doping level in the buffer and corresponding channel thickness to improve the performance of GaN HEMTs in terms of subthreshold slope
$(SS)$
, breakdown voltage
$(V_{BD})$
and transit frequency
$(f_{t})$
. With the increase in carbon-doping, we observe improvements in
$SS$
and
$V_{BD}$
while the
$f_{t}$
is reduced. However, as the channel thickness increases above a certain thickness, no significant impact of carbon-doping is observed on the characteristics. TCAD simulation is calibrated using experimental data for a device with carbon-doping level of
$3\times 10^{18}cm^{-3}$
in the buffer with channel thickness of 500 nm. Using the calibrated device in TCAD, the carbon-doping level and channel thickness are varied to see the effects on different parameters. We observed that an optimized channel thickness of 200 nm with carbon-doping level of
$1\times 10^{19}cm^{-3}$
in the buffer yields the best results in terms of
$V_{BD}$
and
$f_{t}$
.