Investigations of Novel $\Gamma$-Gate MOS-HEMTs by Ozone Water Oxidation and Shifted Exposure Techniques

A novel Γ-gate Al
_0.24
Ga
_0.76
As/In
_0.15
Ga
_0.85
As metal-oxide-semiconductor (MOS) high-electron-mobility transistor (MOS-HEMT) by using methods of ozone water oxidation and shifted exposure has been comprehensively investigated. Effective gate-length reduction, improved gate insulation, and formations of a field plate and a full surface passivation within the drain-source region are simultaneously achieved. The present Γ-gate MOS-HEMT has demonstrated superior device performances, including improvements of 523% (12.8%) in two-terminal gate-drain breakdown, 137% (36.1%) in on-state drain-source breakdown, 16.1% (11.8%) in maximum extrinsic transconductance (
gm
, max), 34.5% (9.7%) in intrinsic voltage gain (
AV
), 27.8% (16.2%) in power-added efficiency, 34.5% (19.8%) in minimum noise figure (
NF
_min
) , and 28%/39.3% (11.4%/21.6%) in unity-gain cutoff frequency/maximum oscillation frequency (
fT
/
f
_max
), as compared to a conventional Schottky-gate (MOS-gate) device fabricated upon the same epitaxial structure by using an identical optical mask set. Investigations of optimum extracted parasitics, small-signal device parameters, and high-temperature device characteristics at 300 K-450 K are also made in this work.