InSb-based HEMT with over 300 GHz-fT using evaporated SiOx film

We fabricated nanoscale-gate Al
0.25
In
0.75
Sb/InSb high electron mobility transistors (HEMTs) grown on a (100) GaAs structure by molecular beam epitaxy (MBE) and measured their DC and RF performances at room temperature. The epitaxial structure had an electron mobility (μ) of 17,700 cm
²
/Vs with a sheet carrier concentration (N
s
) of 1.06×10
¹²
cm
⁻²
. We also introduced an evaporated SiO
x
passivation film instead of SiO
x
and SiN deposited by CVD method to prevent plasma damage in the passivation deposition process. As the result, we obtained a maximum transconductance (g
m_max
) of 0.88 S/mm and a cutoff frequency (f
T
) of 302 GHz for the 50-nm-gate HEMT when biased at a drain-source voltage (V
ds
) of 0.5 V, which was because the evaporated SiO
x
passivation film could prevent electrical degradation of the HEMT structure caused by not only plasma damage but also thermal damage in whole HEMT fabrication process.