Design and Investigation of a Metamorphic InAs Channel Inset InP HEMT for Cryogenic Low-Noise Amplifiers

This work proposes a 100 nm metamorphic InP HEMT with an InAs channel inset for cryogenic environment millimetre wave applications. The usage of an ultra-thin 2 nm barrier layer, unique composite channel topology and III-V material selection provides superior electron confinement in the channel, enhancing 2DEG concentration and mobility, thereby improving the speed of the proposed device. We achieve a unity current gain frequency (
$f_{\mathrm {T}}$
) of 248.9 GHz and a maximum oscillation frequency (
$f_{\mathrm {MAX}}$
) of 523.9 GHz with a current gain of 67.7 dB at 0.1 GHz, 298 K. A
$f_{\mathrm {T}}/f_{\mathrm {MAX}}$
of 5.02 GHz/10.01 GHz is achieved at 90 K. Off-state leakage current is in the nanoampere range with minimum noise figure (
$NF_{\mathrm {MIN}}$
) of only 0.09 dB at 10 GHz, 90 K. We compare the DC, RF, noise and parasitic characteristics of the proposed device with other composite channel InP HEMTs proposed in latest works and showcase performance improvements in all domains. The performance achieved by using an InAs insert specifically is also justified, with InGaAs-InAs-InGaAs channel HEMTs providing 1.4 times better
$f_{\mathrm {T}}$
and
$f_{\mathrm {MAX}}$
with only half the NFMIN of their InGaAs-InP-InGaAs channel counterparts. The proposed composite channel device showcases anomalous trends in electron scattering rate and electron mobility with impurity concentration and temperature variation. A novel frequency-and-temperature dependent small signal model has been put forth which accounts for these atypical cryogenic trends to accurately predict the behavior of the device under varying RF and temperature conditions.