Investigation of drain noise in InP pHEMTs using cryogenic on-wafer characterization

We present on-wafer measurements of microwave noise temperature and S-parameters of InP pseudomorphic high electron mobility transistors (pHEMTs) over various drain-source voltages (V
DS
) and physical temperatures (T
ph
). From these data, we extract the small signal model (SSM) and drain noise temperature T
d
at each V
DS
and T
ph
. We find that T
d
follows a non-linear trend with both V
DS
and T
ph
. The observed trends are consistent with a recent drain noise model [1], [2], where T
d
originates from the sum of a thermal noise, attributed to physical temperature of electrons (T
el
) in the channel; and real-space transfer (RST) noise, attributed to thermionic emission of electrons from the channel to the barrier. Using this model, we find that at the bias that minimizes the noise temperature, RST accounts for ∼ 50% of T
d
at 300 K and ∼ 30 % at 40 K. Possible improvements in noise performance in pHEMTs if RST were suppressed are discussed.