Kavli Affiliate: Austin J. Minnich
| First 5 Authors: Bekari Gabritchidze, Kieran A. Cleary, Anthony C. Readhead, Austin J. Minnich,
| Summary:
We report the on-wafer characterization of $S$-parameters and microwave noise
temperature ($T_{50}$) of discrete metamorphic InGaAs high electron mobility
transistors (mHEMTs) at 40 K and 300 K and over a range of drain-source
voltages ($V_{DS}$). From these data, we extract a small-signal model and the
drain (output) noise current power spectral density ($S_{id}$) at each bias and
temperature. This procedure enables $S_{id}$ to be obtained while accounting
for the variation of small-signal model, noise impedance match, and other
parameters under the various conditions. We find that the thermal noise
associated with the channel conductance can only account for a portion of the
measured output noise. Considering the variation of output noise with physical
temperature and bias and prior studies of microwave noise in quantum wells, we
hypothesize that a hot electron noise source based on real-space transfer of
electrons from the channel to the barrier could account for the remaining
portion of $S_{id}$. We suggest further studies to gain insights into the
physical mechanisms. Finally, we calculate that the minimum HEMT noise
temperature could be reduced by up to $sim 50$% and $sim 30$% at cryogenic
temperature and room temperature, respectively, if the hot electron noise could
be suppressed.
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