Experimental Investigation of Drain Noise in High Electron Mobility Transistors: Thermal and Hot Electron Noise

TL;DR

This study characterizes microwave noise in high electron mobility transistors at different temperatures, revealing that hot electron effects significantly contribute to noise beyond thermal sources, and suggests potential noise reduction strategies.

Contribution

It provides a comprehensive on-wafer noise analysis of mHEMTs, identifying hot electron noise as a key factor and proposing methods to mitigate it for improved device performance.

Findings

Thermal noise explains only part of the measured output noise.

Hot electron noise likely contributes significantly to excess noise.

Potential noise temperature reduction of up to 50% at cryogenic temperatures.

Abstract

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.