Impact of the channel thickness fluctuation on the subthreshold swing of InGaAs HEMTs at cryogenic temperature down to4K for ultra-low power LNAs

III-V-based device, especially InGaAs HEMT, is one of the most promising technologies in cryogenic low-noise amplifiers (LNAs) and switching circuits in the GHz range for quantum computing (QC) applications. For large-scale QC systems such as thousands to millions of qubits, LNA with desirable noise characteristics operating at a power level of at least a few hundred microwatts is needed. Consequently, achieving a high g
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ratio at a low current level becomes paramount, making the subthreshold swing (SS) value a crucial factor. Despite this, InGaAs HEMTs exhibit SS saturation at cryogenic temperatures, a phenomenon that remains largely unexplored and misunderstood. In this work, for the first time, we present and analyze the saturation mechanism in cryogenic InGaAs HEMTs. A novel interpretation of the phenomenon is proposed, predicated on the disorder resulting from potential fluctuations in the channel, attributable to the variability in channel thickness. We have discovered that the extent of potential fluctuation, induced by the fluctuation in channel thickness, differs according to the channel structure, which subsequently influences the degree of disorder. This research underscores the importance of an in-depth understanding of the fundamental phenomena of SS saturation level governing the performance of InGaAs HEMTs in ultra-low power regions and paves the way for the refinement of device design and operation in the field of LNA for quantum computing.