Indium phosphide (InP) high electron‐mobility transistors (HEMTs) are widely used in many fields such as quantum computing because of their unparalleled microwave noise performance. Achieving improved noise performance requires a physical understanding of the noise mechanisms. Here, we experimentally test a theoretical proposal for drain (output) noise as originating in part from real‐space transfer (RST) by characterizing the microwave noise temperature of transfer‐length method structures with the same channel composition but two different barrier compositions. This choice was made to alter the confining potential of electrons in the channel, thereby affecting the RST mechanism, while avoiding changes to the channel transport properties. We observe trends of noise temperature with physical temperature and source‐drain voltage which are compatible with the predictions of RST noise theory. This finding supports the hypothesis that RST generates microwave noise in InGaAs/InAlAs quantum wells used in modern InP HEMTs and therefore could contribute to drain noise. Additional study in full HEMT devices is needed to quantify its contribution relative to other effects such as impact ionization.
Zhang et al. (Tue,) studied this question.