Collector current transport mechanisms in SiGE HBTs operating at cryogenic temperatures
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Silicon germanium heterojunction bipolar transistors (SiGe HBTs) have recently gained attention due to their potential for use in quantum computing readout circuits. To serve such applications, which requires low noise, low to medium speed, and low power, it is crucial to understand the transport physics of SiGe HBTs at cryogenic temperatures. This thesis aims to extend the existing transport theories for collector current through theoretical analysis, experimental data, and TCAD simulation. A novel transport mechanism, namely the direct tunneling mechanism, is found to account for a portion of collector current at cryogenic temperatures. A method is proposed to differentiate between direct tunneling and quasi-ballistic transport. With the understanding of collector current and its physics, the impact of technology scaling on future SiGe HBTs are evaluated.