Operation of SiGe heterojunction bipolar transistors in the liquid-helium temperature regime
- 1 June 1995
- journal article
- Published by Institute of Electrical and Electronics Engineers (IEEE) in IEEE Electron Device Letters
- Vol. 16 (6) , 268-270
- https://doi.org/10.1109/55.790731
Abstract
We present the first dc measurements of silicon-germanium (SiGe) heterojunction bipolar transistors (HBTs) operating in the liquid-helium temperature (LHeT=4.2 K) regime. The current gain of the self-aligned, UHV/CVD-grown SiGe HBT increases monotonically from 110 at 300 K to 1045 at 5.84 K, although parasitic base current leakage limits the useful operating current to above about 1.0 /spl mu/A at 5.84 K. An aggressively designed base profile (peak N/sub AB//spl ap/8/spl times/10/sup 18/ cm/sup -3/) is used to suppress base freeze-out at LHeT (R/sub bi/=18.3 k/spl Omega///spl square/ at 4.48 K). We have also identified a non-ideal minority carrier transport mechanism in the collector current at temperatures below 77 K (I/sub C/ is not proportional to exp(qV/sub BE//kT)) which is unaccounted for in conventional device theory. Preliminary calculations suggest that this phenomenon is due to trap-assisted carrier tunneling from the emitter to the collector through the base potential barrier.Keywords
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