Current gain enhancement for silicon-on-insulator lateral bipolar junction transistors operating at liquid-helium temperature

Conventional homojunction bipolar junction transistors (BJTs) are not suitable for cryogenic operation due to heavy doping-induced emitter band-gap narrowing and strong degradation in current gain ( $\beta $ ) at low temperature. In this letter, we show that, on lateral version of the BJTs (LBJTs) fabricated on silicon-on-insulator (SOI) substrate, such $\beta $ degradation can be mitigated by applying a substrate bias ( ${V}_{sub}$ ), and a $\beta $ over unity is achieved in a base current ( ${I}_{B}$ ) range over 5 orders of magnitudes at 4.2 K, with a peak $\beta \sim 100$ demonstrated. The $\beta $ improvement is explained by the enhanced electron tunneling through base region as a result of base barrier lowering and thinning by a positive ${V}_{sub}$ , which leads to dramatic increase of collector current ( ${I}_{C}$ ) while ${I}_{B}$ is negligibly affected.