NONIDEAL CURRENT-VOLTAGE CHARACTERISTICS IN MBE-GROWN SI1-XGEX SI HETEROJUNCTION BIPOLAR-TRANSISTORS/

The current-voltage characteristics of Si/Si1-xGex/Si heterojunction b ipolar transistors and Si homojunction bipolar transistors grown by MB E have been measured with the aim of elucidating the causes of degrade d common-emitter gain and low BVCEO. It is shown that high reverse dio de leakage currents arising from Zener tunnelling contribute to low BV CEO in all structures considered. In forward bias, recombination curre nts in the space charge layers are the dominant cause of excess base c urrent at temperatures above similar to 200 K. Below this temperature a defect-assisted tunnelling mechanism gives rise to diode non-idealit y.