Temperature dependence of DC characteristics of Si/SiGe heterojunction bipolar transistors

Silicon/silicon-germanium heterojunction bipolar transistors incorporating a strained layer of silicon - germanium alloy have been fabricated and their DC characteristics investigated over a wide range of temperatures (80 to 400K). The collector currents were typically found to be ideal over six orders of magnitude at room temperature. Nonideal behaviour observed below 180K is ascribed to surface recombination effects. The mechanisms associated with the nonideal behaviour of the base currents are discussed and the enhanced ideality seen towards 400K assigned to a reduced dominance of recombination mechanisms.