InAs bipolar transistors: a path to high-performance cryogenic electronics

The authors present the first demonstration of npn InAs bipolar transistors operating under room temperature and cryogenic conditions. The development of InAs HBTs (heterojunction bipolar transistors) has been hindered by the lack of a suitable wide bandgap emitter. This problem is circumvented by using the pseudo-HBT concept, which relies on the Burnstein shift to effectively widen the bandgap in the n-emitter and bandgap narrowing in the heavily doped p-type base to effectively shrink the base bandgap. For low temperature operation, the resulting bandgap difference should be more than sufficient for a wide-gap emitter as demonstrated by the current gains of more than 100 observed in GaAs pseudo-HBTs operating at 35 K.