SUPPRESSION OF GA-ATOM DIFFUSION AT GE/GAAS HETEROJUNCTION AND ITS APPLICATION TO HIGH-GAIN COLLECTOR-UP GE/GAAS HBTS

Ga-atom diffusion into Ge at Ge/GaAs heterointerfaces has been suppressed by using the two-step MBE growth of Ge, where a thin Ge film is grown on GaAs at low temperatures prior to Ge grow that 500-degrees-C. This technology is applied to base-layer formation in Ge/GaAs HBTs. The current gain of 430, the largest gain among the reported bipolar transistors with collector-top structure, has been achieved by an HBT with an undoped 150 angstrom-thick Ge film grown at 150-degrees-C. The suppression of Ga-atom diffusion gives rise to the reduction of base width and Auger recombination rate, resulting in the increase of the gain,