Optimisation of abrupt emitter-base junction for heavily Be-doped InP/In/sub 0.53/Ga/sub 0.47/As heterojunction bipolar transistor

The optimisation of an abrupt emitter-base n-p junction for an InP/In/sub 0.53/Ga/sub 0.47/As heterojunction bipolar transistor has been carried out for heavily Be-doped In/sub 0.53/Ga/sub 0.47/As, with Be concentration ranging from 4.4 /spl times/ 10/sup 19/ cm/sup -3/ to 1.2 /spl times/ 10/sup 20/ cm/sup -3/. The electrical conductivity continuously increases even for the highest Be concentrations. Beryllium diffusion and segregation are strongly reduced by lowering the MBE growth temperature to 400/spl deg/C and less. Combined with precise adjustment of the thickness of an undoped spacer layer, it leads to high quality emitter-base junctions. Nearly ideal emitter-base I-V characteristics have been obtained for a doping level around 1 /spl times/ 10/sup 20/ cm/sup -3/, allowing ultra-high frequency HBTs with a base width as thin as 20 nm.