Silicon-on-sapphire bipolar transistors

All-epitaxial bipolar transistors have been fabricated in silicon-on-sapphire films which exhibit a common-emitter low frequency current gain hfeof 10 at room temperature. The value of hfeincreases approximately as the square of the absolute temperature, which suggests recombination by charged coulomb centers in the base region. Monotonic increase in hfewith collector current up to 100 mA (emitter area is 0.8 × 1.2 sq. mils) is probably due to trap-filling in the base region. No conductivity modulation, which would result in beta fall-off, is seen up to 500 mA of collector current. This is a narrow ( M), heavily doped ( cm^-3) base region.