Gallium phosphide high-temperature bipolar junction transistor

Preliminary results are reported on the development of a high temperature (more than 350 C) gallium phosphide bipolar junction transistor (BJT) for geothermal and other energy applications. This four layer (p(+)n(-)pp(+) structure was formed by liquid phase epitaxy using a supercooling technique to insure uniform nucleation of the thin layers. Magnesium was used as the p-type dopant to avoid excessive out-diffusion into the lightly doped base. By appropriate choice of electrodes, the device may also be driven as an n-channel junction field-effect transistor. The gallium phosphide BJT is observed to have a common-emitter current gain peaking in the range of 6 to 10 (for temperature from 20 C to 400 C) and a room temperature, punchthrough-limited, collector-emitter breakdown voltage of approximately 6V. Other parameters of interest include an foub-t = 400 KHZ (at 20 C) and a collector base leakage current = 200 micro A (at 350 C).