Low noise GaAs varactor and mixer diodes prepared by molecular beam epitaxy

Schottky-barrier varactor and mixer diodes have been made from Ge-doped GaAs layers grown by molecular beam epitaxy. A microstrip parametric amplifier circuit incorporating a hyperabrupt varactor diode has given a noise temperature of 120 K and bandwidth of 180 MHz at 15 dB gain when pumped at 34 GHz, and a mixer diode mounted in a cryogenic receiver circuit had an s.s.b. noise temperature of 180 K at 90 GHz.