Hot electron injection in millimetre wave Gunn diodes

Abstract The use of graded aluminium composition layers of AlGaAs alloys, together with a modified doping profile at the beginning of the drift region, has resulted in 94 GHz GaAs-based heterojunction Gunn diodes with room temperature power exceeding 70 mW, and a performance whose frequency stability between −40C and +80C is much better than achievable in homojunction GaAs Gunn diodes over the same temperature range. The output power versus applied bias is high and relatively constant over a much wider range of bias when heterojunction designs are used, which greatly assists circuit designers. Exceptionally low noise levels have also been achieved. The relevant physics of hot electron injection into the drift region of a Gunn diode is described, and we explain how this injection results in improved device performance. Extensive simulation studies complement the practical device design, and interpretation of device results.