High−frequency limitation on silicon IMPATT diode: Velocity modulation

The effects of the energy relaxation time on the carrier velocity in silicon semiconductor materials is considered in the millimeter wave range. For this purpose an approximate formula relating the carrier velocity evolution in large−signal operation has been derived. Its influence on the rf output power and efficiency of the silicon IMPATT oscillator is discussed. Numerical results achieved reveal that the velocity modulation is one of the fundamental effects which limit the efficiency and power delivered at high frequencies; for example, at 100 GHz it causes an efficiency diminution which can exceed 30%.