In a high power IMPATT (Impact Avalanche Transit Time) diode for generating high frequency signals two electrodes, anode (2) and cathode (1), are arranged with a semiconductor layer therebetween. Said semiconductor layer comprises a drift layer (7) for transport of charge carriers between the electrodes. The semiconductor layer is made of crystalline SiC and it is provided with means (9) adapted to locally increase the electric field in the drift layer substantially with respect to the average electric field therein for generating an avalanche breakdown at a considerably lower voltage across the electrodes than would the electric field be substantially constant across the entire drift layer.
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