Fundamental high-frequency performance limit for impatt mode operation

It is well known that the phase delay associated with carrier energy relaxation in impatt diodes tends to improve their performance. The purpose of the letter is to point out that there is also an amplitude degradation effect which tends to impair impatt performance. At high enough frequencies the amplitude degradation effect dominates, leading to a high-frequency performance roll-off. The net effect of energy relaxation is believed to be deleterious for frequencies above about 500 GHz for Si devices, and at lower frequencies for GaAs devices.