Traveling-wave amplification by interaction with a current in a semiconductor

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Abstract
The electrons of a semiconductor may interact with a quasielectrostatic wave guided by an external structure and produce amplification if their velocity is large enough. The mechanism of interaction is described by a perturbation theory, the results of which are always valid near the threshold of amplification. The interaction occurs through the charges which are induced on the surface of the semiconductor by the electric field of the wave. The gain is proportional to an ’’effective resistance’’ of the semiconductor and to the excess of the drift velocity of surface electrons over a threshold velocity which is a characteristic of the line and is affected by space harmonics. Surface states may have a very important effect on the interaction. An experiment is presented, which is in agreement with the theory. Quasimagnetostatic surface waves may also be amplified. The interaction occurs through the current due to Lorentz’s force in the bulk of the semiconductor. The gain is proportional to the inverse of the effective resistance.