Power flow and carrier-wave interactions in semiconductors

Small-signal traveling-wave amplification and Gunn effect in semiconductors are discussed from the power flow point of view. Both phenomena give rise to instabilities that are of resistive character in the sense that they depend essentially on finite relaxation time. The known conditions for traveling-wave amplification--carrier drift velocity larger than the phase velocity--and for the Gunn effect --negative differential mobility--are verified when there is a negative loss in the semiconducting medium.