Theory of Electron-Phonon Interaction Responsible for Current Saturation Phenomena in Semiconductors

Abstract

A theory applicable over the whole range of ql is presented for electron-phonon interaction responsible for the current saturation phenomena in semiconductors. Transport equations are set up by the nonequilibrium Green's function technique. The equations show clearly that phonons play two different physical roles in the description of transport phenomena; one is to act on electrons as waves and the other is to interact with them as quasiparticles. As for amplification of phonons as quasiparticles, calculation shows that the radical reduction of amplification factor is not expected even when ql ≪ 1. In the case of high-mobility semiconductors, the quasiparticle aspect is applicalbe in the initial stage of amplification, but the wave aspect is expected to appear in the final stage. The amplification of waves is discussed in the nonlinear regime. To the second order approximation, it is shown that the amplification factor is decreased with increase of the wave amplitude. The domain problem is studied by using an electronic computer. It is certain that the domain formation is irrelevant to the Ridley mechanism.