The transient response of quasi-two-dimensional semiconductors under hot electron conditions

Abstract

In calculating the transport properties of semiconductors in the presence of high electric fields, one must consider the effects of both the momentum, energy, and population-transfer relaxation times of the individual valleys, or quantum levels in a quasi-two-dimensional system. In recent calculations of hot electron microwave conductivities of quasi-two-dimensional silicon 〈100〉 samples it was found that the microwave conductivity at a fixed bias electric field showed non-monotonic behavior when plotted as a function of frequency, and has a conductivity peak in the high frequency region. To further clarify this conductivity peak and its implications for velocity overshoot, we have carried out transient response solutions to the electron transport for both large-signal and small-signal conditions. In this paper, the results of these calculations for electrons in a 〈100〉 inversion layer are reported. The response of the electron gas to a large dc field step and to a small step applied upon a large dc bias field are calculated. Much of the velocity overshoot and ac conductivity peaking are related to the differential repopulation among the inequivalent valley sub-bands.