Relaxation of the impurity photoconductivity in p-Ge/Ge_(1-x)Si_x quantum well heterostructures

摘要

In this paper we report a study on relaxation of the impurity photoresponse in strained p-Ge/GeSi heterostructures excited by pulsed THz radiation. The relaxation time is found to increase with the applied dc electric field, which is interpreted within the model of cascade carrier capture by the impurity centers. A second time scale of the impurity photoconductivity relaxation is observed near the impurity breakdown field, and in post-breakdown electric fields the relaxation time (decreasing with the field) is shown to be governed by the impact ionization rather than by the recombination.