QUANTUM WELLS IN OPTOELECTRONICS: Laser-induced transient photoconductivity in MQW systems

Abstract

In the interpretation of laser-induced transient photoconductivity a number of effects have to be taken into account. The most important of these are considered to be those associated with excitons, degeneracy, photon recycling, mobility variations and the nonuniformity of carrier injection. These effects are discussed and modifications are made, by including the boson character of the exciton and its four-fold spin degeneracy, to the theory of radiative recombination. A simple estimate of the effect of photon recycling in thin MQWs is given. The density dependence of mobility in an electron-hole plasma is argued to be small, except when higher subbands become populated or the quantum wells become full. In the latter case saturation of the photoconductivity, which can occur at low laser intensities with nonuniform injection, is expected. The importance of both the exponential decay in the degenerate regime and the observed intensity dependence of the initial amplitude is emphasised.