Investigation of Condensation of Excitons in Germanium by Light-Scattering Method

Abstract

L. V. Keldysh [1] suggested in 1968 that a system of Wannier—Mott excitons in a semiconductor may undergo a phase transition similar to the first-order phase transition in a gas—liquid system. When the exciton density in the semiconductor exceeds a certain threshold value corresponding to the given temperature (for temperatures below the critical temperature), the excitons condense into “liquid” droplets, the electrons and holes in which are collectivized and bound by the forces of internal interaction.

The basic properties of the condensed phase of excitons are studied and the possibilities of the light-scattering method of investigating the phase transition in which an exciton gas condenses into electron-hole drops are assessed. A very sensitive setup developed especially to study light scattering electron-hole drops is described. The kinetics of exciton condensation is studied via the measured dependence of the dimensions and concentration of the electron-hole drops on temperature, intensity, and method of excitation. The density and surface tension of the electron-hole liquid are measured. A model of exciton condensation is considered in which liquid-phase nucleations are formed as a result of fluctuations of the exciton density and in which the nucleations grow due to the diffusion of excitons toward their surface.