Phase transitions in a two-dimensional system of dipolar excitons in a double-well SiGe/Si heterostructure

Abstract

The transition from a dipolar electron–hole liquid (EHL) to a spatially direct one in two-dimensional layers of a type II (buffer Si_1–yGe_y)/tSi/sSi_1–xGe_x/tSi/(cap Si_1–yGe_y) heterostructure is studied via photoluminescence spectroscopy at helium temperatures and high excitation levels. This transition occurs when the sSi_1–xGe_x barrier layer for electrons (a quantum well (QW) for holes), that separates electron QWs (tSi layers) gets thinner. The basic parameters of both types of EHLs and the lifetime of dipolar excitons are determined.