Exciton condensation in the compressively strained SiGe layers of Si/SiGe/Si heterostructures

Abstract

The photoluminescence spectra of type-I alignment Si/Si 1 − x Ge x /Si heterostructures contained thin Si 1 − x Ge x layers ( d = 25–70 nm) are studied under various temperatures and excitation intensities. It was shown, excitation intensity increase at low temperatures leads to the exciton condensation resulting electron–hole liquid (EHL) formation in Si 1 − x Ge x layer. Electron–hole pair density n 0 and binding energy of the EHL relative to exciton gas φ decrease noticeably while х increases. The decrease in the binding energy and density of the electron–hole liquid is attributed to splitting of conduction and valance bands due to internal strains in the Si 1 − x Ge x layer. The Mott transition (from the exciton gas to electron–hole plasma) occurs above the critical temperatures for high excitation intensities.