Type-II band alignment in Si/${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$ quantum wells from photoluminescence line shifts due to optically induced band-bending effects: Experiment and theory

We compare measured energy shifts of photoluminescence lines in Si/${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Ge}}_{\mathit{x}}$ quantum wells as a function of excitation power with theoretical calculations to conclude that the band alignment of the heterointerface is type II. Experimentally, we study molecular-beam epitaxy-grown fully strained Si/${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Ge}}_{\mathit{x}}$ single quantum wells with Ge fractions from 10% to 36%. These show significant blueshifts of the luminescence at increasing excitation density. Theoretically, we calculate self-consistently transition energy changes taking into account band bending due to the photoinduced charge carriers. Only for type-II band alignment are the experimental and theoretical results compatible.