Measurement of the band gap of Ge<i>x</i>Si1−<i>x</i>/Si strained-layer heterostructures

Abstract

We have used photocurrent spectroscopy to measure the optical absorption spectra of coherently strained layers of GexSi1−x grown on 〈001〉 Si by molecular beam epitaxy. A dramatic lowering of the indirect band gap, relative to that of unstrained bulk Ge-Si alloys, is observed. Our results for 0≤x≤0.7 are in remarkably good agreement with recent calculations of the effects of misfit strain on the band edges of coherently strained Ge-Si heterostructures. At x=0.6, the gap is lower than that of pure Ge.