Photoluminescence from pseudomorphic Si1−xGex quantum wells grown by molecular beam epitaxy: Variation of the band gap with high pressure

Abstract

We report the first observation of truly near-edge photoluminescence (PL) from molecular beam epitaxy (MBE) prepared, narrow, strained-epitaxial Si/Si1−xGex quantum wells. Indeed, PL intensity from just two 25-Å wells is comparable to that from the free exciton in high-quality Si−thus reflecting the achievement of excellent MBE-epilayer quality. As importantly, we also report the first measurement of the variation of quantum-well emissions with applied hydrostatic pressure. A clear no-phonon emission line is found in the low-temperature (6 K) PL which displays, versus pressure, a strictly linear dependence in emission energy, with a slope virtually identical to that of the Si free exciton. This result is strong evidence that this quantum-well emission process is indeed ‘‘shallow’’ in origin, and is associated with the lowest, indirect X1-gap transition in these strained (unrelaxed) structures. Furthermore, these results provide circumstantial evidence that the band alignment in this system is effectively type I.