First-principles optical properties of Si/CaF2 multiple quantum wells

The optical properties of Si/CaF2 multiple quantum wells are studied ab initio by means of the linear-muffin-tin-orbital method. In particular, we investigate the dependence of the optoelectronic properties on the thickness of the Si wells. We find that below a well width of similar to 20 Angstrom, new transitions appear in the optical region with an evident polarization dependence. The oscillator strength of these transitions shows a dramatic increase as the width of the Si well decreases. A comparison is made with recent experimental work on similar systems. Our results show that quantum confinement and passivation are necessary in order to have photoluminescence in confined silicon-based materials.