OPTICAL-ABSORPTION SPECTROSCOPY OF SI-GE ALLOYS AND SUPERLATTICES

We report calculations and measurements of the optical absorption coef ficient of SinGem superlattices and alloys where n approximate to m. O ur results can be used to determine the fundamental band gap, the depe ndence of the band gap on superlattice period, and the absorption coef ficient near the band-gap energy. Both theory and experiment show that all short-period (n+m<20) superlattices display a similar linear depe ndence of absorption coefficient on photon energy. This behavior is di fferent from alloys of the same average composition where we measure t hat the absorption coefficient increases with the 3/2 power of photon energy.