PHOTOCURRENT SPECTROSCOPY MEASUREMENTS OF SI-GE ALLOYS AND SUPERLATTICES

We used photocurrent spectroscopy at 300 K, 77 K and 4.2 K to investig ate the optical absorption processes of (001) Si-Ge strained layer sup erlattices and alloys with an average composition of 50%Si-50%Ge. We o bserved an evolution toward higher energies of the threshold in the ph otocurrent spectra as the period of the superlattices decreases, with the spectrum of the shortest period superlattices (2:2) approaching th at of the alloy. The energy dependence of absorption in these Si-Gr he terostructures is quite distinct from that measured in elemental silic on.