BAND-EDGE EMISSION FROM STRAINED SIGE ALLOY LAYERS ON GE(100) SUBSTRATES

We have fabricated strained SixGe1-x/SiyGe1-y multiple quantum wells o n Ge(100) substrates an measured the photoluminescence (PL) spectra, o bserving band-edge emission from the SiGe alloy layers. The emission i s due to the recombination of both bound excitons and free excitons in the quantum wells. From the positions of the observed PL lines, we ha ve evaluated the band-gap energies of the strained SiGe alloy layers, and found them to be smaller than those of bulk SiGe alloys. The band- gap energy increases with the Si content of the alloy, reaching a maxi mum at about 15% Si, and subsequently decreases. These results agree w ell with the theoretical calculations for strained layers, and suggest a type II band alignment in some cases for SixGe1-x/SiyGe1-y heterost ructures on Ge(100).