BAND-GAP OF STRAIN-SYMMETRIZED, SHORT-PERIOD SI/GE SUPERLATTICES

We report an identification and determination of the band-gap energies in a series of strain-symmetrized Si(n)/Ge(n) superlattices. Absorption onsets are observed that shift toward higher energies with decreasing period length in superlattices with identical Si/Ge ratio. Band-gap energies of 0.67, 0.76, and 0.88 eV for Si6/Ge6, Si5/Ge5, and Si4/Ge4 superlattices, respectively, are determined by a fitting procedure. Strong photoluminescence and electroluminescence are observed for the Si5/Ge5 superlattices. The energetic position indicates that the luminescence is related to interband transitions.