Interband absorption in alpha-Sn/Ge short-period superlattices

Band-to-band infrared absorption has been studied in a series of Sn1Gem (m=11, 15, and 21) strained layer superlattices for the first time. The absorption coefficient shows a quadratic increase with two onsets, characteristic for indirect transitions. From a numerical fit to the absorption spectra, band gap energies are determined in the energy range between 0.55 and 0.75 eV, in accordance with theoretical calculations. The temperature dependence of the band gaps show the usual behavior, at low temperatures quadratic and at higher temperatures linear decrease with increasing temperature. Applied Physics Letters is copyrighted by The American Institute of Physics