Temperature dependence of energy gap of Ge1−x Sn x alloys with x < 0.11 studied by photoreflectance

Compressively strained Ge1-xSnx layers of various Sn content grown on Ge/Si templates have been studied by photoreflectance in 15-295 K temperature range. It has been confirmed that the direct optical transition between heavy-hole band and conduction band shifts to lower energy upon incorporation of Sn atoms. The shift of the transition energy in that temperature range has been found to be 68-91 meV which is slightly higher than the energy shift of direct transitions in Ge over the same temperature range. Varshni and Bose-Einstein coefficients for compressively strained Ge1-xSnx have been extracted from the analysis of the direct transitions and compared with parameters from literature. In addition the heavy-and light-hole related direct optical transitions in tensile strained Ge buffer layers have been measured and analyzed.