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

Compressively strained Ge1−x Sn x 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−x Sn x 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.