Intrinsic Optical Absorption in Single-Crystal Germanium and Silicon at 77°K and 300°K

The intrinsic absorption spectra of high-purity single-crystal germanium and silicon have been measured at 77^ and 300^. The spectral regions studied encompassed a range of absorption coefficient from 0. 1 cm^-1 to 10^5 cm^-1 for each material. The germanium data may be interpreted as indicating a threshold for direct transitions at 0. 81 ev at 300^ and at 0. 88 ev at 77^. The threshold for indirect transitions was placed at 0. 62 ev and 0. 72 ev for 300^ and 77^, respectively. For silicon the data were not as readily interpreted However, there is an indication that the threshold for direct transitions should be placed at about 2. 5 ev and the threshold for indirect transitions at 1. 06 ev and 1. 16 ev at 300^ and 77^, respectively.