Effect of Temperature and Doping on the Reflectivity of Germanium in the Fundamental Absorption Region

The 2.1- and 4.4-ev peaks in the reflectivity spectrum of germanium have been studied as a function of temperature and doping. The temperature coefficient of the 2.1-ev peak is -4.2×{}10^-4 ev/^∘{}K, that of the 4.4-ev peak -1.8×{}10^-4 ev/^∘{}K. Large donor concentrations give a decrease in the energy gap at the zone boundary in the [111] direction which is nearly the same as the shrinkage of the thermal gap. No shift with doping of the 4.4-ev peak was detected. The spin-orbit splitting of the valence band at the L₃^' point in the zone boundary was found to be 0.18 ev.