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. 210^-4 ev/^, that of the 4. 4-ev peak -1. 810^-4 ev/^. 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.