Isotope dependence of the indirect energy gap of germanium

Abstract

No-phonon luminescence from excitons bound to shallow donors and acceptors in crystalline germanium is found to move to higher energy with increasing mass number A of the germanium at the rate dE/dA=0.35+or-0.02 meV. The authors show that it is possible to predict this shift, to a good approximation, from the temperature dependence of the energy gap and the effect on the lattice parameter of the different isotopes.