Piezospectroscopic study of Be double acceptors in Ge

Under uniaxial stress the single-hole (1s${)}^2$→(1s)(np) excitation spectrum of Ge(${\mathrm{Be}}^0$) shows splittings and polarization effects. These piezospectroscopic effects were observed for a compressive force F along [111] and along [100]. They are interpreted in terms of $T_d$ site symmetry for the substitutional Be acceptors when unstressed and a deformation-potential theory in which the phenomenological deformation-potential constants characterizing the single-hole states determine the behavior of the (1s${)}^2$ as well as the (1s)(np) levels. The shear-deformation-potential constants have been deduced for the ground state and the excited state of the D transition. Pronounced level-crossing effects in the intensities of the stress-induced components of the G transition are observed.