Bound-double-exciton complexes in zinc-doped germanium

Photoluminescence from zinc-doped germanium is examined at liquid-helium temperatures. Three pairs of impurity-associated lines, in the set of phonon replicas, have been assigned to be radiations from single and double excitons bound to zinc, a double acceptor with deep levels. The dissociation energies of the bound exciton and the bound-double-exciton complex are 5.7 and 3.2 meV, respectively. The bound-double-exciton complex is very stable because of a closed-hole-shell structure.