Photoluminescence from excitons bound to a triple acceptor, Ge:Cu

Abstract
We report the first observation of a triple-acceptor bound exciton, revealed in the photoluminescence spectrum of Cu-doped Ge, and verified by a two-hole replica series having the known Cu ionization energy. High-resolution photoluminescence reveals a finely split doublet independent of Cu isotopic species. This is an unexpected result, since present models of both the triple acceptor and its bound exciton predict that neither ground state should have any fine structure.