Electronic properties of a shallow complex acceptor in CdTe

A shallow complex acceptor in CdTe with a binding energy of 56.4\ifmmode\pm\else\textpm\fi{}0.5 meV is reported. A bound-exciton (BE) line at 1.5901 eV is found to be associated with this acceptor, the most shallow acceptor-related bound exciton discovered so far in CdTe. Two-hole photoluminescence satellites recorded with resonant excitation in the 1.5901-eV bound-exciton line reveal several s-like excited states of the acceptor hole, of which the 2S replica interacts strongly with phonons in the range of the two-${\mathrm{LO}}^{\mathrm{\ensuremath{\Gamma}}}$-phonon mode. A complicated phonon spectrum in the optical-phonon range is found for this bound exciton. Further, the two-hole spectrum contains additional electronic lines, not seen for substitutional acceptors in tetrahedral symmetry. Two such lines, corresponding to hole energies 7.3 and 33.3 meV above the acceptor ground state, are interpreted as excited states associated with the component of the ${\ensuremath{\Gamma}}_{8}$ hole state split by the local strain field, and the 2${P}_{3/2}$ excited hole state, respectively. Dye-laser-excited photoluminescence excitation spectra similarly reveal excited states to the bound exciton, particularly a doublet at \ensuremath{\approxeq}2.6 meV above the 1.5901-eV lowest BE state. These excited BE states are interpreted as states split off from the lowest at 1.5901 eV by the local axial strain field at the defect.