Pair Spectra and the Shallow Acceptors in ZnSe

Abstract

Donor-acceptor pairs associated with the three effective-mass-like donors Al, Ga, and In have been observed in the photoluminescence spectra of ZnSe. The previously determined binding energies of these donors are $\ensuremath{\sim}$ 28 meV. Under conditions of weak excitation, the distant pair band peaks at an energy of $\ensuremath{\sim}$ 2.69 eV. The identification of discrete pair lines indicates that both the donor and acceptor are on the same sublattice. The shift of all pair lines by 0.05-0.1 meV to lower energy when crystals are doped with the ${\mathrm{Li}}^{6}$ isotope proves that the acceptor is substitutional Li, with a binding energy ${E}_{A}=114\ifmmode\pm\else\textpm\fi{}2$ meV. A second shallow acceptor, tentatively assigned to Na, has ${E}_{A}\ensuremath{\sim}90\ensuremath{-}100$ meV, estimated from the corresponding bound-exciton line. Another more complex pair spectrum is reexamined. The discrete pair lines for this system exhibit a doubling of all lines, but the chemical identity of the donor and acceptor producing this spectrum remains undetermined.