Pair Spectra and the Shallow Acceptors in ZnSe

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 28 meV. Under conditions of weak excitation, the distant pair band peaks at an energy of 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 Li^6 isotope proves that the acceptor is substitutional Li, with a binding energy E₀=1142 meV. A second shallow acceptor, tentatively assigned to Na, has E₀90-100 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.