Pair Spectra and "Edge Emission" in Zinc Selenide

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Abstract
We have observed a large number of sharp lines in photoluminescence spectra of ZnSe at 4.2°K, leading to a broad band at lower energy. The peak energy of this band increases from ∼2.70 to ∼2.72 eV with large increase in excitation intensity. The energies and intensities of the sharp lines are consistent with recombinations between distant donor-acceptor pairs. This is the first report of such a spectrum from a II-VI compound or any direct gap semiconductor. Two high-energy pair spectra (HEPS) occur with similar patterns of sharp lines mutually displaced by 2.0±0.2 meV. A lower-energy pair spectrum (LEPS), with peak near 2.69 eV, also often occurs in ZnSe. Sharp lines have not been resolved in the LEPS. A high-energy series of broad bands, whose properties suggest free-to-bound recombinations, is readily seen in association with the LEPS, but not with the HEPS. The thermal-quenching rate is greater for the LEPS than for the HEPS. This difference in behavior can be understood if the donor and acceptor in the HEPS have comparable ionization energies, while these energies differ considerably in the LEPS. The identities of the donors and acceptors are unknown.

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