Possible identification of zinc-vacancy–donor-impurity complexes in zinc telluride by optically detected magnetic resonance

Application of the optically detected magnetic resonance (ODMR) technique to donor-acceptor recombination luminescence in donor-doped ZnTe crystals shows the presence of two acceptor centers having noncubic symmetry. One of these centers, labeled Aₜ, has precisely trigonal symmetry C₃. In terms of a spin Hamiltonian for an effective spin S=1/2, its g factors are gzz=2.664 and gₓₓ=gyy{}0, where z corresponds to a 〈111〉 direction. The other center, labeled Aₘ, has mirror symmetry CS, with gzz=2.540 and gₓₓ{}gyy{}0.25, where the z axis is inclined at 6.7^∘{} to 〈111〉 in a {110} plane. The g factors are interpreted by considering the effect of a low-symmetry crystal field on a J=(3/2) (Γ₈) hole in ZnTe.Hyperfine splittings of magnitude 190×{}10^-4 cm^-1 for Aₜ and 180×{}10^-4 cm^-1 for Aₘ are observed in the ODMR spectra and attributed to interactions with three equivalent or nearly equivalent Te nuclei. Center Aₜ is observed in chlorine-doped ZnTe; center Aₘ is observed in aluminum-doped ZnTe and is very likely the acceptor called AC, known by its bound-exciton line at 2.369 eV. It is proposed that these single-acceptor centers are double-acceptor--single-donor pairs and, more precisely, that the double-acceptor constituent is the zinc vacancy. That is, the trigonal center Aₜ is V_ZnClTe and the mirror-symmetry center Aₘ is V_ZnAlZn. If this interpretation is correct, the electronic properties of vacancy centers in ZnTe are remarkably different from those of the well-known VZn--donor-impurity associates (the ``A centers'') in ZnSe and ZnS. Whereas the latter centers are very deep centers with large pseudo-Jahn-Teller distortions, centers Aₜ and Aₘ in ZnTe are of shallow or intermediate depth, retain the full symmetry of the vacancy-impurity complex, and have unquenched orbital angular momentum. Finally, it is suggested that the detection of zinc-vacancy acceptors in donor-doped ZnTe may help one to understand the difficulty of producing n-type material.