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

Abstract

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 ${A}_{t}$, has precisely trigonal symmetry ${C}_{3}$. In terms of a spin Hamiltonian for an effective spin S=1/2, its g factors are ${g}_{\mathrm{zz}}$=2.664 and ${g}_{\mathrm{xx}}$=${g}_{\mathrm{yy}}$\ensuremath{\simeq}0, where z corresponds to a 〈111〉 direction. The other center, labeled ${A}_{m}$, has mirror symmetry ${C}_{S}$, with ${g}_{\mathrm{zz}}$=2.540 and ${g}_{\mathrm{xx}}$\ensuremath{\simeq}${g}_{\mathrm{yy}}$\ensuremath{\simeq}0.25, where the z axis is inclined at 6.7\ifmmode^\circ\else\textdegree\fi{} 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) (${\ensuremath{\Gamma}}_{8}$) hole in ZnTe.Hyperfine splittings of magnitude 190\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ for ${A}_{t}$ and 180\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}4}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ for ${A}_{m}$ are observed in the ODMR spectra and attributed to interactions with three equivalent or nearly equivalent Te nuclei. Center ${A}_{t}$ is observed in chlorine-doped ZnTe; center ${A}_{m}$ is observed in aluminum-doped ZnTe and is very likely the acceptor called ${A}_{C}$, 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 ${A}_{t}$ is ${V}_{\mathrm{Zn}{\mathrm{Cl}}_{\mathrm{Te}}}$ and the mirror-symmetry center ${A}_{m}$ is ${V}_{\mathrm{Zn}{\mathrm{Al}}_{\mathrm{Zn}}}$. If this interpretation is correct, the electronic properties of vacancy centers in ZnTe are remarkably different from those of the well-known ${V}_{\mathrm{Zn}--}$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 ${A}_{t}$ and ${A}_{m}$ 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.