Electronic properties of a complex Cu-related acceptor with a bound exciton at 2.3423 eV in ZnTe.

Abstract

A detailed study of the electronic structure of a deep complex acceptor in ZnTe is reported, based on experimental data from optical spectroscopy of a corresponding bound exciton (BE) at 2.3423 eV (2 K). Only one electronic BE state is observed in the bandgap, quite unlike the situation with substitutional acceptors. From an evaluation of Zeeman data taken at 10 T for the BE line it is concluded that the hole in the neutral acceptor ground state, as well as the second hole in the BE two-hole state, are essentially spinlike, with a g value ${g}_{h}$ close to +2. The electron is shallow with an isotropic g value of ${g}_{e}$\ensuremath{\simeq}-0.40 and a quadratic Zeeman shift c\ensuremath{\simeq}7.5\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}6}$ eV/${\mathrm{T}}^{2}$, typical for shallow electron states in ZnTe. A residual anisotropic contribution of about 15% to the hole g value is observed, and explained as induced by the spin-orbit interaction for the bound hole. A realistic general description of magnetic properties of holes bound at complex acceptors is presented, without resort to the effective-mass formalism. The quenching of orbital angular momentum is observed for nondegenerate hole states in a strongly hole-attractive potential. A strong spin-orbit interaction may prevent such a quenching however, a quite common observation for other complex defects in ZnTe. The defect symmetry in this case is ${C}_{1h}$ from the Zeeman data, and the identity is tentatively suggested as a ${\mathrm{Si}}_{\mathrm{Te}}$-${\mathrm{Cu}}_{\mathrm{i}}$ pair. The axis is distorted about 8\ifmmode^\circ\else\textdegree\fi{} off the trigonal 〈111〉 direction, as a result of a relaxation of the ${\mathrm{Cu}}_{\mathrm{i}}$ interstitial ion towards one of the nearby Te atoms. Such a distorted configuration of the interstitial ion has recently been concluded also for other defects in ZnTe. The ionicity of ZnTe might be a sufficient reason for this relaxation of the ${\mathrm{Cu}}_{\mathrm{i}}$ interstitial ion.