Vanadium centers in ZnTe crystals. II. Electron paramagnetic resonance.

Abstract

Four V-related electron-paramagnetic-resonance (EPR) spectra are observed in Bridgman-grown ZnTe doped with vanadium. Two of them are attributed to the charge states ${{\mathrm{V}}_{\mathrm{Zn}}}^{3+}({A}^{+})$ and ${{\mathrm{V}}_{\mathrm{Zn}}}^{2+}({A}^{0})$ of the isolated V impurity. For the ionized donor, ${{\mathrm{V}}_{\mathrm{Zn}}}^{3+}({A}^{+})$, the spectrum reveals the typical behavior of the expected $^{3}A_{2}(F)$ ground state in tetrahedral symmetry. The incorporation on a cation lattice site could be proved by the resolved superhyperfine interaction with four Te ions. The second spectrum showing triclinic symmetry and $S=\frac{3}{2}$ is interpreted as the neutral donor state ${{\mathrm{V}}_{\mathrm{Zn}}}^{2+}({A}^{0})$. The origin of the triclinic distortion of the cubic (${T}_{d}$) crystal field could be a static Jahn-Teller effect. The two additionally observed EPR spectra are attributed to nearest-neighbor V-related defect pairs. The spectrum of the first one, ${\mathrm{V}}_{\mathrm{Zn}}^{2+}$-${Y}_{\mathrm{Te}}$, shows trigonal symmetry and can be explained by the $S=\frac{3}{2}$ manifold of an orbital singlet ground state. An associated defect ${Y}_{\mathrm{Te}}$ is responsible for the trigonal distortion of the tetrahedral crystal field of ${\mathrm{V}}_{\mathrm{Zn}}^{2+}$. The spectrum of the second pair defect also shows trigonal symmetry and can be described by $S=\frac{1}{2}$. The ground-state manifold implies a ${{V}_{\mathrm{Zn}}}^{3+}\ensuremath{-}{X}_{\mathrm{Te}}$ pair as the most probable origin of this spectrum. The $S=\frac{1}{2}$ ground state is produced by a dominating isotropic exchange interaction coupling the $S=1$ ground-state manifold of ${\mathrm{V}}_{\mathrm{Zn}}^{3+}$ to an assumed $S=\frac{1}{2}$ ground state of ${X}_{\mathrm{Te}}$ in antiferromagnetic orientation. The nature of the associated defects ${Y}_{\mathrm{Te}}$ and ${X}_{\mathrm{Te}}$ remains unknown for both pairs since no hyperfine structure has been observed, but most probably acceptorlike defects are involved.