Electrical transport and defect levels in ZnTe crystals

Two acceptor levels at 0.06 and 0.12–0.14 eV were observed in nominally pure ZnTe crystals using electrical transport measurements. Results on as-grown and annealed crystal show that these two levels are associated with different defect centers. It is suggested that neither level represents the first or second state of ionization of the native defect which dominates the electrical properties of pure ZnTe crystals at high temperatures. The deeper level appears to be associated with an impurity, possibly Cu. The identity of the shallow-level center is unknown; however, this center may be a complex center involving the native defect. Analysis of the temperature dependence of the hole mobility confirms that optical phonon scattering is dominant near room temperature in nominally pure ZnTe; however, ionized impurity scattering may become dominant at low temperatures.