High resistivity In-doped ZnTe: electrical and optical properties

Semi-insulating ZnTe prepared by In doping during Bridgman growth was found to have a resistivity of 5 ·74 × 10 7 ohm-cm, the highest reported so far in ZnTe, with hole concentration of 2 ·4 × 10 9 /cm 3 and hole mobility of 46 cm 2 /V·s at 300 K. The optical band gap was 2·06 eV at 293 K compared with 2·26 eV for undoped semiconducting ZnTe. Thermally stimulated current (TSC) studies revealed 2 trap levels at depths of 202 -222 meV and 412-419 meV, respectively. Photoluminescence (PL) studies at 10 K showed strong peaks at 1 ·37 eV and 1·03 eV with a weak shoulder at 1 ·43 eV. Short anneal for 3 min at 250°C led to conversion to a p-type material with resistivity, 14 ·5 ohm -cm, indicating metastable behaviour. Raman studies carried out on undoped and In-doped samples showed small but significant differences. Possible models for semi-insulating behaviour and meta-stability are proposed.