High resistivity In-doped ZnTe: electrical and optical properties

Semi-insulating < 111 > ZnTe prepared by In doping during Bridgman growth was found to have a resistivity of 5(.)74 x 10(7) ohm-cm, the highest reported so far in ZnTe, with hole concentration of 2(.)4 x 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 degrees 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.