We have investigated the effect of annealing in an O2 atmosphere on the electrical properties of high-quality ZnO single crystals grown by seeded chemical vapor transport (SCVT). A temperature dependent Hall-effect technique indicates that the dominant donor in as-grown ZnO crystals has an ED of 42.8 meV and ND value of 2.8 × 1017 cm−3. After heat treatment in the O2 atmosphere at 1000 oC for 5 h, the color of the crystal changed from an orange color to transparent, and the ND value decreased to 4.3 × 1016 cm−3, while the ED value did not change. It can be deduced that the dominant donor in as-grown ZnO single crystals is a donor type native defect, which has a donor binding energy of about 42.8 meV.

Keywords: II-VI semiconductors, Hall measurements, Donor binding energy, Zinc oxide.