The formation energy and charge states of substitutional and interstitial C impurities and their complexes in ZnO were studied using density functional theory calculations. While single CZn defects had the highest absolute stability, interstitial C in n-type ZnO prefers to form interstitial C2 pairs or CZn–Ci complexes, thereby lowering the defect formation energy. Moreover, those atomic C impurities that had low formation energy were found to be nonmagnetic in their stable charge states. However, both in p-type and n-type ZnO, certain charge states of C2 complexes possessing a spin magnetic moment were identified. This might give a clue why both p-type and n-type magnetism were reported for C-doped ZnO samples.
Density Functional Study of Carbon Doping in ZnO. S.Sakong, P.Kratzer: Semiconductor Science and Technology, 2011, 26, 014038