Density functional study of carbon doping in ZnO
The formation energy and charge states of substitutional and interstitial C impurities and their complexes in ZnO have been studied using density functional theory calculations. While single C_Zn defects have the highest absolute stability, interstitial C in n-type ZnO prefers to form interstitial C_2 pairs or C_Zn–Ci complexes, thereby lowering the defect formation energy. Moreover, those atomic C impurities that have low formation energy are found to be nonmagnetic in their stable charge states. However, both in p-type and n-type ZnO, certain charge states of C_2 complexes possessing a spin magnetic moment are identified. This might give a clue why both p-type and n-type magnetism have been reported for C-doped ZnO samples.
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