Carbon-Based Defects in GaN: Doping Behaviour

We present first-principles calculations for the substitutional carbon impurity on the nitrogen and gallium sites, and substitutional and split-interstitial dicarbon pairs (2C) in cubic GaN. The pseu-dopotential approach and a plane-wave expansion are applied in the framework of density func-tional theory (DFT) and local density approximation (LDA). The stability of carbon-based defects versus the Fermi level and preparation conditions is analysed. Calculations taking into account several impurities and native defects in their charge states are performed in order to determine the defect which is formed at the highest concentration. The results provide information about consequences of carbon doping in cubic GaN. They are used to elucidate the compensation mechanism seemingly observed with the increment of the high carbon concentrations in recent experiments. Introduction Recent developments in group-III nitrides have resulted in successful fabrication of optical devices based on GaN. The quality of the devices relies in part on the control of doping properties. Magnesium has been traditionally used to obtain p-type doping in GaN, but it has some disadvantages such as high vapour pressure, tendency to segregation, migration on the growing surface, and low ionization ratio a