Dependence of carbon doping concentration on the strain-state and properties of GaN grown on Si substrate

Dependence of carbon doping concentration on the strain-state and properties was studied in detail for the GaN on Si system. Combining the results of XRD and Raman spectra, it is found that compressive stress is introduced into the GaN with a moderate carbon concentration, while it turns into tensile stress when the carbon concentration is higher than a critical point. A possible mechanism is that the carbon tend to replace the N atom in GaN at a relative lower carbon concentration because of the relatively smaller formation energy, while it turned to replace the Ga atom after the carbon concentration is higher than a critical level. Those results are also confirmed by the photoluminescence spectrum.