Origins of Electrical Compensation in Si-Doped HVPE GaN

Herein, the results of positron lifetime and X-ray absorption spectroscopy obtained in Si-doped GaN crystals, grown by the hydride vapor phase epitaxy (HVPE), are reported. Pushing the Si doping to high concentrations leads to surprisingly strong compensation effects. Positron experiments show that the concentrations of Ga vacancies are not high enough to be efficient compensation centers. Other acceptor-like impurities are present in concentrations orders of magnitude lower than the Si content in the samples. X-ray absorption shows that the local environment of Si dopants in compensated samples is different from the fully activated case. Simulated spectra of X-ray absorption near edge structure strongly suggest that in compensated spectra Si is likely to have more Si atoms in the nearest local environment. Hence, autocompensation of Si dopants appears as a likely compensation mechanism at high Si contents GaN samples grown by HVPE.