Compensation in Be-doped Gallium Nitride Grown Using Molecular Beam Epitaxy

Three techniques to improve beryllium doping in Ga-polar GaN grown by molecular beam epitaxy were investigated: growth under atomic hydrogen, growth under electron irradiation, and growth under an In flux. The samples were characterized by photoluminescence and Hall effect measurements. None of these approaches led to enhanced Be activation. Optical evidence that the Be activation energy may be about 190 meV is presented. Selected samples were also characterized using positron annihilation spectroscopy in an attempt to correlate compensation and PL features with microscopic defects. Positron annihilation spectroscopy (PAS) studies suggest that gallium vacancies and/or gallium vacancy complexes may be related to compensation in beryllium doped gallium nitride samples. There is a correlation between donor-acceptor pair photoluminescence at 3.38eV, beryllium concentration, and yellow-red photoluminescence at 2.0 to 2.1eV.