Controlled oxygen doping of GaN using plasma assisted molecular-beam epitaxy

High-quality (0001) and (0001̄)-GaN films were grown by plasma-assisted molecular-beam epitaxy to study the dependence of oxygen incorporation on polarity and oxygen partial pressure. Oxygen incorporates at a rate ten times faster on nitrogen-polar GaN than on the Ga polarity. Oxygen doping is controllable, reproducible, and produces low compensation material up to concentrations of at least ${10}^{18} {\mathrm{cm}}^{\mathrm{-3}}$ with higher levels showing significant compensation. Layers containing oxygen at levels above ${10}^{22} {\mathrm{cm}}^{\mathrm{-3}}$ exhibit severe cracking while oxygen concentrations less than ${10}^{21} {\mathrm{cm}}^{\mathrm{-3}}$ do not introduce significant strain. The oxygen incorporation rate has a weak dependence on Ga overpressure during Ga-stable growth but dramatically increases for conditions approaching N-stable growth.