Investigation of Si-doping and Impurity Incorporation Dependence on the Polarity of GaN by MBE

We have investigated the growth of Ga-polarity (0001) and N- polarity (000?1) Si-doped GaN on c-plane sapphire substrates by plasma-assisted Molecular Beam Epitaxy (MBE). For a given Si effusion cell temperature and under similar growth conditions, the Hall carrier concentration was found to be consistently higher for samples with N-polarity. Secondary ion mass spectrometry measurements show no significant difference for the incorporation of Si into GaN of either polarity. However, the incorporation of background impurities, C and O, was found to be higher for the (000?1) GaN samples.