ABSTRACTWe report on a comparative study of the growth of GaN in an arsenic free MBE system using either the method of plasma activation of molecular nitrogen or catalytic decomposition of ammonia on a heated substrate. We find that while growth with a plasma source leads to smooth films only under Ga- rich conditions, growth with ammonia leads to smooth films under ammonia-rich conditions. In both cases we find a 2×2 surface reconstruction when using an AlN buffer, which is evidence that material grown with this buffer layer has the Ga-polarity. In the case of plasma growth we also investigated the use of a GaNbuffer and found that at the growth temperature the surface is unreconstructed, however it undergoes 3×3 reconstruction upon cooling to 300 °C. This observation is evidence that material grown on a GaN buffer has the N-polarity.
