Influence of AlN growth conditions on the polarity of GaN grown on AlN/Si(111) by metalorganic molecular beam epitaxy

We have investigated the influence of the growth conditions of AlN intermediate layers on the polarity of GaN layers grown on AlN/Si(111) by metalorganic molecular beam epitaxy (MOMBE). It was found from the results of co-axial impact collision ion scattering spectroscopy (CAICISS) that the polarity depended on the supply sequence of the source materials, AlN thickness and nitrogen source. When di-methyl-hydrazine (DMHy) was used as a N source, which was supplied before the Al source, N-polarity GaN became dominant. Even when the N source was supplied first, the Ga polarity became dominant when the thickness of AlN exceeded 45 nm. It was also found that when ammonia (NH3) was used as a N source, the Ga polarity became dominant even in N polarity AlN intermediate layers.