Influence of the N2/H2 ratio on the structural features of InxGa1−xN/GaN films grown by MOCVD

The influence of the N2/H2 ratio in the growth environment on the defect structures of InGaN films was investigated by means of transmission electron microscopy and atomic force microscopy. InxGa1−xN films (100 nm thick) were grown by MOCVD on GaN/Al2O3 (0001) epilayers. In one case, the InGaN film was grown in pure H2 carrier gas whereas, in the other, a N2+H2 mixture with a N2/H2 ratio of 4 was used. The actual indium incorporation in the InxGa1−xN epitaxial layers strongly depends on N2/H2 ratio. The surfaces of both InGaN films exhibit a high density (∼109 cm−2) of hexagonal shaped pits with a diameter of the order of a few tens of nanometres. The defect structures observed in the samples are the same and seem to be mainly dislocations and inversion domains, which terminate on the film surface with inverted hexagonal pyramids which are defined by six planes.