Structural properties of InN films grown on sapphire substrates by microwave-excited metalorganic vapor-phase epitaxy

The structural properties of InN films grown on (0001) sapphire (α-Al2O3) substrates are investigated by reflection high-energy electron-diffraction and x-ray-diffraction methods. The epitaxial relationship between the InN layer and the α-Al2O3 substrate is revealed to be (0001)InN //(0001)α-Al2O3 with [101̄0]InN//[101̄0] α-Al2O3, which is different from that of AlN and GaN epitaxial films. The x-ray rocking curve measurements prove that the crystalline quality of as-grown InN films is not so good, while it can be significantly improved by thermal annealing at temperatures of 450–500 °C within 10 min in nitrogen ambient. The improvement of quality is ascribed to the rearrangement of mosaic crystallites in the films through the movement of their boundaries during a short period of time.