Microstructural assessment of InN-on-GaN films grown by plasma-assisted MBE

The structural properties of InN thin films, grown by rf plasma-assisted molecular beam epitaxy on Ga-face GaN/Al2O3(0001) substrates, were investigated by means of conventional and high resolution electron microscopy. Our observations showed that a uniform InN film of total thickness up to 1 mum could be readily grown on GaN without any indication of columnar growth. A clear epitaxial orientation relationship of [000l]GaN parallel to [0001]InN, (1010)GaN parallel to (1010)InN was determined. The quality of the InN film was rather good, having threading dislocations as the dominant structural defect with a density in the range of 10(9)-10(10) cm(-2). The crystal lattice parameters of wurtzite InN were estimated by electron diffraction analysis to be a = 0.354 nm and c = 0.569 nm, using Al2O3 as the reference crystal. Heteroepitaxial growth of InN on GaN was accomplished by the introduction of a network of three regularly spaced misfit dislocation arrays at the atomically flat interface plane. The experimentally measured distance of misfit dislocations was 2.72 nm. This is in good agreement with the theoretical value derived from the in-plane lattice mismatch of InN and GaN, which indicated that nearly full relaxation of the interfacial strain between the two crystal lattices was achieved. (C) 2004 Elsevier Ltd. All rights reserved.