Room-temperature heteroepitaxy of single-phase Al_(1-x)In_xN films with full composition range on isostructural wurtzite templates

摘要

Al_(1-x)In_xN heteroepitaxial layers covering the full composition range have been realized by magnetron sputter epitaxy on basal-plane A1N, GaN, and ZnO templates at room temperature (RT). Both Al_(1-x)In_xN single layers and multilayers grown on these isostructural templates show single phase, single crystal wurtzite structure. Even at large lattice mismatch between the film and the template, for instance InN/AIN (～13% mismatch), heteroepitaxy is achieved. However, RT-grown Al_(1-x)In_xN films directly deposited on non-isostructural c-plane sapphire substrate exhibit a polycrystalline structure for all compositions, suggesting that substrate surface structure is important for guiding the initial nucleation. Degradation of Al_(1-x)In_xN structural quality with increasing indium content is attributed to the formation of more point- and structural defects. The defects result in a prominent hydrostatic tensile stress component, in addition to the biaxial stress component introduced by lattice mismatch, in all RT-grown Al_(1-x)In_xN films. These effects are reflected in the measured in-plane and out-of-plane strains. The effect of hydrostatic stress is negligible compared to the effects of lattice mismatch in high-temperature grown A1N layers thanks to their low amount of defects. We found that Vegard's rule is applicable to determine x in the RT-grown Al_(1-x)In_xN epilayers if the lattice constants of RT-sputtered A1N and InN films are used instead of those of the strain-free bulk materials.