Growth Optimization of Nonpolar Al0.7Sc0.3N(112 over bar 0)/Al2O3(11 over bar 02) Thin Films Using Reactive Magnetron Sputter Epitaxy

A-plane Al0.7Sc0.3N(112 over bar 0) thin films are grown on r-plane Al2O3(11 over bar 02) substrates using reactive pulsed-DC magnetron sputter epitaxy. This is the first report of successful synthesis of nonpolar epitaxial AlScN films with a high scandium concentration (30%). The influence of different sputtering conditions, such as magnetron power, temperature, and process gas flow rates, is investigated. The film characteristics are also compared on different substrate offcuts. Controlling the diffusion of adatoms on surface of the substrate is found to have the highest influence on film quality. The X-ray diffraction measurements confirm in-plane oriented AlScN(112 over bar 0) layers and the final optimized films show significant improvement in rocking curve full width at half maximum (omega-FWHM) of 112 over bar 0 reflection. Corresponding atomic force microscopy (AFM) measurements show mean root square surface roughness (R-q < 0.4 nm) nearing atomically smooth levels. The optimized films also exhibit anisotropic growth characteristics. A growth model for a-plane AlScN has been proposed based on the growth parameters of the film.