Growth morphology and surface-acoustic-wave measurements of AIN films on sapphire

Aluminum nitride epitaxial films of thicknesses greater than 10 μ with excellent mechanical and chemical stability have been grown on R-plane sapphire substrates. The orientation relationship of single-crystal AlN on sapphire is discussed. Examination of the as-grown AlN film surface with a scanning electron microscope identifies the growth morphology and enables differentiation between good and poor quality films. The surface-acoustic-wave coupling constant K ² and propagation velocity V_s are measured out to a thickness-to-wavelength ratio t/λ=0.75 with typical K² values of 0.8% and V_s of 6.1 km/sec. Preliminary results also indicate that AlN-sapphire interfacial strain extends about 1 μ into the AlN film.