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

Abstract
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 K2 and propagation velocity Vs are measured out to a thickness‐to‐wavelength ratio t/λ=0.75 with typical K2 values of 0.8% and Vs of 6.1 km/sec. Preliminary results also indicate that AlN‐sapphire interfacial strain extends about 1 μ into the AlN film.

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