Structural characterization of AlN (11-22) films prepared by sputtering and thermal annealing on m-plane sapphire substrates

(11-22)-oriented AlN films are sputtered on m-plane sapphire substrates at different temperatures. With an optimized sputtering temperature of 800 degrees C and high-temperature annealing at 1600 degrees C, the full widths at half maximum (FWHMs) of X-ray diffraction of AlN are 0.186 degrees and 0.243 degrees along [11-23] AlN and [1-100](AlN). The annealed AlN shows smooth surface morphology with a roughness of 0.425 nm. Convergent beam electron diffraction patterns display that the annealed AlN (11-22) film is grown with Al-face sense polarity rather than mixed polarity in c-plane sputtered AlN, which may result from less oxygen in the AlN/sapphire interface. Threading dislocations with a density of 7.5 x 10(9) cm(-2) and stacking faults with a density of 1.1 x 10(5) cm(-1) are identified in the transmission electron microscopy cross-sectional images. The crystal quality of AlN in this work is attractive for growth and fabrication of AlN or AlGaN-based semipolar devices.