Synthesis of AlN Thin Films on Sapphire Substrates by Chemical Vapor Deposition of AlCl3–NH3 System and Surface Acoustic Wave Properties

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Abstract
Thin films of AlN were prepared on (012) sapphire substrates by chemical vapor deposition using AlCl3, NH3, H2 and N2 gases. Crystal orientations, surface microstructures, oxygen impurity contents of the films and surface acoustic wave (SAW) properties determined using an interdigital transducer were investigated. Under optimized conditions, epitaxial AlN films were deposited and crystal orientation of AlN films increased as the thickness of the films increased. Oxygen impurity contents were less than 1 atm%. The dependence of SAW velocity along the [001] AlN axis on the film thickness was in good agreement with the theoretical prediction and the temperature coefficients of the center frequency increased as the film thickness increased. These tendencies are considered to be explained by the high crystal orientation and low oxygen impurity content of AlN epitaxial films.