High Quality Epitaxial Aluminum Nitride Layers on Sapphire by Pulsed Laser Deposition

We have grown high quality epitaxial AlN layers on sapphire substrates by pulsed laser ablation of a stoichiometric AlN target. The AlN films deposited at 800 °C and laser energy densities in the range of 2–3 J/cm² were found to be epitaxial with the c axis normal to the Al2O3 surface. The x‐ray rocking curve of epitaxial AlN films yielded a full width at half maximum of 0.21°. The selected area electron diffraction patterns and high resolution transmission electron microscopy also revealed that the films were epitaxial with an orientational relationship of AlN‖Al2O3 and in‐plain alignment of AlN‖Al2O3 and AlN‖Al2O3. This is equivalent to 30° rotation in the basal plane of the AlN film with respect to the sapphire substrate.

The absorption edge measured by ultraviolet‐visible spectroscopy for the epitaxial AlN film was sharp and the band gap was found to be 6.1 eV. The electrical resistivity of the films was about 5–6×1013 ohm cm with a breakdown field of 5×106 V/cm. At higher laser energy densities ≥10 J/cm2 and lower temperatures ≤650 °C, the deposited films were nitrogen deficient and contained free metallic aluminum, both of which degrade the microstructural, electrical, and optical properties of the AlN films.


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