Epitaxial growth of aluminum nitride on AlGaN by reactive sputtering at low temperature

We report the synthesis of 1μm thick single crystalline aluminum nitride films by dc magnetron sputtering on AlGaN∕GaN layer grown on sapphire substrate at low temperature (substrate temperature <250°C). The microstructure of c-axis oriented AlN films deposited on Si (100) and AlGaN ⟨0001⟩ substrates was studied by x-ray diffraction, selected area electron diffraction, and transmission electron microscopy. The optimization of process parameters, involving low energetic ion bombardment on film surface (20–30eV) during the growth, leads to an increase in the surface mobility and thus promotes AlN epitaxial growth on AlGaN substrate at 250°C.