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

We report the synthesis of 1 mu m thick single crystalline aluminum nitride films by dc magnetron sputtering on AlGaN/GaN layer grown on sapphire substrate at low temperature (substrate temperature 250 degrees 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 (20-30 eV) during the growth, leads to an increase in the surface mobility and thus promotes AlN epitaxial growth on AlGaN substrate at 250 degrees C.