Dependence of Al incorporation on growth temperature during laser molecular beam epitaxy of AlxGa1−xN epitaxial layers on sapphire (0001)

We report the successful growth of AlxGa1−xN (0 ≤ x ≤ 0.25) epitaxial films on c-plane sapphire substrate by using laser molecular beam epitaxy technique. The role of growth temperature on the Al incorporation and the structural, electronic and optical properties of the AlxGa1−xN epitaxial layers grown in the temperature range 500-700 °C have been systematically studied. The atomic force microscopy analysis shows that the grain size of AlxGa1−xN increases with increase in growth temperature and flat surface epilayers are obtained at ≥ 600 °C. The Al incorporation is confirmed with high resolution x-ray diffraction, x-ray photo electron microscopy and photoluminescence studies. It is observed that the growth temperature plays a critical role in determining the Al composition, which increases with increasing growth temperature. AlxGa1−xN layer with about 23% of Al composition is obtained on sapphire (0001) substrate at a growth temperature of 700 °C, which is about 100-150 °C lower than the conventional molecular beam epitaxy growth.