AlGaN films grown on (0001) sapphire by a two-step method

A two-step growth method, commonly used for GaN on sapphire, was applied to grow high-quality Al0.2 Ga0.8 N on sapphire. Comparing to the one grown on a low-temperature grown AlN buffer layer, the decomposition, recrystallization, and islands coalescence processes of the two-step growth increased the surface flatness, the crystal quality, the electrical property, suppressed the phase separation, and released the biaxial tensile strain. A 2.0 μm thick high-quality crack-free nearly GaN-free Al0.2 Ga0.8 N epilayer was obtained.