Stress evolution in AlN layers grown on c-Al2O3 by plasma-assisted molecular beam epitaxy at metal-rich conditions

Abstract

Stress generation and relaxation in AlN nucleation and buffer layers grown on c-Al2O3 substrates by plasma-assisted molecular beam epitaxy at low (LT, TS = 780°C) and high (HT, TS = 850°C) substrate temperatures were studied. Oscillation behavior of the wafer curvature (stress×thickness) was revealed during pulsed deposition of AlN in metal modulated epitaxy and migration enhanced epitaxy modes under the metal-rich conditions, which corresponded to Al bilayer formation and consumption. Minimal average stress ∼ +0.05 GPa in AlN buffer layers was observed at LT growth, which increased up to +0.85 GPa at HT growth. In addition, the LT AlN layers demonstrated lower densities of screw and edge threading dislocations equal to 7.8·108, 5.1·109 cm−2, respectively, while in the case of HT AlN layers those densities were significantly higher.