Channeling study of thermal decomposition of III-N compound semiconductors

Abstract

GaN thermal stability is the limiting factor of the growth rate for epitaxially grown films and of the thermal annealing of defects. As a consequence, this issue has been extensively studied for more than one decade. There are, however, substantial differences in the reported kinetics and presumed mechanisms of decomposition, which are primarily related to the reactor design thus, reflecting the complexity of chemical reactions involved. We report here on the use of 1.7MeV He-ion RBS/channeling for the study of thermal decomposition of MOVPE grown GaN and AlxGa1−xN (x=0.05–0.5) layers. These layers with thickness of 320nm were grown on sapphire substrates with 20nm AlN nucleation layer. Prior to annealing samples were characterized by RBS/channeling, selected samples were also studied by SEM. Thermal treatment was performed in the MOVPE reactor in the temperature range 900–1200°C in the N2 atmosphere. RBS/channeling analysis provided data on layer thickness, composition and evolution of ingrown defects. GaN decomposition starts at 900°C and results in the reduction of the layer thickness without observable changes of the film composition. The presence of large density of GaN hillocks on the surface was revealed by SEM after annealing at 1000–1050°C. Remarkable stability of AlxGa1−xN was observed, this alloy remains unchanged upon annealing at 1200°C/6h even for x as low as 0.05.