Metalorganic vapor phase epitaxy of pit-free AlN homoepitaxial films on various semipolar substrates

Abstract

Semipolar AlN homoepitaxial films, which are expected to act as underlying layers of highly efficient light emitters, are fabricated on 15°-off (0001), (11¯02), and (112¯2) AlN substrates using the metalorganic vapor phase epitaxy method. In conventional (0001) AlN growth, low reactor pressures are preferred to enhance the migration of Al adatoms and to suppress parasitic reactions between trimethylaluminum and ammonia. In contrast, low-pressure growth generates numerous pits on the surface of semipolar AlN grown homoepitaxially, which are derived from defects formed in the initial growth stage. Herein we experimentally demonstrate that higher-pressure growth can drastically decrease the pit density. A higher-pressure growth realizes atomically smooth surfaces, strong near-band-edge emissions with narrow line widths (∼1–2 meV), and well-suppressed deep level emissions. The optimal reactor pressure to eliminate pits is 500 Torr in terms of the growth rate and nucleation density.