Semi-polar (11–22) AlN epitaxial films on m-plane sapphire substrates with greatly improved crystalline quality obtained by high-temperature annealing

Abstract

This study addresses the difficulty of obtaining relatively low-cost semi-polar (11–22) AlN films epitaxially grown on m-plane sapphire substrates with high crystalline quality by applying a cost-effective high-temperature annealing process conducted at 1700 °C to films grown via standard-temperature metal organic chemical vapor deposition. The X-ray diffraction rocking curves of the annealed films along the [11–23] and [10–10] directions obtain full width at half maximum values of 0.152° and 0.193°, respectively. Atomic force microscopy results demonstrate the occurrence of a significant recrystallization process in the columnar formations of AlN films during annealing, resulting in increased AlN crystal grain size. Raman spectroscopy measurements reveal that the semi-polar (11–22) AlN films are subject to increased compressive stress after the annealing process. Transmission electron microscopy analyses confirm that our semi-polar AlN films provide appropriately low dislocation and basal stacking fault densities of 5.6 × 109 cm−2 and 1.05 × 105 cm−1, respectively. The proposed approach therefore obtains low-cost AlN films that are suitable for the mass manufacture of efficient optoelectronic devices.