Progress in high crystalline quality AlN grown on sapphire for high-efficiency deep ultraviolet light-emitting diodes

Abstract

AlGaN with a high Al fraction and low-dimensional structure is an important material for deep ultraviolet (DUV) optoelectronic devices. However, due to a lack of high-quality and low-cost homogeneous AlN substrates, AlN is mainly prepared by heteroepitaxy on sapphire with a large lattice mismatch. The resulting defect density and residual stress in AlN films become a bottleneck for enhancing the performance of AlGaN-based DUV light-emitting devices. In this paper, the research advances in epitaxial growth and threading dislocation (TD) control of AlN on sapphire substrates at Peking University are described, including decreasing the tilt of AlN grains by nitridation pretreatment of sapphire, forming TD loops by growth mode alternations, bending and terminating TDs at the sidewall of voids by an image force on nano-patterned sapphire substrates, promoting the climbing and meeting of TDs by extrinsic supersaturated vacancies, etc. Based on high-quality AlN with a TD density of ∼108 cm-2, 276 nm DUV light-emitting diodes are fabricated with a light output power of 17.3 mW at an injection current of 100 mA.