Suppression of dislocation-induced spiral hillocks in MOVPE-grown AIGaN on face-to-face annealed sputter-deposited AIN template

摘要

AlGaN films were grown on face-to-face annealed sputter-deposited AIN/sapphire (FFA Sp-AIN) templates via metalorganic vapor phase epitaxy (MOVPE), and the growth behavior of the AIGaN films was investigated. The sapphire substrates with small off-cut exhibited poor surface flatness of AIGaN grown on the FFA Sp-AIN templates owing to the formation of large hillock structures. To understand the origin of these hillock structures, the crystallinity and surface morphology of conventional fully MOVPE-grown AIN/sapphire (MOVPE-A1N) templates and the FFA Sp-AIN template were comprehensively studied. The screw- and mixed-type threading dislocation density of the FFA Sp-AIN template was estimated to be approximately 1.8 × 10~6cm~(-2), which was two orders of magnitude lower than that of the MOVPE-AIN template. Consequently, the uniquely observed growth of the hillock structures in the FFA Sp-AIN templates was attributed to their low density of screw- and mixed-type threading dislocations. The large surface off-cut sapphire substrates suppressed the hillock structures on the FFA Sp-AIN templates. The improvement in surface flatness resulted in better optical properties of multiple quantum wells grown on the AIGaN layer. These results demonstrate a promising method for achieving highly efficient and cost effective AIGaN based deep ultraviolet light-emitting diodes.