Improvements in Structural and Optical Characteristics of N-Polar AlGaN Films Deposited on In Situ Grown GaN Hexagonal Prisms

Abstract

In situ GaN hexagonal prisms were deposited successfully and were employed to realize epitaxial lateral overgrowth (ELOG) of N-polar Al0.34Ga0.66N films for the first time. Specifically, the influences of the coverage of GaN hexagonal prisms on the characteristics of N-polar AlGaN films were explored intensively. According to the measurement results, the surface flatness, threading dislocation densities, and the luminescent characteristics of N-polar AlGaN could be modulated by optimizing the coverage of GaN hexagonal prisms. Compared with the reference sample grown without GaN hexagonal prisms, the surface roughness in the optimal sample grown with a fine-tuned coverage of GaN hexagonal prisms decreased by 86.4%. Meanwhile, reductions of more than 1 order of magnitude in both screw and edge dislocation densities were achieved for the optimal sample. Moreover, the blue-band emission in the optimal sample was also suppressed effectively. The substantial improvements in the characteristics could stem from the GaN hexagonal prism-induced ELOG, resulting in dislocation annihilation and strain relaxation in N-polar AlGaN films.