Characteristics of hexagonal V pits in AlGaN films grown on patterned GaN templates

We reported an investigation of physical properties of AlGaN films grown on patterned GaN templates. It is found that with the patterned grooved-GaN templates, it is possible to manipulate the formation of the V-shape pits and optical property of AlGaN films. For a trench depth of 1.0 um, the V-shape pits can be greatly suppressed. While the GaN trench depth is up to 1.5 um, a large number of the V-shape pits present along the trench. Cathodoluminescence (CL) spectra show a strong band-edge emission around the V-shape pits. Transmission electron microscopy (TEM) data suggest that the spatial variation of intensity is due to the absence of dislocations in the sidewall of the V-shape pit. Cross-sectional CL spectrum and energy-dispersive X-ray (EDX) show compositional variation in the V-shape pits. The formation of Ga-rich domains exists in the invert apex of the V-shape pits, which induces a large density of non-radiative centers and reduces the emitted intensity. Finally, combining with the scanning Kelvin microscopy measurement, the energy band alignment of the V-shape pits is constructed for the first time, which is very useful for the understanding of physical properties of the V-shape pits.