High Internal Quantum Efficiency Deep UV Emission from Spontaneously Forming Lateral Heterostructures in High‐Al Content AlGaN Alloys Grown by High‐Temperature Plasma‐Assisted Molecular Beam Epitaxy

We demonstrate that high‐Al content ( x > 0.6) Al x Ga 1− x N films grown in the III‐rich regime by plasma‐assisted molecular beam epitaxy at elevated growth temperatures, ≥900 °C, possess strong, red shifted room temperature (RT) photoluminescence (PL) correlated with the presence of lateral nanoscale periodic oscillations in Al composition. As the growth temperature increased from 800 to 900 °C, additional peaks in the PL spectrum appear at ≈275–280 nm and ≈250–255 nm, strongly red shifted from the fundamental absorption edge at ≈240 nm. This PL is characterized by a total internal quantum efficiency (IQE) as high as 58%, while wavelength selective pumping of the ≈275 nm peak exhibits an IQE of 63%, obtained by comparison of low and RT PL. Scanning transmission electron microscopy shows an oscillating compositional variation of ±5% Al content in the growth plane with a periodicity of ≈11 nm. This behavior is suppressed in films grown at 800 °C, which only exhibit near‐band‐edge PL with an IQE of 4%. Since the lateral composition modulation of the Al x Ga 1‐ x N band structure does not correspond to the red shifted PL peak positions, these results suggest that the PL emanates from localized emitting states at the periodic interfaces of the lateral heterostructure.