High-efficiency electron-beam-pumped sub-240-nm ultraviolet emitters based on ultra-thin GaN/AlN multiple quantum wells grown by plasma-assisted molecular-beam epitaxy on c-Al2O3

We report the internal structures and emission properties of GaN/AlN single- and multiple-quantum-well (QW) heterostructures with well widths of d w = 1–4 monolayers (MLs), grown by plasma-assisted molecular-beam epitaxy on c-sapphire at metal-rich conditions and low temperatures (~700 °C). The formation of plane QWs with abrupt symmetrical interfaces is confirmed by both scanning transmission electron microscopy and X-ray diffraction analysis. Pulse-scanning and continuous-wave output powers of 150 and 28 mW, respectively, at a peak emission wavelength of 235 nm were achieved at 300 K in an electron-beam-pumped deep-ultraviolet (1.5 ML-GaN/5.5 nm-AlN)360 multiple-QW emitter with a maximum efficiency of 0.75%.