AlGaN/AlN Stranski–Krastanov Quantum Dots for Highly Efficient Electron Beam-Pumped Emitters: The Role of Miniaturization and Composition to Attain Far UV-C Emission

Conventional ultraviolet (UV) lamps for disinfection emit radiation in the\n255-270 nm range, which poses a high risk of causing cancer and cataracts. To\naddress these concerns, solid-state far UV-C sources emitting below 240 nm are\ngaining attention as a safe and sustainable disinfection solution for occupied\nspaces. Here, we delve into the extension of the AlxGa1-xN/AlN quantum dot (QD)\ntechnology towards the far UV-C range, which presents various challenges\nassociated with the reduction of the lattice mismatch and band offset when Al\nis incorporated in the QDs. We explore the structural and optical impact of\nincreasing the Al content through the increase of the Al flux and eventual\ncorrection of the Ga flux to maintain a constant metal/N ratio. We also examine\nthe impact of extreme miniaturization of the QDs, achieved through a reduction\nof their growth time, on the spectral behavior and internal quantum efficiency\n(IQE). The high Al content results in QDs with a reduced aspect ratio\n(height/diameter) and thicker wetting layer when compared to the GaN/AlN\nsystem. Self-assembled QDs grown with a metal/N ratio ranging from 0.5 to 0.8\nshow an IQE around 50%, independent of the Al content (up to 65%) or emission\nwavelength (300-230 nm). However, samples emitting at wavelengths below 270 nm\nexhibit a bimodal luminescence associated with inhomogeneous in-plane emission\nattributed to fluctuations of the QD shape associated with extended defects.\nReducing the QD size exacerbates the bimodality without reducing the emission\nwavelength. The power efficiencies under electron beam pumping range from 0.4%\nto 1%, with clear potential for improvement through surface treatments that\nenhance light extraction efficiency.\n