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Conventional ultraviolet (UV) lamps for disinfection emit radiation in the255-270 nm range, which poses a high risk of causing cancer and cataracts. Toaddress these concerns, solid-state far UV-C sources emitting below 240 nm aregaining attention as a safe and sustainable disinfection solution for occupiedspaces. Here, we delve into the extension of the AlxGa1-xN/AlN quantum dot (QD)technology towards the far UV-C range, which presents various challengesassociated with the reduction of the lattice mismatch and band offset when Alis incorporated in the QDs. We explore the structural and optical impact ofincreasing the Al content through the increase of the Al flux and eventualcorrection of the Ga flux to maintain a constant metal/N ratio. We also examinethe impact of extreme miniaturization of the QDs, achieved through a reductionof their growth time, on the spectral behavior and internal quantum efficiency(IQE). The high Al content results in QDs with a reduced aspect ratio(height/diameter) and thicker wetting layer when compared to the GaN/AlNsystem. Self-assembled QDs grown with a metal/N ratio ranging from 0.5 to 0.8show an IQE around 50%, independent of the Al content (up to 65%) or emissionwavelength (300-230 nm). However, samples emitting at wavelengths below 270 nmexhibit a bimodal luminescence associated with inhomogeneous in-plane emissionattributed to fluctuations of the QD shape associated with extended defects.Reducing the QD size exacerbates the bimodality without reducing the emissionwavelength. The power efficiencies under electron beam pumping range from 0.4%to 1%, with clear potential for improvement through surface treatments thatenhance light extraction efficiency.

cornell university

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