Flexible deep-ultraviolet light-emitting diodes for significant improvement of quantum efficiencies by external bending

Deep ultraviolet (DUV) light at the wavelength range of 250‒280 nm (UVC spectrum) is essential for numerous applications such as sterilization, purification, sensing, and communication. III-nitride-based DUV light-emitting diodes (DUV LEDs), like other solid-state lighting sources, offer a great potential to replace the conventional gas-discharged lamps with short lifetimes and toxic-element-bearing nature. However, unlike visible LEDs, the DUV LEDs are still suffering from low quantum efficiencies (QEs) and low optical output powers. In this work, reported is a new route to improve QEs of AlGaN-based DUV LEDs using mechanical flexibility of recently developed bendable thin-film structures. Numerical studies show that electronic band structures of AlGaN heterostructures and resulting optical and electrical characteristics of the devices can be significantly modified by external bending through active control of piezoelectric polarization. Internal quantum efficiency (IQE) is enhanced higher than three times, when the DUV LEDs are moderately bent to induce in-plane compressive strain in the heterostructure. Furthermore, efficiency droop at high injection currents is mitigated and turn-on voltage of diodes decreases with the same bending condition. The concept of bendable DUV LEDs with a controlled external strain can provide a new path for high-output-power and high-efficiency devices.