KEYWORDS: Indium gallium nitride, Solar cells, Laser irradiation, Resistance, Temperature metrology, Laser applications, Wireless energy transfer, Sapphire, Retina, Power supplies
We tested the optical wireless power transmission (OWPT) using InGaN photovoltaic cells and lasers below 400 nm. As a result, 24.5% and 20.8% photoelectric conversion efficiencies were obtained at laser power densities of 16.5 mW/cm2 and 398 mW/cm2, respectively. The conversion efficiency decreased as incident laser power increased. On the other hand, the conversion efficiencies increased with increasing the temperature of the InGaN photovoltaic cells. We investigated the causes of these phenomena and found that lower resistance and improved crystal quality of InGaN cells significantly improve conversion efficiency further.
In recent years, reports on highly efficient UV LEDs and UV laser diodes have been published one after another. Considering the application field of UV semiconductor light-emitting devices, it is essential to achieve high output, i.e., high current density operation, and it is important to establish a fabrication process for vertical devices to realize this. A 1cm square wafer with deep-UV LEDs stacked on a sapphire substrate was successfully separated from the substrate to fabricate vertical LEDs. In this study, an Al0.68Ga0.32N underling layer was formed on an AlN template with periodic pillars, and a process that enables reproducible substrate detachment was successfully developed. The fabricated vertical LEDs successfully exhibit remarkable luminescence characteristics (peak wavelength: 298 nm) up to a current density of ~43 kA cm-2 at room temperature and pulse driving. Applications to high-power ultraviolet region LEDs and laser diodes are expected.
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