A light-emitting diode (LED) consisting of an ultraviolet (UV) InGaN/AlGaN multiple quantum-well (MQW) p-i-n structure and a ten-pair green unipolar InGaN/GaN MQW grown on the same sapphire substrate was investigated. After a series of device-processing procedures, including wafer bonding and laser liftoff, the proposed UV LED structure, which features a visible indicator formed through selective-area photon recycling and exhibiting a dual-peak spectrum comprising UV and green peaks, was produced. The green peak originated from UV light generated by the electrical pumping of the epitaxially stacked green MQW. The green light emission may practically be used in indicators and warning signs during the operation of UV LEDs. The current-dependent light output of the green peak may further serve as a reference for measuring the output power of the UV peak of the proposed UV LEDs.
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