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6 July 2004365-nm ultraviolet-light-emitting diodes with an output power of over 400 mW
We fabricated high power ultraviolet (UV) light emitting diodes (LEDs), whose emission wavelength is around 365 nm. We found that, in order to improve the external quantum efficiency (ηex) of UV LEDs, it is very important to reduce the optical self-absorption and the threading dislocation density (TDD) of epi-layers. Therefore, at first, UV LEDs epi-layers were grown on high-quality GaN templates (TDD = 2x 108/cm2) with sapphire substrates, and then the GaN templates and the sapphire substrates were removed by using laser-induced lift-off and polishing techniques. As a result, we obtained the low self-absorption and low TDD UV LEDs. When this UV LED was operated at a forward-bias pulsed current of 500 mA at room temperature (RT), the peak wavelength, the output power (Po), the forward voltage (Vf) and the ηex were 365 nm, 410 mW, 5.3 V, 24%, respectively. Moreover, at a forward-bias direct current of 500 mA at RT, Po, Vf and ηex were 360 mW, 5.0 V, 21%, respectively.