Enhanced optical output power of InGaN/GaN vertical light-emitting diodes by ZnO nanorods on plasma-treated N-face GaN

Light-emitting diodes (LEDs) play an important role as a formidable contender for next-generation lighting sources and rapidly replace conventional lighting sources. In this report, the growth of high density inclined ZnO nanorods (NRs) on the N-face n-GaN surface for high efficiency vertical light-emitting diodes (VLEDs) is demonstrated based on oxygen plasma pretreatment and hydrothermal growth. Surface modification by oxygen plasma pretreatment efficiently produces GaOx nanoparticles on the N-face n-GaN surface and they play an important role in the hydrothermal growth of dense and inclined ZnO NRs. The optical output power of ZnO NR VLEDs following oxygen plasma pretreatment is strongly enhanced by a factor of 3.25 at an injection current of 350 mA, compared to that of planar VLEDs. The large enhancement of optical power is attributed to the dense ZnO NR layer which efficiently reduces the total internal reflection and enhances the waveguide effect in ZnO NRs.