Abstract
We demonstrate that the morphology effect on the ZnO surface using organic acids significantly improves the photon extraction efficiency of III-nitride emitters. Oxalic (C2H2O4), citric (C6H8O7), and formic (CH2O2) acids were used for modulating the nanostructured surface of the ZnO layer with various shapes, including random nanoblocks, nanoholes, and nanorods. The transmittance of the nanostructured ZnO layer fabricated with formic acid for 3 min was 91% at 450 nm wavelength. The optical output power intensities of the emitters with the nanostructured ZnO surface layer were enhanced by 22.14%, 30.58%, and 22.46% with oxalic, formic, and citric acid, respectively, compared with the emitter with the flat ZnO layer.
Highlights
The photon extraction of III-nitride emitter devices is mainly governed by the probability of the photons generated in the active layer escaping from the higher refractive index of the semiconductor into the lower refractive index of the surrounding material
The epilayers consisted of a p-GaN (0.25 μm), 5-period InGaN/GaN multiple-quantum wells (MQWs), an n-GaN (1.5 μm), and an undoped GaN (u-GaN) layer grown on sapphire substrate (430 μm thickness)
It is shown that the surface morphology modulation in the ZnO layer using three organic etchants maintained the good electrical properties of emitters without significant degradation
Summary
The photon extraction of III-nitride emitter devices is mainly governed by the probability of the photons generated in the active layer escaping from the higher refractive index of the semiconductor into the lower refractive index of the surrounding material (air or resin). To obtain zE-mail: kim.kk@kpu.ac.kr various surface morphologies of the ZnO layers, the etching time was tested from 1 to 5 min for all three etchants.
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