Fabrication of ZnO homojunction-based color-switchable bidirectional LEDs by using a hydrothermal growth method

Abstract

In this study, zinc oxide (ZnO) homojunction-based light-emitting diodes (LEDs), with variable emission wavelengths depending on the bias polarity, have been fabricated using a simple hydrothermal growth method. The p-type doping of ZnO nanorods (NRs) was achieved using Sb in the precursor solution and the homojunction was fabricated by epitaxial growth of Sb-doped p-type ZnO NRs on top of n-type ZnO NRs. The fabricated devices emitted light under forward and reverse bias with a turn-on voltage of 2.7 V and a breakdown voltage of −3.7 V. The emission wavelength of the devices was dependent on the bias polarity, owing to changes in the types of carrier recombinations. Under forward bias, mixed violet, yellow, and red colored emissions were mainly observed, corresponding to the emission peaks at 475, 625 and 700 nm, respectively, whereas only red colored emission was prominent under the reverse bias, corresponding to a single broad peak centered at 730 nm. Under forward bias, the near-band edge emission (NBE) was red-shifted from 378 to 475 nm, which was attributed to a localized surface plasmon resonance (LSPR) effect due to the presence of silver nanoparticles (Ag NPs) formed after annealing of the Ag top electrode. No NBE was observed under reverse bias owing to carrier recombination with existing defects, leading to discordance in the resonance energy with the Ag NPs, and thus no LSPR effect.