GaN/ZnO nanorod light emitting diodes with different emission spectra

Abstract

Light emitting diodes (LEDs) consisting of p-GaN epitaxial films and n-ZnO nanorods have been fabricated and characterized. The rectifying behavior and emission spectra were strongly dependent on the electronic properties of both GaN film and ZnO nanorods. Light emission under both forward and reverse bias was obtained in all cases, and emission spectra could be changed by annealing the ZnO nanorods. The emission spectra could be further tuned by using a GaN LED epiwafer as a substrate. Both forward and backward diode behavior has been observed and the emission spectra were significantly affected by both the properties of the GaN substrate and the annealing conditions for the ZnO nanorods.

ZnO nanorod/GaN light-emitting diodes: The origin of yellow and violet emission bands under reverse and forward bias

“…6 Under reverse bias, large current has been observed. n-ZnO/p-GaN heterojunction devices without intrinsic or insulating layers frequently show leaky I-V curves 6,9,10,14,17,29 in agreement with large currents under reverse bias observed in our work. Large leakage current was previously attributed to Pool-Frenkel effect.…”

“…2, are consistent with the presence of tunneling mechanisms and show a shape resembling the backward diode. 10,12,13,41 Similar I-V curve shapes can also be observed for QW1 and QW2 devices. 37 The contacts have been verified to be ohmic, 37 as illustrated in the inset of Fig.…”

“…The tunneling is expected to occur due to the large energy band offset at p-GaN/n-ZnO interface. 4,8,10,12,13,28,[45][46][47] The yellow (or orange yellow) emission appears at relatively low bias voltages, so that it likely occurs due to tunneling. Tunneling phenomena in III-nitride heterojunctions have been previously observed for different material combinations.…”

“…23 However, very different behavior has been reported for pGaN/n-ZnO devices even for similar device architectures, which makes it difficult to establish strategies for the improvement of device performance. For example, in addition to devices lighting up under forward bias, devices lighting up under reverse bias 4, [8][9][10]12,13,28 have been reported. Also, a variety of the emission peaks at different wavelengths have been observed, including UV, UV-violet, violet-blue, green, yellow, and orange-red, with multiple peaks frequently present 11,14,18,19,22 which in some cases results in white emission.…”

“…Obtained results indicate that all the emission peaks (orange, yellow, blue under reverse bias, and violet under forward bias), originate from the p-GaN layer and/or GaN/ZnO interface since they can be observed in the absence of ZnO, as discussed in the Subsection III D. To improve the brightness of the devices, we have utilized a simple approach of growing ZnO nanostructures on a commercial group-III nitride-based LED wafer. 10,30 It has been shown that device architectures containing ZnO and InGaN multiple quantum wells (MQWs), [31][32][33] where dominant light emission peak originates from InGaN MQW, [31][32][33] can result in bright devices with low turn-on voltage (2.5 V). 31,32 Thus, we have employed a simple method of growing ZnO nanorods by electrodeposition on top of a commercial, unetched GaN-based LED wafer followed by the deposition of electrode onto ZnO, without any etching steps involved.…”