Electro-optical and Cathodoluminescence properties of low temperature grown ZnO nanorods/p-GaN white light emitting diodes

Vertically aligned ZnO nanorods (NRs) with a diameter in the range of 160-200 nm were grown on p-GaN/sapphire substrates by aqueous chemical growth technique and white light emitting I diodes (LEDs) are fabricated. The properties of this LED were investigated by parameter analyzer, cathodoluminescence (CL), electroluminescence (EL), and photoluminescence (PL). The I-V characteristics of the fabricated ZnO/GaN heterojunction revealed rectifying behavior and the LED emits visible EL when bias is applied. From the CL it was confirmed that both the ZnO NRs and the p-GaN are contributing to the observed peaks. The observed EL measurements showed two emission hands centered at 450 nm and a second broad deep level defect related emission centered at 630 nm and extending from 500 rim and up to over 700 rim. Moreover, the room temperature PL spectrum of the ZnO NRs/p-GaN reveals an extra peak at the green color wavelength centered at 550 nm. Comparison of the PL, CL, and EL data suggest that the blue and near red emissions in the EL spectra are originating from Mg acceptor levels in the p-GaN and from the deep levels defects present in the ZnO NRs, respectively. The mixture of high and low energy colors, i.e., blue, green, and red, has led to the white observed luminescence. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim