Light emitting diode based on n-Zn0.94M0.06O nanorods/p-GaN (M= Cd and Ni) heterojunction under forward and reverse bias

Abstract

In this study, we report on the improvement in the optoelectronic properties of n-ZnO nanorods/p-GaN heterojunction. This was achieved by doping the ZnO with cadmium (Cd) and nickel (Ni). The ZnO and Zn0.94M0.06O nanorods grown hydrothermally on the p-GaN substrate were used to fabricate the light emitting diodes (LEDs). Structural measurement revealed that nanorods with wurtzite structure having a preferential orientation along the (002) c-axis. The UV-vis spectra show that the optical band gap of Zn0.94M0.06O nanorods is decreased in comparison to ZnO nanorods. Electrical measurements of the fabricated LEDs show an obvious rectifying behaviour with low threshold voltage. Electroluminescence (EL) characteristics of LEDs operated at forward and reverse bias were investigated. The EL spectra under forward bias show that doping ZnO nanorods with Cd and Ni led to an intensity enhancement of the broad peak in the visible region while the blue peak originating from the p-GaN substrate remains almost unaffected. The effect of doping was to reduce the valence band offsets and consequently more hole injection has occurred leading to the observed enhancement of the broad band in the visible region. Under reverse bias all heterojunction LEDs show the blue light emission peak originating from the p-GaN substrate.

ZnO-based deep-ultraviolet light-emitting devices

“…In order to bypass the challenging p-type doping of wide bandgap MgZnO, the MgZnO-based heterostructures have been extensively studied by employing p-GaN as the holetransporting layer recently. [15,[33][34][35] In 2009, Zhu et al reported on the fabrication of an n-Mg 0.12 Zn 0.88 O/p-GaN heterojunction LED with an MgO dielectric interlayer by plasmaassisted molecular beam epitaxy technique. [34] By the proper engineering of the band alignment of the heterojunction with using the MgO layer, most electrons are confined in the Mg 0.12 Zn 0.88 O layer under positive bias, while holes can be injected into the Mg 0.12 Zn 0.88 O active layer from the p-GaN side, and the typical EL spectra from the heterostructure are shown in Fig.…”

High photocurrent gain in NiO thin film/M-doped ZnO nanorods (M=Ag, Cd and Ni) heterojunction based ultraviolet photodiodes

“…Also, two broad deep level emission (DLE) peaks were observed for the ZnO nanorods and were extended approximately from 1.80 eV to 2.08 eV (DLE1, red emission) and from 2.09 eV to 2.86 eV (DLE2, green emission). The green and red emissions are ascribed to the recombination of electron-hole pairs between the conduction band or zinc interstitial (Zni) energy level to oxygen vacancy (VO) and oxygen interstitial (Oi) energy level, respectively [28,29]. To investigate the optical quality of the pure and doped ZnO nanorods, the intensity ratio INBE/IDLE was measured, and is demonstrated in Figure 3(b), where INBE and IDLE are the integrated intensity of the NBE and the DLE peaks, respectively.…”