The Preparation And Photoelectric Properties Of ZnO/GaN Heterojunction Light-emitting Diode

ZnO is a multifunctional semiconductor with a wide band gap of 3.37eV. This material has a high exciton emission efficiency at room temperature because of its large exciton binding energy (60 meV). It has extensive application in the field of light-emitting diode (LEDs), semiconductor laser, and solar cell. This paper was focused on the application of ZnO nanomaterials in light-emitting diodes, and the details are as following:A new method to fabricate top electrode of ZnO/GaN heterojunction was proposed using graphite oxide (GO) which can form a film on the top of nanorod arrays. Firstly,GO solution was spincoated on the top of nanorod arrays,which formed a film subsequently. This film covered the gaps among ZnO nanorods,so it can play a supporting role for depositing top electrode. And then ZnO:Ga film was deposited by PLD. Finally,GO was removed by annealing. Thus ZnO:Ga film contacted with ZnO nanorods directly, which formed the top electrode of this device. Results indecated that this method can overcome the shortcomings of traditional methord.The n-ZnO/p-GaN heterojunction LEDs were successfully prepared by this method. Unlike traditional LEDs which realize electroluminescence (EL) only under forward voltages, this heterojunction realized EL both under forward and reverse voltages. Under forward voltages, the EL spectras were dominated by a visible-light emission peaking 650nm. But the EL spectras under reverse voltages were composed of two parts: ultraviolet (UV) emission peaking 365nm and a blue-light emission at around 430 nm. Compared with photoluminescence spectra, variable-temperature EL spectra and EL spectra under variable injection currents, it is easy to learn that the visible-light emission under forward voltages related with ZnO defects, but the UV and blue-light emissions under reverse voltages were attributed to GaN bandedge-emission and Mg-acceptor-related emission, respectively. Based on this special phenomenon, band structures of n-ZnO and p-GaN were used to explain the EL mechanism.