Cu And Ga Doped ZnO Thin Films And Related Light Emitting Diodes

The main objective of this dissertation is to study the key aspects of ZnO thin films fabricated by metal-organic chemical vapor deposition (MOCVD) for optoelectronic devices. ZnO has received attention due to its direct band gap of3.37eV at room-temperature, large exciton bonding energy of60meV, alloying and doping capabilities. In this study, ZnO thin films were grown on c-plane sapphire and Si (111) substrates by MOCVD and then, these films were mainly studied in terms of their structural, morphology, op tical and e lectrical properties. The studied key aspects include Ga-doping, Cu-doping and Cu-Ga codoping of ZnO thin films, the suggestion of micro physical mechanisms of impurity doping, fabrication of homojunction, and fabrication of heterojunction using SiO2and Ga2O3as carrier blocking layers.N-type ZnO:Ga thin films have been studied. It is suggested that Ga incorporation decreases the Fermi level and the formation energy of native acceptor defects.Cu-doped ZnO thin films grown on Si (111) substrates were studied. A characteristic green-luminescence with fine structure consisted of doublets emission peak was observed from low-temperature photo luminescence (11.4K), which was believed to be associated with Cu doping. A theoretical model based on hydrogen analogue has been proposed to explain this phenomenonP-type conductivity in ZnO thin films was obtained from Cu and Ga codoping. The Cu-Ga codoped ZnO thin film shows p-type conductivity with resistivity of0.2499ΩQ-cm, mobility of13.3cm2V-1s-1, and carrier concentration1.874×1018. Homojunction with Cu-Ga codoped ZnO/ZnO single crystal structure was fabricated. Near band edge electroluminescence (EL) was observed from the junction under forward-bias current under roo m temperature.UV-emitting n-ZnO/SiO2/p-GaN devices were fabricated. EL spectra of the devices were measured frombothn-ZnO side and p-GaN side. The role of SiO2was rediscovered.N-ZnO/Ga2O3/p-GaN heterojunction light-emitting diodes were fabricated. Compared with the n-ZnO/p-GaN structure, the deep level visible emission at525nm was completely suppressed while UV emission at-392nm was significantly improved in ZnO/Ga2O3/p-GaN structure. The role of Ga2O3in n-ZnO/p-GaN heterojunction LED was discussed indetail.