Study Of The Deposition And Hydrogen Treatment Of Cu-doped ZnO Thin Films And The Related LED

As a kind of II-VI wide-band semiconductor, ZnO possessing the particular properties and function, was thought to be the promising materials to fabricate the ultraviolet (UV) optoelectronic devices by the virtue of its direct wide-band gap (-3.37 eV) and large exciton binding energy (-60 meV). However, the lack of the p-type ZnO posed a big difficulty for the further application of ZnO-based optoelectronics devices. Based on the theories, ZnO:Cu is possible p type conductivity, although light-doped ZnO:Cu samples grown by MOCVD is belonging to high resistivity. All the research work in this thesis was performed including the deposition of ZnO:Cu thin films, the hydrogen treated ZnO:Cu by high pressure H2 and the fabrication of n-ZnO/i-ZnO:Cu/p-GaN heterostructure with the ZnO:Cu as the active layers.Firstly, various of ZnO:Cu samples with increasing amount of Cu, under different condition were grown by MOCVD system and then characterized by many methods. In the low temperature PL spectra, it was found that Cu dopant introduced more than one acceptor energy level in energy gap, including localized dopant impurity and the donor energy levels based on the self-compensation in semiconductors. The presence of the DAP (donor and acceptor pair) in LT-PL gave direct evidence that acceptors were really incorporated into ZnO and could have a shallow level. In our ZnO:Cu samples it was proposed to be Cu1+. And based on the TES (two-electron satellite) energy position, the binding energy was calculated about 55 meV,58 meV and 57 meV for the bound excitons in samples.The samples were treated in H2 ambient at high pressure to get the magnified H role in ZnO:Cu samples to find some new phenomenon. Hall-effect measurement results presented that the high resistivity ZnO:Cu samples turn into n-type conductivity after H incorporation. Based on the IR and low temperature PL results, it was thought that the passivation of the acceptor-like defects by the incorporation H was to improve the n-type conductivity. The annealing results indicated that the hydrogenated ZnO:Cu could not recover high resistivity and it was proposed that some unknown H-related donor-like defects still exist in the film after annealing.Last, n-ZnO/p-GaN and n-ZnO/i-ZnO:Cu/p-GaN light-emitting diodes were fabricated by metal organic chemical vapor deposition on sapphire substrate. The only appearance of the EL emission peak at 385 nm in the PIN structure was identified as the radiative recombination in the high resitivity i-ZnO:Cu layer due to its good optical quality. This study suggested that high-resistivity ZnO:Cu thin films could serve as a good active layer.