Growth Of ZnO Light-Emitting Devices And Thin Film Transistors By MOCVD

As an II-VI group semiconductor, ZnO has attracted great interest for its wide band gap (3.37eV) and relatively large exciton binding energy (60meV) at room temperature. It has been regarded as one of the most promising candidates for the next generation of ultraviolet (UV) light-emitting diode (LED) and lasing diode (LD) operating at high temperatures and in hard environments.However, after years of research, the progress of ZnO-based light-emitting devices is very slow. One key problem is the lack of device-quality ZnO films, especially the stable and reproducible p-type ZnO films.In this thesis, many research works are conducted to fabricae high quality native ZnO films, p-ZnO films, ZnO-based homojunction and heterofunction short wavelength light-emitting devices. ZnO films and p-type doping of ZnO thin films are grown on many kinds of substrates by Metal-Organic Chemical Vapor Deposition (MOCVD) technique, and the effects of growth conditions on the structural, surface morphology and optical properties of the deposited ZnO films have been investigated.ZnO films are grown by MOCVD on c-plane sapphire and GaN/Al2O3 substrates. The effects of the growth temperature and source gas flow ratios on the properties of the films are analysed and the range of optimized growth conditions are obtained.MIS structure of light-emitting devices is fabricated on ITO-glass substrate by MOCVD, and the material of insulating layer is MgO. The turn-on voltage is about 2V and the reverse breakdown voltage higher than -6 V. Ultraviolet (Center wavelength 379nm) electroluminescence (EL) from ZnO layer are observed under forward bias at room temperature (RT).The p-type ZnO:As layer is formed using GaAs interlayer as the As precursor. The GaAs interlayer was pre-deposited on ITO substrate by sputtering method. The thickness of GaAs interlayer is the key to fabricate the p-ZnO films. When the thickness of GaAs interlayer is 20nm, the electrical properties of As-doped p-ZnO films show hole concentration of 1017/cm3. Based on the p-ZnO:As film, ZnO homojunction LED with is fabricated on ITO-glass by MOCVD. The device exhibits desirable rectifying behaviour. Ultraviolet and visible light electroluminescence are observed from ZnO homojunction device under forward bias at room temperature.P-doped ZnO films (p-ZnO:P) are grown by MOCVD techniques, and sublimate the red phosphorus as the doping source.On this basis, p-ZnO:P/n-GaN heterojunction light-emitting device is fabricated on n-GaN substrate by MOCVD.The device exhibits desirable rectifying behaviour. The electrical pump UV lasing (Centred at 375nm)is detected from this device at room temperature, and the threshold current density is only 1.2A/cm2.ZnO transparent thin-film transistors with MgO as a gate dielectric were fabricated on ITO substrate by all MOCVD technology. The drain current can be modulated by the voltage of gate. Experiment results show that the ZnO-TFTs operate in n-channel mode with an on/off ratio about 105.