The Growth Of ZnO Films By Metel-organic Chemical Vapor Deposition (MOCVD) And The Fabrication And Study Of ZnO UV Detector

ZnO, a wide direct-gap semiconductor, attracts as much attention as GaN in optoelectronics research field. Its optoelectronic characteristics are little affected by vacancies. And it has great uses in this information age. It can be used to fabricate display devices, high frequency filters, emitting diode, lasers, high speed optical switch and so forth. Therefore, it has great uses in both civil and military fields.At present, the research of ZnO is mainly about the growth of material films. A lot of methods have been used to deposit ZnO films such as Molecule Beam Epitaxy (MBE), Metal-organic Chemical Vapor Deposition (MOCVD), Pulsed Laser Deposition (PLD), Atomic Layer Epitaxy (ALE), Sputter and Thermal Evaporation. In this thesis, we grew high quality ZnO films by plasma-assisted MOCVD system on c-Al2O3 substrate and studied their related characteristics. Meanwhile, based on high resistance ZnO films grown by MOCVD, we successfully designed and fabricated ZnO ultraviolet photodetector. Then characterization and analysis were performed.We grew high quality ZnO films by MOCVD on c-Al2O3 substrate and investigated the characteristics of them. X-ray Diffraction (XRD) shows that ZnO films are highly c-oriented and the full width at half maximum (FWHM) of (0 0 2) ZnO is 0.28(. Related analysis indicated that a tensile strain was formed in the deposition process of ZnO. In room temperature Photoluminescence (PL) Spectra, we observed high-intensity ultraviolet luminescence. The ratio of ultraviolet luminescence intensity and green luminescence intensity is 14:1 and the forbidden band width derived from PL spectrum is about 3.31 eV, which indicated good optical quality of ZnO films.We compared ZnO films grown on c-Al2O3 in different conditions. Firstly, we optimized the growth temperature. Results and analyses show that ZnO thin film grown with the temperature of 5400C has the best crystal quality and optical quality.We systemically studied the effect of the temperature of DEZn source on the quality of ZnO films grown by MOCVD. XRD spectra show that the change of DEZn source temperature little effects lattice constant of ZnO, which also means that the temperature change of DEZn source has little influence on the built-in tensile strain in ZnO. ZnO film grown with the temperature of －19(C had the best crystal quality. Atomic Force Microscopy measurements show that ZnO grown at －19(C had the smallest roughness. PL spectra show that the ultraviolet luminescence energy of samples decreased with the decrease of DEZn source temperature and increased after －21(C. Considering in lattice-mismatched epitaxial growth, ZnO thin film has a tensile built-in strain, so this shift of band gap energy is related to the structure characteristic of ZnO films (tensile built-in strain in films). Therefore, the decrease of ultraviolet luminescence energy means that the decrease of tensile strain in ZnO. Results show that tensile built-in strain of ZnO is the smallest when DEZn temperature is about －19(C～－21(C and has little fluctuation. This indicates that in some range the change of DEZn temperature has little effect on tensile strain in ZnO films. This result is in accordance with the analysis of XRD. Sample grown at －19(C has the highest ratio of ultraviolet luminescence intensity and green luminescence intensity, which shows the best optical quality. Synthetically, ZnO films grown with the temperature of －19(C has the best quality. Post-thermal annealing, as one common means to improve films' quality, at high temperature can make ZnO bonds undergo a relaxation process to cause network reconstruction. So we investigated the influence of post-thermal annealing on ZnO films. Thermal annealing was performed on ZnO films in vacuum, air and O2. The experimental results showed that the resistivity of ZnO decreased slightly after thermal annealing in vacuum while it increased strongly after thermal annealing in air and O2. The intensity of green emission increased sharply after annealing in air and O2 while it almost di...