Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Science

Program

Chemistry

Supervisor

Sham, Tsun-Kong

Abstract

Over the past decades, Zinc Oxide (ZnO) semiconductor and its derivatives have been extensively developed because of its optoelectronic properties, such as piezoelectric and photocatalytic properties. Since ZnO is an intrinsic n-type semiconductor; therefore, how to synthesize high-quality p-type ZnO semiconductors with doping and investigate their optoelectronic properties and local chemical structures are important and necessary. This thesis presents two studies of synthesizing both undoped and phosphorus doped ZnO nano/microstructures by hydrothermal method and chemical vapor deposition (CVD) technique, respectively. The local chemical structure and the optical properties of both undoped and P-doped ZnO nano/microparticles are determined by the X-ray absorption near-edge structures (XANES) and X-ray excited optical luminescence (XEOL) technique, respectively. As a result, the P-doped ZnO lattice and substitute the Zn. The oxidation state of P in P-doped ZnO is 5+. The P-doped ZnO products have better crystallinity and less oxygen-based surface defect than the undoped ZnO products.

Summary for Lay Audience

Zinc Oxide (ZnO) is one of the important II-VI semiconductors and remains a popular research topic in today’s scientific field due to its optoelectronic properties such as piezoelectric, photocatalytic properties. It is a versatile wide bandgap semiconductor that has been used widely for a range of applications including sensors, lasers and photovoltaic devices. With a wide bandgap of 3.4 eV and a large exciton binding energy of 60 meV, ZnO has been recognized as one of the most promising materials in the next generation optoelectronic devices area. In this thesis, two studies of synthesizing both undoped and P- doped ZnO nano/microstructures by hydrothermal method and chemical vapor deposition (CVD) technique are presented. Two laboratory techniques and two synchrotron-based techniques are used for characterization in this thesis. Scanning electron microscopy (SEM) and laboratory X-ray diffraction (XRD) are used to track the surface morphology and the crystalline structure of both undoped and P-doped ZnO nano/microstructures, respectively. X-ray absorption near-edge structures (XANES) and X-ray excited optical luminescence (XEOL) are also used to determine the local chemical information of both undoped and P-doped ZnO nano/microstructures such as local symmetry and optical properties. It is found that, the P is successfully doped into the ZnO lattice and the oxidation state for P in P-doped ZnO samples is 5+. The P-doped ZnO products have better crystallinity and less oxygen-based surface defect than the undoped ZnO products. The bandgap for the undoped ZnO structure prepared by the hydrothermal method and CVD technique are 3.20 and 3.22eV, respectively. The bandgap for P-doped ZnO prepared by CVD technique is 3.21eV.

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