Baijun Zhao

Control of conductivity type in undoped ZnO thin films grown by metalorganic vapor phase epitaxy

The properties of the ZnO thin films prepared by metalorganic vapor phase epitaxy under various oxygen partial pressures were thoroughly studied. It was found that the conduction type in undoped ZnO epilayers could be controlled by adjusting the family VI precursor, oxygen partial pressure during growth. The films were characteristic of n-type conductivity under oxygen partial pressure lower than 45 Pa. With the increase of oxygen content, the crystallinity of the ZnO thin films was degraded to polycrystalline with additional (10–12) orientation and the intrinsic p-type ZnO was produced as the oxygen partial pressure was larger than 55 Pa. The hole concentration and mobility could reach to 1.59×1016 cm−3 and 9.23 cm2 V−1 s−1, and the resistivity was 42.7 Ω cm. The near-band-edge emission and the deep level emission in photoluminescence (PL) spectra at room temperature were influenced strongly by the oxygen partial pressure. Temperature-dependent PL spectra in n-type ZnO films showed a dominant neutral-don...

Effect of annealing on ZnO thin films grown on (001) silicon substrate by low-pressure metalorganic chemical vapour deposition

ZnO thin films were deposited on (001) Si substrate by low-pressure metalorganic chemical vapour deposition. Thermal annealing was performed at 800 °C in air for an hour. The effects of annealing on the surface morphology, stoichiometric ratio, structural and optical properties of ZnO films were investigated using scanning electron microscopy, x-ray photoemission spectroscopy (XPS), x-ray diffraction, Raman spectra and photoluminescence spectra. The resistivity of ZnO film increased to 1.25 × 102 Ω cm after annealing. It was found that the quality of ZnO film could be improved through annealing.

Effect of the oxygen partial pressure on the properties of ZnO thin films grown by metalorganic vapor phase epitaxy

ZnO thin films were grown on c-plane sapphire substrate at 600°C by metalorganic vapor phase epitaxy (MOVPE). The effect of one of the main deposition parameters, the oxygen partial pressure, on the properties of the ZnO thin films was investigated by means of X-ray diffraction (XRD), photoluminescence (PL) spectrum, atomic force microscopy (AFM) and Hall measurements. Increasing the oxygen partial pressure up to 65 Pa was found to degrade the crystallinity of the ZnO thin films because of the formation of the oxygen-induced defects, but the UV emission in PL spectra was enhanced and deep level emission was weakened. It might be attributed to the reduction of the oxygen vacancies concentration. So the UV emission might be more dependent on the stoichiometry than the microstructural quality of the ZnO thin films. At the same time, Hall measurements showed that the electrical resistivity of the ZnO thin films increased with the oxygen pressure and the electron mobility decreased. The origin of n-type character in undoped ZnO films was the oxygen vacancies.

Preparation and optimization of ZnO films on single-crystal diamond substrate by metal-organic chemical vapour deposition

High-quality ZnO thin films have been grown on single-crystal diamond substrates with (111) orientation, by low-pressure metal-organic chemical vapour deposition. X-ray diffraction spectra and photoluminescence (PL) spectra clearly showed that the quality of ZnO films was improved by the two-step growth method. Strong ultraviolet emissions and weak deep-level emissions with different intensity were both observed in the room-temperature PL spectrum. The change of surface morphology was also studied by atomic force microscopy. Zn and O elements in the deposited ZnO/diamond films were investigated by x-ray photoelectron spectroscopy, in which the statistical result of the ratio for O/Zn atoms of samples was about 1. Raman scattering was performed at room temperature. The E2, A1(TO) and E1(TO) mode peaks were seen at 437.46, 383 and 414.87 cm−1, which indicated a high crystalline quality for our samples.

ZnO thin films growth, characteristics and applications

Undoped, n-doped and p-type ZnO as well as MgZnO alloy thin films were grown by metal-organic chemical vapor deposition (MOCVD) on sapphire. The structural, optical and electrical properties of ZnO films were investigated using X-ray diffraction (XRD), Raman spectrum, photoluminescence (PL) spectrum, transmission spectra and Hall effect, respectively. ZnO ultraviolet (UV) detectors and acoustic surface wave filter (ASWF) devices were fabricated. Additionally, a new ZnO transistor structure was proposed.

ZnO thin films grown by plasma-assisted metal-organic vapor phase epitaxy

ZnO films were grown by metal-organic chemical vapor deposition (MOCVD) on sapphire and Si substrate. Thermal annealing was performed on ZnO thin films deposited on Si substrate. X-ray diffraction spectra indicated that all ZnO films were strongly c-oriented. Strong ultraviolet (UV) emission was observed. X-ray photoelectron spectroscopy (XPS) measurements were performed to confirm the stoichiometry of ZnO film. Optical pumped UV lasing was obtained at room temperature. N-doped ZnO samples were realized by ionizing N/sub 2/ and NH/sub 3/. High resistive ZnO films were obtained by N-doping.