Study On The Synthesis And Electrical, Optical And Magnetic Properties Of Zinc Oxide Materials

As a wide band gap oxide semiconductor, ZnO has increasingly shown its important research value and potential applications. ZnO has currently become a new hotspot afterwards GaN in the short wavelength semiconductor laser materials and devices area. ZnO optoelectronic materials and devices research and development are bound to affect the level of national economic development and national security, many developed countries have elected ZnO materials and devices to the national strategy of increasing the height, have invested huge amounts of money to carry out related research. Over the last decade, international research has formed a wave of ZnO. At present, the international community in the ZnO-based optoelectronic materials and device research in the field become increasingly competitive. In particular, both in ZnO materials physics, device physics and device technology, there are a lot of basic question has not been well addressed. Practical use of ZnO light-emitting device has not yet made a breakthrough. The current bottleneck restricting the development of the main ZnO is yet to obtain high crystalline quality, low resistance, under controlled and stable performance of the main concentration of p-ZnO thin films. How to prepare a stable and efficient p-type ZnO has become the focus of international research, is currently the primary problem solved. Meanwhile, with some of the unique properties of nanomaterials discovery, ZnO low-dimensional structures are also expected to have single crystal film and the body does not have the physical and chemical properties. In addition, explore the ZnO for spin-based diluted magnetic semiconductor materials, magnetic origins, how to increase the saturation magnetization and Curie temperature still need to improve the lot of exploration and research.In this thesis, I carried out systematicaly investigations on ZnO system, involving thin films and nanowires. Mainly concentrate on studies of the influence of intrinsic defects evolution of ZnO on its conduction, optical and magnetic properties.In detail, there are three aspects as following:1. An undoped ZnO thin film with high resistivity was prepared by rf magnetron sputtering on the quartz substrates using a ZnO (99.999% pure) as target and high pure Ar as sputtering gas. Upon annealing under 10?3 Pa with different temperature, the conductive properties of the film change from n-type to p-type and finally to n-type with increasing annealing temperature. XPS and PL measurements indicate that the undoped ZnO is Zn-rich and has Vo and interstitial Zni donor defects. The amount of Vo and Zni donors changes with the annealing temperature. The intrinsic p-type conduction of the undoped ZnO film is ascribed to that the VZn acceptor concentration can compensate Vo and Zni donors concentration and associated H difussion. The investigations on the origin of p-type conduction of the undoped ZnO films give rise to a certain help to further understand the conductive mechanism of doped ZnO community.2. We studied the structural characteristics and optical properties of well-aligned ZnO nanowire arrays synthesized by vapor transport method. HRTEM results suggest all nanowires possess high crystallinity along [001] growth direction with no structural defect and no cluster formation. Selected area electron diffraction (SAED) patterns indicate no sign of secondary phase, indicating a pure hexagonal ZnO structure. HRXRD angular scan from 30⁴0 degree shows strong and sharp peaks are observed for ZnO (002) and Al₂O₃ (110). No impurity or secondary phase was detected. The dominant (002) ZnO peak indicates the preferred growth orientation of the NWs, and is consistent with the in-plane pole figure with confined (002) reflection. (100) pole figure clearly depicts the six-fold symmetric geometry of hexagonal ZnO structure.These NWs exhibit UV lasing emission at room temperature with remarkably low optical excitation threshold (～60μJ/cm²) compare with lowested value (～70μJ/cm²) reported so far, which is reduved almost 15%. Furthermore, recombination emissions involving carrier dynamics of pure ZnO nanowires were investigated by temperature-dependent TRPL spectroscopy. The decay dynamics can be fitted to two exponential components for the NBE recombination; both of them are influenced by nonradiative phonon effects. We conclude that the free excitons radiative recombination with relatively long lifetime dominates the recombination process below 115 K. While the bound exciton associated lifetime decreased monotonously. Such pure ZnO nanowires are promising for applications in multifunctional photonic nanodevices.3. We fabricated highly crystalline Zn₃N₂ films by using sputtering. The substrate temperature is found to strongly affect the crystal quality of films. We studied the structural characteristics of Mn,N codoped ZnO thin films synthesized by oxidation of Mn-doped Zn₃N₂.The 3D AFM morphology image shows the compact, smooth and uniform film was ontained on quartz substrate. The surface roughness with root mean square mode is around 5 nm and grain size is around 200 nm. XPS measuring results show that Mn atom replace the Zn with Mn²⁺ (binding energy of 640.2 eV) chamical states in the ZnO matrix and accompanied with few amounts of Mn³⁺ (binding energy of 642.6 eV)components. The percentage of Mn²⁺ was ditermined to be around 80% compared with Mn³⁺. N1s XPS core-level peak indicates that there still exist trace amount of solid state of N molecule in Mn,N codoped ZnO films. After calculation, the chemical furmula for Mn,N codoped ZnO film was ditermined to Zn0.974Mn0.026O0.978N0.022, which is consistent with EDS results. Under optimal conditions, 2.6 at.% Mn-doped ZnO:N films (Zn_0.974Mn_0.026O_0.978N_0.022) were obtained reproducibly. Hall measuring results suggest that the Mn,N codoped ZnO samples behave n-type conduction and their resistivity is much higher than that of Mn-doped ZnO samples. Interestingly, these films behave obvious RTFM which is much larger than that of Mn-doped ZnO (Zn_0.974Mn_0.026O) samples. We attribute such enhanced ferromagnetism to the magnetic interaction between the bound magnetic polarons formed in codoped ZnO films which is influenced strongly by the defects type and concentration.