Synthesis And Investigation Of ZnO Nanostructure And Device

Zinc oxide(ZnO) is a unique semiconductor material with a wide direct band gap of 3.37 eV and a relatively large exciton binding energy of 60 meV at room temperature.In recent year,it has attracted increasing interests.It has been regarded as one of the most promising candidates for the next generation of short-wavelength light emitting diode(LED) and laser devices.With the development of nanoscience and nanotechnology,semiconductor nanomaterials will have great influences not only in the fields of physics,chemistry,biology and material science,but also in medicine and information technology.The availability of a rich genre of nanostructures makes ZnO an ideal material for nanoscale optoelectronics devices in the visible and near ultraviolet regions.Furthermore,functional devices such as nanostructure field-effect transistors(FETs),electromechanical coupled sensor,piezoelectric nanosensors,surface acoustic wave(SAW) device,micro-electro mechanical systems (MEMS) and nanolasers have already been realized.Moreover,since ZnO is a biocompatible material,ZnO nanomaterials are expected to be used for biochemical,biomedical,and biomolecular applications.In addition,various techniques are employed to fabricate ZnO nanostructures,such as chemical vapor deposition(CVD),metal-organic chemical vapor deposition(MOCVD),thermal evaporation,molecule beam epitaxy(MBE),etc.Therefore, ZnO nanostructures have attracted so much attention,and a large number of publications have been presented recently for reporting ZnO nanostrucmres with diverse morphologies and properties grown by different approaches.In order to develop nano-scale devices based on ZnO,fabrication high quality ZnO nanostructure arrays and p-type ZnO nanostructures are essential.The assistance of metal catalysts is the most widely used technique for synthesis aligned ZnO nanostrucmres.However.metal catalysts commonly introduce extra impurities defects in the products.Consequently.it is necessary to develop catalyst-free growth techniques of ZnO nanostructures.As we known,there is no report about catalyst-free preparing ZnO nanostructures by pulse laser deposition(PLD) technique.In this thesis,ZnO nanonod arrays were deposited on InP(001) wafer by PLD system with a KrF excimer laser.ZnO seed-layer and buffer-layer rather than metal was used as the catalyst for fabricating ZnO nanostructure. The synthesized ZnO nanorod arrays exhibited a strong c-axis preferential growth orientation with high crystalline quality,and well optical quality.It reveals that the method is a effective technique for growing ZnO nanostructures without metal catalysts.The well aligned and separated ZnO nanorods fabricated by this comparatively simple technique sheds light on further applications for nano-devices.ZnO is naturally an n-type materials,p-type doping is still a bottleneck to device fabrication.Both theoretical model and experimental results illustrate that phosphorus element may act as effective p-type dopants for ZnO thin films.As for the development of ZnO:P nanostructures,very few reports have been published thus far.In this thesis,ZnO:P nanorods and nanoneedles were successfully synthesized by phosphorus diffusion from an InP substrate using a PLD technique.Low temperature(10 K) PL spectra near-band-edge emission peaks were attributed to acceptor-related A⁰X,FA,and DAP transitions.The effect of p-doping on the optical characteristics of the ZnO nanorods was investigated by excitation intensity and temperature dependent PL spectra.Morover,the value of the acceptor energy level of the phosphorus dopant,determined by experimental data and fitting,agree well with the corresponding theoretical and experimental values in ZnO:P films and nanowires.Although p-type ZnO thin films have been reported by some research groups,the availability of p-type doping ZnO nanostructure is very scarce.The Lack of p-type ZnO nanostructure is currently the major factor precluding the realization of a wide range of functional nanodevices based on ZnO.High-quality novel undoped and phosphorus-doped ZnO nanotetrapods were synthesized on sapphire substrates by a simple chemical vapor deposition(CVD) method.Phosphorus doping was performed by using P₂O₅ as the dopant source.Low temperature PL spectrum exhibited acceptor related emission peaks.P-type doping signals were confirmed by temperature and excitation intensity dependent PL measurements.X-ray diffraction and selected area electron diffraction results revealed that crystalline quality and structure of ZnO single crystals were not degraded by phosphorus doping.The binding energy of phosphorus acceptor dopant was established to be about 120 meV.The synthesis of p-type doping ZnO nanotetrapods sheds light on further applications for nanolasers,nanosensors,biocompatible materials etc..and opens up enormous opportunities for nanoscale electronics,optoelectronics and biologics.The simple ZnO nanowire-based field effect transistor(FET) was fabricated by linking up a ZnO nanowire with two Au electrodes,where ZnO nanowires were synthesized by chemical physics deposition,Au electrodes were fabricated using photolithography and electron beam evaporation technologies.The current-voltage results presented favorableâ… -â…¤characteristics curves.