Study Of The Electronic And Chemical Structure Using X-ray Spectroscopies

Performance of semiconductor devices not only depends on the characteristics of bulk materials,but alsothe electronic and chemical structure of relevent interfaces.X-ray spectroscopies are powerful techniques in characteriting properties of materials and interfaces information such as material structure,element composition,chemical state,chemical bonds.Such knowledge is critical for revealing the key factors that limit performance of the semiconductor devices,and play important roles for devices optimization and study the unique physical phenomenon on the interfaces.Silicon carebide(SiC)shows wide band gap,high carrier mobility and good chemical stability,and is a promising semiconductor material for various applications(e.g.,electron devices suitable for harsh environment).Zinc oxide(ZnO)is a promising semiconductor material for optoelectronic applications,due to its wide direct bandgap and large exciton binding energy.This thesis focuses on study the electronic and chemical structure of silicon carbide and zinc oxide,using x-ray spectroscopies,and its influence on the device performanc.In this thesis,ZnO/CIGSe heterojunctions were prepared by chemical vapor deposition and a-SiC/AZO heterojunction were prepared by radio frequency magnetron sputtering.The structures of thin films were studied by scanning electron microscopy(SEM)and X-ray diffraction(XRD).X-ray photoelectron spectroscopy(XPS),X-ray excited Auger electron spectroscopy(XAES),and synchrotron-based X-ray absorption spectroscopy(XAS)yield the electronic chemical structureIt is discovered that the morphology of ZnO can be tuned by deposition parameters,such as substrate temperatures.Anisotropic ZnO rod-like structures were obtained at a higher substrate temperature.The ZnO rods are terminated by the oxygen ions on the top,while the side wall surface enriched with the Zn ions.Furthermore,it is found that not only Si-C bonds but also Si-Si bonds and silicon oxides exist at the a-SiC/AZO heterojunctions,.Near the interface,larger amount of silicon present in the higher oxidation state,while silicon in the thin film possess with lower oxidation state.This is likely due to abundance of O from AZO substrate and sufficient energy provided by the magnetron sputtering process.Furthermore,annealing process might lead to increase of silicon oxides at the interface and in the thin film.Such results are useful for optimization of ZnO/CIGSe and a-SiC/AZO heterojunction,and provide necessary support for integrating SiC and ZnO with other semiconductor materials.