Wide Band Gap Semiconductor Sic And Of Zno Using Synchrotron Radiation Photoelectron Spectroscopy Study

The third generation semiconductors including SiC and ZnO, which are called wide-bandgap semiconductors, express some useful properties such as wide band gap, good chemical stability, excellent thermal conductivity. As a result, they are regarded as the most potentially candidates for the next generation opto-electronic and micro-electronic devices with high power and high frequency as well as working in high temperature environment. As an effective method to investigate the electronic structures of various materials, the synchrotron radiation photoelectron spectroscopy (SRPES) has been widely used to study the band structures, the electronic states of surface and interface of semiconductor materials. The research of such wide-bandgap semiconductors by the method of SRPES is very important not only for the fundamental research, but also in the field of semiconductor device manufacture.In this thesis, by using the equipment of the experimental stations of National Synchrotron Radiation Laboratory (NSRL) and Singapore Synchrotron Light Source (SSLS), the researches have been done to investigate the band structures, band dispersing, surface reconstruction, surface polarity, surface absorption, metal-semiconductor interface and local structure of defect states induced by semiconductor doping with the method of SRPES and the first principle full potential linear augmented plan wave (FP-LAPW) method. The major results are listed as the following:1. The electronic structure of 6√3×6√3 R30°reconstructed surface of 6H-SiC(0001) have been investigated by the method of synchrotron radiation angle-resolved photoelectron spectroscopy (SRARPES) and FP-LAPW method. From the normal emission spectra, we obtain the bulk energy band structure and find three surface states. The bulk energy band structure measured by experiment agrees well with the theoretical calculation result. From the off normal emission spectra, the surface state dispersion is measured along (?), the high symmetry lines of the surface Brillouin zone. The results show that only surface state So shows expected periodicity of 6√3×6√3 R30°reconstruction in all probed SBZ. According to the experimental results, we conclude that surface state So should be attributed to the C-C dangling bonds of the surface reconstruction. While surface states S₁ should be attributed to the unsaturated C dangling bonds.2. SRPES and X-ray Photoelectron Spectroscopy (XPS) have been used to study the growth mode of Mn on the 6H-SiC(0001) surface and Mn/6H-SiC(0001) interface in situ. The experimental results show that the early growth mode at room temperature is considered to be 2D layer by layer mode. With increasing the coverage of Mn, the surface reflects a clear metallic characteristic. During the deposition, Mn is quite stable on the SiC surface, a downward movement of Fermi level in band structure measurement is observed and the resultant Schottky Barrier Height (SBH) is calculated to be about 1.79 eV. When the deposition amount reaches 2nm, annealing the sample at 250℃will induce Mn diffusion into the SiC substrate with no chemical reaction. Further annealing at 500℃, there will form some Mn silicide at the interface.3. The C₆₀/Si(111) interface and the formation process of SiC upon annealing have been investigated by using SRPES. C₆₀ molecules are chemisorbed on the Si(111) surface at room temperature via Si-C₆₀ hybridization with covalent bonds. After annealing the sample, the Si-C₆₀ hybridization weakens C-C bonds internally in C₆₀ molecules and enhances the formation of Si_xC₆₀,an intermediate species. Further annealing up to 650℃leads to the decomposition of C₆₀ molecules, the released carbon fragment will bond with external silicon atoms to form SiC. After annealing the sample to 850℃,decomposition of all C₆₀ molecules is accomplished and all decomposed carbon atoms will bond with the silicon atoms of substrate to form SiC. The sample surface is fully covered with SiC film.4. The electronic structure and surface state dispersion of the ZnO(000(?)) surface have been investigated by SRARPES and FP-LAPW method. From the normal emission spectra,we obtain the bulk energy band structure along theΓA direction and find two surface states. The bulk energy band structure measured by experiment agrees well with the theoretical calculation result. From the off normalemission spectra, the surface states dispersion is measured along (?), the high symmetry lines of the surface Brillouin zone. According to the comparison between experimental results and theory calculation, we conclude that these two surface states are originated from the back-bonds of Zn4s-O2p mixing states and the back-bonds of p-p (or p-d) mixing states.5. By employing the X-ray photoelectron diffraction (XPD) method and the XPD theory based on the single scattering cluster-spherical wave (SSC-SW) model, we have studied the surface polarity of the ZnO film. With the different constant emission polar angles, we obtain the photoelectron diffraction curves about the Zn 2p_3/2 XPS intensity as a function of the emission azimuth angle. Comparing the experimental results with the calculated results of ZnO (0001) andZnO(000(?)) polar surfaces by the method of SSC-SW, we can conclude that the ZnO film is terminated with (000(?)) polar surface. Combined with atomicstructure model of ZnO (000(?)) polar surface, we have elucidated the origin of diffraction enhanced peaks from the photoelectron diffraction curves.6. By employing the Full Potential Augmented Plan Wave and Local Orbital method (APW+LO), we have studied some possible hydrogen-related defect sites in ZnO. In view of the calculated defect formation energy, the most possible defect site should inhabit BC// local structure position.But the calculated local vibrational modes (LVMs) of defect sites, when comparied with the infrared absorption (IR) result, lead to the conclusion that the hydrogen-related defect sites in ZnO can inhabit both BC// and ABo// local structure positions.