Papers by Author: Zheng Tang Liu

Abstract: Structural, electronic and optical properties of S-doped anatase TiO₂ have been investigated using the first-principles density-functional theory. The band structure and density of states show that the band gap of anatase TiO₂ narrows due to the presence of the S-3p energy level in the top of the valence bands. Compared with the optical absorption edge of the undoped anatase TiO₂, the optical absorption edge of S-doped anatase TiO₂ shifts to a lower energy, which indicates that S-doped anatase TiO₂ can be used for visible-light absorption applications.

Abstract: The GaAsP crystal material grown on GaAs substrate has been extensive applications in the area of photoelectronic device. There because GaAsP have advantageous photoelectronic performance and adjustable band gap. We report growth of GaAs1-xPx grown on GaAs substrate by solid source molecular beam epitaxy (SSMBE). On the basis of the optimized Ⅴ/Ⅲ flux ratio, appropriate growth rate, and the substrate temperature for sample growth, different composition GaAs1-xPx layers had been grown on GaAs top. Lattice-mismatched became the big challenges to high-quality epitaxial growth of the GaAs1-x Px materials on GaAs substrate. The crystalline quality, surface morphology were performed by applying high resolution X-ray diffractometry (HRXRD) and high resolution optical microscopy. The etched region and internal defect were also investigated.

Abstract: CuAlO₂ is an important p-type transparent conductive oxide (TCO) material. Thus, in this paper, the structure and properties of 2H-CuAlO₂ are calculated using the plane-wave ultrasoft pseudopotential technique based on the first-principles density functional theory. The calculated equilibrium lattice parameters is in good agreement with experimental and reported values. The energy band gap of 2H-CuAlO₂ has been calculated and the results shows that 2H-CuAlO₂ has an indirect band gap. The density of state for 2H-CuAlO₂ has also been calculated.

Abstract: HfO₂ thin films were prepared by radio frequency (RF) magnetron sputtering at different RF powers. The influence of RF power on optical properties of HfO₂ thin films were investigated by spectroscopic ellipsometry (SE) toghther with high-resolution transmission electron microscopy (HR-TEM) and Fourier transform infrared spectroscopy (FTIR). The results show that there is a SiO₂ interface layer between HfO₂ thin film and Si substrate. A four layer structured model consisting of SiO₂ interfacial layer was used to fit the SE data. With the increasing RF power, the refractive index of the HfO₂ thin films increases firstly and then decreases and, the extinction coefficient of the HfO₂ thin films increases little.

Abstract: The electronic properties of N-doped orthorhombic SrHfO₃ have been calculated using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory with the local density approximation. From the calculated band structure and density of states, the bandgap reduction is observed due to the presence of the N-2p states in the top of valence bands, which leads to red-shift. Moreover, in order to clarify the charge transfer and bonding properties of N-doped orthorhombic SrHfO₃, we have calculated and analysed the charge density.

Abstract: Electronic structure, effective masses and optical properties of monoclinic HfO₂ were studied using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT). The calculated equilibrium lattice parameters are in agreement with the previous works. From the band structure, the effective masses and optical properties are obtained. The calculated band structure shows that monoclinic HfO₂ has indirect band gap and all of the effective masses of electrons and holes are less than that of a free electron. The peaks position distributions of imaginary parts of the complex dielectric function have been explained according to the theory of crystal-field and molecular-orbital bonding.

Abstract: Structural, electronic and optical properties of 2H-CuAlO₂ were computed, using the plane-wave ultrasoft pseudopotential technique based on the first-principles density functional theory (DFT). The equilibrium lattice parameters, band structure, densities of states (DOS) and charge densities of 2H-CuAlO₂ have been obtained. The equilibrium lattice parameters, band structure and DOS are found to be in good agreement with the available experimental and calculational values. The charge densities and the chemical bonding of 2H-CuAlO₂ are analyzed, which show that bonding between Cu and O is mainly covalent due to Cu 3d and O 2p hybridization and that bonding between Al and O is mainly ionic. The complex dielectric function, refractive index and absorption coefficient of 2H-CuAlO₂ have been predicted. The calculated static dielectric constant and static refractive index of 2H-CuAlO₂ is 7.1 and 2.66, respectively.

Abstract: We have performed ab-initio total energy calculations using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT) to study structural parameters, electronic structure, chemical bonding and optical properties of orthorhombic Li₂BeSiO₄. The calculated lattice parameters are in agreement with experimental data. The band structure shows a direct band gap. From the DOS analysis, charge densities and population analysis, electronic and chemical bonding properties have been studied. Furthermore, in order to understand the mechanism of optical transitions of orthorhombic Li₂BeSiO₄, the complex dielectric functions are calculated and analysed.

Abstract: Germanium carbon films were prepared on ZnS substrates by reactive RF magnetron sput- tering of a Ge target in Ar and CH4 mixtures for IR antireflective and protective purposes. IR transmit- ttance spectra of the specimens were measured, with which H content in the films was investigated. The C and Ge contents and the atomic binding state were studied by X-ray photoelectron spectroscopy. The results show that H involved in the films combine mainly with C at low substrate temperatures. IR absorption peaks caused by the C-H bonds decrease with increasing temperature, indicating the drop of the C-H bonds content in the film. At relatively low temperature the film is high in C content and low in refractive index; at high temperature the film is low in C content and high in refractive index. Both C-Ge and C-C bonds exist in the film and O impurity combines mainly with Ge.

Abstract: The convex surface of the infrared dome is exposed to the harsh environment of the outside world, and therefore requires a coating which not only increases transmission but is able to withstand rain erosion so as to enhance system performance. This paper deals with the techniques that were developed to deposit a uniform thick SiO2 coating for sapphire dome by radio frequency magnetron sputtering. Results show that average transmission increment in wavelength range from 3 to 5um for the sapphire dome coated on convex surface was more than 4.0%. The transmission non-uniformity over the convex surface of the coated sapphire dome was less than 1.7%.