The β-FeSi2 thin film has been applied in the research field of the solar cell,and the thickness of β-FeSi2 absorption layer was chosen through the experiments.However,Up to now neither the optimal thickness of β-FeSi2 absorption layer nor the relationship between the thickness of β-FeSi2 absorption layer and the solar photo wavelength has been theoretically studied.In this paper,the relationship between the thickness of the absorption layer of β-FeSi2 thin film solar cell and the solar photo wavelength is calculated and analyzed by theory.The results show that the thickness of the absorption layer of β-FeSi2 is at least 200 nm when the optical absorption efficiency of the solar energy reaches 90%,and that the optimal thickness range is from 200 nm to 250 nm,and that the optimal wavelength of the photon absorbed by β-FeSi2 thin film solar cell is from 0.46 μm？0.6 μm.Furthermore,two formulas are put forward to indicate the relationship between the thickness of the absorption layer of β-FeSi2 thin film solar cell and the solar photo wavelength.The thickness of the absorption layer of β-FeSi2 thin film solar cell increases linearly with the solar photo wavelength within the optimal photo wavelength.The formulas provide a reliable theoretical basis of determining the thickness of the β-FeSi2 thin film in the solar cell.
The melting kinetics of bulk SiC is studied by using classical molecular dynamics simulation.The mean square displacement,diffusion coefficient,Lindemann index and non-Gaussian parameter are used to analyze the melt nucleation and macrokinetics in the melting process.Melting occurs when the superheated crystal spontaneously generates many Lindemann particles in which they coalesce together to form melt nucleation inside the crystal.The melting process is similar to the solidification process,but also experiences three processes such as nucleation,growth and relaxation.The melting process can be divided into premelting,accelerated melting and relaxation stages.Using the sectional method can properly reflect the kinetic characteristics of the melting process.
YAN WanJunGAO TingHongGUO XiaoTianQIN YunXiangXIE Quan
A detailed theoretical study of the structural and elastic properties of magnesium silicide Mg2 Si under isotropic lattice deformation has been performed based on the first-principles' pseudopotential method. The results show that isotropic lattice deformation from 94% to 106% results in a linear decrease in the energy gap for the direct Г15-Г1 and indirect Г15-L1 transitions, while the indirect band gap Г15 -X1 increases within a range of 94%-104%, and then reduces over the range of 104%. Additionally, isotropic lattice deformation from 94% to 106% also causes a decrease in the elastic constants and modulus of Mg2 Si. Furthermore, Mg2 Si with lattice deformation from 94% to 106% is brittle, being most brittle at 94% lattice constant.
Semiconducting Mg_2Si films were synthesized on silicon（111） substrates by magnetron sputtering deposition and subsequent annealing in an annealing furnace filled with argon gas,and the effects of heat treatment on the formation and microstructure of Mg_2Si films were investigated.The structural and morphological properties were investigated by X-ray diffraction（XRD） and scanning electron microscopy（SEM）,respectively.The results show that the crystal quality of Mg_2Si films depends strongly on the annealing temperature,the annealing time and the deposited magnesium film thickness.Annealing at 400°C for 5 h is optimal for the preparation of Mg_2Si film. XRD and SEM results show that magnesium silicide film with various orientations is formed on the silicon surface because of the interdiffusion and reaction of magnesium with substrate silicon atoms,and the evolution of surface features on growing films is very dependent on the annealing temperature and time.
A detailed theoretical study on structural,electronic and optical properties of Mg2Si under the isotropic lattice deformation was performed based on the first-principles pseudopotential method.The results show that the isotropic lattice deformation results in a linear decrease in the energy gap for the directΓ15-Γ1 and indirectΓ15-L1 transitions from 93%to 113%,while the indirect band gapΓ15-X1 increases from 93%to 104%and then reduces over 104%.When the crystal lattice is 93%compressed and 113% stretched,the magnesium silicide is a zero-gap semiconductor.Furthermore,the isotropic lattice deformation makes the dielectric function shift and the static dielectric constant change.
CHEN Qian XIE Quan ZHAO FengJuan CUI DongMeng LI XuZhen
Mg films of various thicknesses were deposited on Si（111） substrates at room temperature by resistive thermal evaporation method, and then the Mg/Si samples were annealed at 40 ℃ for 4 h. The effects of Mg film thickness on the formation and structure of Mg2Si films were investigated. The results showed that the crystallization quality of Mg2Si films was strongly influenced by the thickness of Mg film. The XRD peak intensity of Mg2Si （220） gradually increased initially and then decreased with increasing Mg film thickness. The XRD peak intensity of Mg2Si （220） reached its maximum when the Mg film of 380 um was used. The thickness of the Mg2Si film annealed at 400℃ for 4 h was approximately 3 times of the Mg film.
