Investigations On Epitaxy Of Low Defect-Densitv SI-based Gallium Arsenide Material And Surface Anti-reflection Of Relevant Materials

High-performance,low-cost optoelectronic devices promote the development of new optoelectronic devices in the direction of integration and miniaturization.Silicon-based optoelectronic integration and surface plasmon optics have become important research fields in the development of information technology.The information industry has higher and higher requirements on the speed,function and power consumption of integrated circuits.Among them,silicon-based optoelectronic integration technology is a fundamental basis for ultra-high-speed,ultra-low loss optical interconnect technology.Si is an indirect bandgap material that does not have good light-emitting properties.It is hoped that Si-based Ⅲ-Ⅴ semiconductor lasers will solve the problem of Si-based light sources.Therefore,it is necessary to obtain low-defect-density epitaxial layers of Ⅲ-Ⅴ semiconductor materials on Si substrates.There are differences in physical properties such as thermal expansion coefficient,lattice constant,and polarity between Si substrate and GaAs epitaxial materials,resulting in defects on GaAs epitaxial layers such as thermal cracks,threading dislocations,and anti-phase boundaries formation.These defects seriously affect the crystal quality of epitaxial layers.After years of research,some solutions have been found to solve these problems,such as three-step method,selective-area growth and buffer layer.However,the defect density of GaAs epitaxial layer is still high,which needs further research.The surface plasmon resonance of metal nanoparticles makes them have strong absorption properties in the spectral regions of near ultraviolet and visible light.Adding metal nanoparticles into solar cells and utilizing their surface plasmon resonance to achieve thin-film and high-efficiency devices has attracted a large number of researchers.Surface plasmons can be used in any type of photovoltaic cell,which can improve the absorption efficiency of light.With high power conversion efficiency and low manufacturing cost,Cu(In,Ga)Se2(CIGS)thin film solar cells are one of the most promising photovoltaic cells in the future.However,the incident light will be affected by the Fresnel reflection on the surface of the solar cells window layer,which will lead to a decrease in photogenerated current.Applying metal nanoparticles to the preparation of CIGS solar cells may significantly improve the anti-reflection ability of the material surface.The research of this paper focuses on the epitaxy of Si-based GaAs materials and surface anti-reflection of semiconductor materials,its main research contents and academic achievements are as follows:(1)The distribution of thermal stress for GaAs grown on V-groove patterned Si substrates is investigated by the finite-element method.Results show that compared with the planar substrate,the average thermal stress is significantly reduced for the GaAs layer on the patterned substrate.At the same time,the effect of the width of the V-groove,thickness and width of the SiO2 mask on the thermal stress distribution is studied.The results indicate that when the width of V-groove is 50 nm,the width and thickness of the SiO2 mask are both 100 nm,GaAs layer is subjected to the minimum thermal stress.Furthermore,compared with the planar substrate,the average thermal stress of the GaAs epitaxial layer in the growth window region of the patterned substrate is reduced by 90%.These findings are useful for growing high quality GaAs films on patterned Si substrates.(2)The blocking effect of the different Si-based InGaAs/GaAs superlattice structures for dislocation was investigated using finite element method.Firstly,the thickness of the superlattice and the number of cycles of the superlattice structure were studied,and their effects on the effect of suppressing threading dislocations are analyzed.The results show that in the sample area of a single threading dislocation(a square area corresponding to a specific threading dislocation density,with an area exactly equal to the area occupied by the average single threading dislocation),the farther the threading dislocation is from the geometric center,the easier it is to be blocked.As far as a single superlattice unit is concerned,the dislocation blocking rate of 9 nm In0.15Ga0.85As/10 nm GaAs superlattice is the highest.When the strained superlattice has a constant period,the blocking rate of a single superlattice unit for dislocations decreases with the increase of the unit number along the growth direction.As the period of the strained superlattice increases,the dislocation blocking rate of the strained layer at the bottommost layer increases.For GaAs epitaxial layer with a thickness of 100 nm grown using a three-step method,when the period of 9 nm In0.15Ga0.85As/10 nm GaAs is 3,it can block 39.1%of the threading dislocations propagation.This provides theoretical support for using superlattice structures to reduce the dislocation density of GaAs/Si.(3)The surface phase regulation of non-offset Si(001)substrates by hydrogen annealing was investigated by experiment and simulation using density functional theory.Simulations show that when the hydrogen chemical potential is in the range of-4.02 eV to-3.79 eV,the Si(001)surface is more likely to form steps with double atomic layers.Experiments show that when the hydrogen annealing temperature and time are 800℃(the hydrogen chemical potential is-3.87 eV)and 10 min,respectively,the surface of the GaAs epitaxial layer grown on the non-offset Si(001)substrates have no antiphase boundaries.(4)Anti-reflection coatings(ARCs)with double-layer metal nanoparticles for CIGS solar cells were proposed.A study of three ARCs nanostructures(Ag-SiO2-Ag,Au-SiO2-Au and Au-SiO2-Ag structures)on CIGS solar cells was presented using the finite time-domain difference method.Various ARC nanostructures with different metals(Au and Ag),metal nanoparticle radius,spacing layer(SiO2)thickness and the period(corresponding to the particle density)on CIGS solar cells were systematically optimized.The simulation results show that among the three ARCs nanostructures mentioned above,the Au-SiO2-Ag structure has the best performance,and among the selected parameters.Moreover,the AuSiO2-Ag structure was demonstrated to have the lowest reflection intensity when the thickness of the SiO2 layer is 45 nm,the radius of the metal particle is 14 nm,and the side length of the period is 41 nm.The reflectivity of the CIGS solar cells with the optimal ARCs structure was reduce by 83%compared with the case of no using ARCs.And compared with the MgF2 anti-reflection film,the reflectivity was reduced by 37%.