| Due to the direct band gap,the gap width matched with the solar spectrum and highlights absorption coefficient etc,III-V nanowires(GaAs NWs)absorption efficiency and photoelectric conversion efficiency is no worse than thin film materials,and the photoelectric conversion efficiency of single root GaAs nanowires(40%)breaks through the theoretical limit of single section solar cells(30%),so the unique advantages of GaAs nano wire solar cells will have broad prospect of application in the field of solar energy development in the future.But the high cost and complex process of the materials growth and the preparation of device makes the GaAs industrialization of nanowire solar cells very limited.Therefore,it is necessary to reduce the experimental cost and improve the quality of GaAs nanowires crystals.It is of great significance to adopt the simple growth process synthesis the high crystalline GaAs nanowires with high switch ratio and carrier mobility.Based on the study of III-V nanowire semiconductor materials,the growth of GaAs nanowires was studied by chemical vapor deposition(CVD)using solid-state source;The relationship between catalyst of different kinds and particle size and the growth of III-V nanowires were discussed;In the end,the novel Ga-GaAs nanowire heterostructure was successfully prepared by the regulation of experimental conditions,and a breakthrough was made in the material structure,which was better applied in the research of solar cells.The research contents and experimental results of this thesis are composed of the following parts:(1)The cubic,octahedral and dodecahedral Au particles and Au@Pd core-shell nanoparticles were synthesized to replace the catalyst of thin film annealing pellet makes the catalyst particle size distribution more uniform.The CVD method was used to explore the effect of different morphology catalysts on the growth of nanowires.By analyzing the morphology of the nanowires,it can be found that the catalyst of different morphology has great influence on the structure morphology of nanowires,this may be related to the surface energy of Au particle catalyst with different morphology,and Au cubes catalyze the growth of nanowires with poor morphology;For the NWs of the octahedral catalytic growth of Au@Pd,the texture is smooth but the particle size is not uniform,which may be related to the Au/Pd ratio dissolved in the catalyst.(2)Different NWs were grown by different catalyst nanoparticles such as Pd Ag Ni and Au,including InGaAs GaAs and GaSb NWs.In order to measure controlled by the solubility of catalyst and extension process of the growth of the III-V NWs.The results of the study clearly proved that the small diameter of catalyst with high solubility Ga seeds can make single crystal grow faster,and more inclined to grow in the direction of the<111>.In contrast,the large diameter catalyst with lower Ga components catalyzed the growth of nanowires with slow growth rate and many defects in NWs growth and even a lot of bending.The related mechanism can be explained by the epitaxial growth of NWs under the VSS mechanism.(3)By using CVD system in accordance with the growth mechanism of VLS.Through controlling the evaporation temperature,the length of the Ga segment nanowires was successfully controlled.This means that the generation of Ga segment nanowires is determined by the equilibrium between the diffusion and precipitation process of Ga from the Au-Ga alloy and the precipitated Ga and As vapor reaction.More importantly,this Ga-GaAs nano wire heterostructure has a high schottky barrier(?0.8 eV)on the interface between Ga and GaAs NWs,which is attributed to the effect of surface Fermi level.All of the results show that the controllable synthesis of Ga-GaAs NWs heterostructure has a strong application prospect for schottky type devices in the future,also has a strong application value in solar cells. |
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