Research On Crystal Growth And Defects And Impurities Of High-purity Multicrystalline Silicon Produced By Metallurgical

Nowadays,the multicrystalline silicon producers and researchers in many countries are doing some researches on the new technologies to produce solar grade multicrystalline silicon.Among of them,the technology to produce multicrystalline silicon by metallurgy is mostly received.While exist of defects and impurities greatly decrease the cell translation efficiency and interaction between impurities and defects, especially the interaction between metal impurities and defects.In this thesis,we using the scanning electron microscope(SEM),electron back-scattered diffraction(EBSD),X-ray diffraction analysis(XRD),energy spectrum analysis(EDS)and optical microscope to do systemic research on multicrystalline silicon which obtained by vacuum-metallurgical technology,which including the impurity and the defect and the characteristic of crystal growth of multicrystalline silicon.Besides,it is including the annealing characteristic of multicrystalline silicon with argon atmosphere.In multicrystalline silicon,XRD patterns show that the preferred orientations are <111> and <422> which under condition V₁.EBSD images indicate that the texture of the same sample was <111>{111},the intensity are grade seven,what is more,there is also has another texture in orientation <112> and the intensity is grade five.The misorientation angle of orientation <111> is 60 degree,which account for 40%.The maximum grain size is 115μm,and more than 90%grain's size is more than 100μm, the minimum grain size is nearly 25μm.High intensity dislocations and all sorts of grain boundaries are exist in the multicrystalline silicon which obtained by vacuum-metallurgical technology from metallurgy grade silicon.Small-angle grain boundary account for 1.2%,others grain boundaries are composing of coincidence structure lattice,which including twin grain boundaries∑3,∑1,∑7,∑9,∑11 and∑17b.There also are many defects exist in multicrystalline silicon,just like dislocation,and these dislocations would reacted with each other then form to fault.After etching,we found that etched surface of <110> is triangle,and surface <111> is looks circle.All these defects will arouse segregation of metal impurities,and will produce impurity contain,and lead to micro-holes.In addition,annealing was adapted to treating multicrystalline silicon piece by tube type resistance furnace,XRD analysis of silicon piece is revealed that 4 hours heat preservation at 800℃and then cooling naturally can enhance the texture orientation <111>,also can decrease the micro-holes of the surface.