Crystal Defect Evolution And Electrical Properties Of Polycrystalline Metallurgy

As a new method to produce solar grade silicon,metallurgical method has the advantages of low cost,low energy consumption,moreover,industrial silicon could be directly purified to be to solar grade silicon when adopting metallurgical method.Whereas,large amount of crystal defects will be generated in multicrystalline silicon(MC-Si)obtained by metallurgical method,which would exert serious effect on the electrical properties of MC-Si.Consequently,conducting researches investigating the elimination of crystal defects and its evolution trend will exert significant influences on improving the electrical properties of MC-Si.Purified metallurgical grade MC-Si with high phosphorus ingot was obtained with the method of directional solidification technique,both the evolution of crystal defects and the variation of the electrical properties were discussed in this research under rapid thermal annealing and conventional thermal annealing with the temperature of 800??1300? and the holding time of 30s?10h.The variation of dislocation defects,grain size,grain boundaries and the crystal orientation of MC-Si were characterized before and after annealing treatment,and the electrical properties of MC-Si which were caused by the change of crystal defects were also analyzed,obtaining the evolution of the crystal defects,the variation of minority carrier lifetime as well as the resistivity of MC-Si under different annealing conditions.During the process of rapid heat treatment,the experiment of different annealing conditions has been investigated that the dislocation density decreased obviously with the temperature rises from 800? to 1200 ?;The elimination of dislocation of the MC-Si almost the same with the holding time increased from 30s to 120s,there is no significant influence on the elimination of dislocation in MC-Si;The grain sizes of MC-Si could increase by 45800?m2 at most under the annealing condition of 1100?-120s;The amount of misorientation of 1.5° and 59.5° changed largest after annealing,and also the crystal orientation of MC-Si will not vary under different rapid thermal annealing conditions.The most obvious enhancement temperature of minority carrier lifetime and resistivity appears at 1200?,which could increase by 0.189?s and 0.034?·cm respectively.In the process of conventional heat treatment,the density of dislocation defects decreased significantly with the temperature rises,and it will achieved the best elimination effect at the temperature of 1300?,which similar to the phenomenon of rapid heat treatment;And after the annealing time extended from 2h to 10h,the dislocation density of MC-Si reduced more obvious;The EBSD test results of MC-Si wafers showed that,the grain size of MC-Si increased by 42300?m2 after annealing process,and the biggest variation of grain boundaries were also the misorientation of 1.5° and 59.5° in quantitative terms,especially after 10h preservation at 1300C,the misorientation of 1,5° increased by 13%,and the misorientation of 59.5° reduced by 9.44%after annealing;The crystal orientation of MC-Si will not vary under different conventional annealing process,too;The resistivity of MC-Si wafers improved obviously after 10h preservation,and the resistivity increases by nearly 30%from bottom to top of the silicon ingot,the maximum value could increase by 0.22?·cm.The minority carrier lifetime and resistivity of MC-Si would improve significantly under the interaction of the decrease of dislocation defects density,the increase of grain sizes,the adsorption of impurities by grain boundaries and the mutual integration of impurities inside the grain,which increased by 0.23?s and 0.22?·cm respectively.