Study On Electrical Properties Of Defects Related To Seed Misorientation In Quasi-Mono Crystalline Silicon

Quasi-single crystalline(QSC)silicon is a potentially ideal candidate material for Si-based solar cells.It combines low manufacturing cost with high conversion efficiency that is close to that of Czochralski(Cz)silicon.However,crystallographic defects related to seed misorientation including dislocations and sub-grain boundaries(sub-GBs)appearing in QSC silicon are detrimental to the performances of its solar cells.Up to now,the research on these two kinds of defects mainly concentrate on Cz silicon and multi-crystalline silicon.Thus,it is highly desirable to systematically investigate the electrical properties of crystallographic defects in QSC silicon.In this thesis,by combining electron beam induced current(EBIC)and deep level transient spectroscopy(DLTS),the recombination activity of crystallographic defects in QSC silicon were systematically studied.The influences of Fe contamination and phosphorus gettering(PG)on recombination activity of defects were also investigated.The innovative achievements have been listed as follows.(1)There are three kinds of defects in QSC silicon,e.g.,the scattered dislocations,the dislocation arrays(DAs)and the sub-GBs.The dislocation-related defects and sub-GBs can cause energy levels at Ec-0.53 ev and Ec-0.17 ev,respectively.The scattered dislocations show low recombination activity.However,the recombination activity of DAs exhibits an increase trend with the increase of dislocation density.There is a positive correlation between misorientation and recombination activity of sub-GBs<0.7°.The sub-GBs with the misorientation>0.70°show constant EBIC contrast at room temperature.(2)In the as-grown QSC silicon samples,the DAs and the sub-GBs<0.70°show significant difference in EBIC contrast,which dramatically decrease after Fe contamination.For the sub-GBs>0.70°,there is no significant change in EBIC contrast before and after Fe contamination.The Fe contamination causes three energy levels at E,v+0.41 ev,Ev+0.47 ev and E,v+0.31 ev,respectively.The corresponding capture cross sections are 9.31 x 10-14 cm-2,5.84x 10-14 cm-2 and 2.23x 10-15 cm-2,respectively.(3)After PG,the DAs exhibit an EBIC contrast(300 K)of less than 10%,with low recombination activity.However,the sub-GBs with a misorientation of>0.7°still maintain strong EBIC contrast and deep level characteristic.Therefore,this kind of sub-GBs has the largest influence on the performances of solar cells,and the DAs would not play important role in the degradation of QSC silicon solar cells.