EXAFS studies of arsenic in amorphous silicon

Extended X-ray absorption fine structure measurements were used to determine nearest neighbor coordination numbers and distances for As in amorphous Si prepared by 100 keV As ion-implantation of single crystal Si. In the limit of low As concentration, the average AsSi coordination number was 3.2±0.1 and the As-to-Si distance was 2.37±0.02 A ̊, compared with 4 and 2.41±0.02 A ̊, respectively, for As in crystalline Si. It is concluded that 20% of the As atoms are fourfold coordinated and 80% are threefold coordinated in the amorphous Si, and that the lack of electrical doping by the fourfold coordinated As results from electron trapping by dangling bonds or other structural defects. © 1992.