| The scope of this work is to determine the effect of ion implantation on the minority carrier lifetimes of upgraded metallurgical grade (UMG) silicon solar cells. Two species of atoms, arsenic and antimony, are used to getter impurities on P doped UMG wafers. The lifetimes of these wafers are measured before and after the implant process and after various annealing sequences using photoconductivity measurements provided by a Sinton WCT-120. Devices are then fabricated on these wafers so that lifetime trends measured by photoconductivity can be verified by reverse recovery time transient and quantum efficiency techniques. Ultimately, minority carrier lifetime measurements allow determination of the combination of implant species and annealing techniques that best increase the minority carrier lifetimes of the UMG wafers. Both arsenic and antimony implants proved capable of increasing minority carrier lifetime by a factor of ten. |
