  Experimental evidence indicating the beneficial impact of a phosphorous
diffusion gettering (PDG) in the reduction of trapping centers is shown, as
observed by means of inductively coupled photoconductance (PC) decay and
lifetime measurements carried out on upgraded metallurgical-grade silicon
(UMG-Si) wafers. The presence of trapping species dominating the long time
range of the PC decay of UMG material (slow traps), which is effectively
removed after a PDG conducted at 780 Celsius, is detected. Notwithstanding, a
second trapping mechanism, characterized by a shorter time constant, still
governs the response at very low injection levels after the gettering.
Furthermore, the beneficial effect of the PDG is studied as a function of
processing time, showing minority carrier bulk lifetime improvements up to
18-fold, up to the range of 70 us. Thereby, the way for developing gettering
strategies capable of successfully removing trap centers and improving the bulk
lifetime of unconventional Si material is paved.
