Influence of different surface treatments on multicrystalline silicon wafers for defect characterization by LBIC

Abstract

In this paper, we investigate the influence of different chemical treatments on the surface of multicrystalline Silicon (mc-Si) wafers, for both revealing grain boundaries and intra-grain defects. Electrical characterization by light beam-induced current (LBIC) was also carried out after the treatments. Several pieces of *2 9 2 cm 2 , from mc-Si wafers, were mechanically polished and chemically etched and subsequently metallized with gold (on both surfaces) by sputtering, using optimized deposition times for doing transparent electrodes suitable for LBIC mapping. The surface treatments are discussed in terms of their capabilities to reveal the crystal defects and to provide the best conditions for efficient LBIC signals directly on silicon substrates, in the absence of a p-n junction. The best surface treatments allowing both revealing crystallographic defects and permitting the measurement of highly contrasted LBIC maps is the KOH etching. A large number of intra-grain defects are clearly revealed, being their electrical activity sensitively higher than that of the grain boundaries.

Characterization of deep level defects present in mono-like, quasi-mono and multicrystalline silicon solar substrates

“…Finally, 90 nm thick and semitransparent 18 nm thick gold layers were created by sputtering. The thinner layer should be transparent enough to let the excitation light pass through it for LBIC characterization [6]. The result is a sandwich structure with a double junction that allows us to use both bias polarizations.…”

Residual Strain and Electrical Activity of Defects in Multicrystalline Silicon Solar Cells

“…The surface of sliced mc-Si wafers does not permit to extract clean Raman information; therefore, surface preparation is necessary in order to obtain the Raman spectra free of the inuence of the surface. In a previous work [8], we investigated dierent chemical etchants of polished mc-Si wafer, KOH etching was seen to be quite sensitive to reveal the GBs. After this GB revelation, the samples were metallised with semi--transparent gold layers on both faces for LBIC measurements; the GBs were shown to give very low LBIC contrast, concluding that the GBs themselves are not the main electrically active defects in mc-Si; on the other hand, a large number of intra-grain defects were revealed in the LBIC maps, accounting for its large electrical activity [8].…”