The effect of palladium deposition on electrically active defects in irradiated silicon

Abstract

DLTS was used to study the effect of resistive physical vapour deposition of Pd Schottky contacts on the defects observed in an n-type Si substrate that was irradiated before deposition (“pre-irradiated”) and compared to defects in a diode that was irradiated after deposition (“post-irradiated”). In the post-irradiated samples, the familiar radiation-induced defects were observed. However, in the pre-irradiated samples, 13 new defects were observed, with DLTS signatures differing from those of the defects in the post-irradiated diodes.

Out of the 13 newly observed defects, four defects, with activation energy of 0.180, 0.220, 0.360 and 0.607 eV, had DLTS signatures corresponding to defects previously observed in Pt-containing Si, while no match was found for other defects.

The effect (referred to as the Pd Effect) was carefully studied, and it was found that the effect was only observed with Pd, and not when other metals including Au, Ni, Al, Ag were used. Careful experiments ruled out annealing during evaporation of the contact as a possible cause. Different sources of Pd were used in un-used crucibles in an attempt to avoid contamination, but the effect was observed in all cases.

It was found that this phenomenon was inhibited by the presence of a thin intermediate layer, irrespective of the layer being Pd or Au. We therefore conclude that the effect is only observed when Pd is deposited directly on the irradiated Si surface.

We believe that these defects are produced by defect-enhanced diffusion of Pd. Overall, the study enhances our understanding of defect behaviour in silicon-based devices, particularly under irradiation and metal deposition conditions, and reveals the unique properties and effects of Pd.