Abstract
Experiments of deep-level transient spectroscopy and transmission electron microscopy (TEM) observations have been carried out on heat-treated Σ=25 silicon bicrystals precontaminated with nickel before being heat treated at various temperatures Ta. For the lowest Ta value (600 °C), the electronic interface states were found to be shared between two overlapping narrow continua around Ec−0.63 eV and Ec−0.52 eV. Upon increasing Ta, these states shift toward shallow positions and exhibit a marked tendency to shrink and to turn into a unique trap level. While the annealing at 900 °C has led to a single state at Ec−0.50 eV, this later moved to Ec−0.48 eV for 1000 °C and then to Ec−0.44 eV for 1100 °C, with an accompanying consistent lowering in the barrier height (BH). TEM observations demonstrated the formation of pure type-B NiSi2 platelets for 800 °C, but indicated an increasingly important growth of type A for increasingly higher Ta values. While the existence of a unique trap level at high Ta could be explained, like previous findings, by some ‘‘uniform’’ coverage of the boundary by the precipitates, the displacement of the interface state(s) toward shallower positions, together with the reduction of the potential barrier, are interpreted in terms involving the increasing contribution of A-type plates with their low BH in addition to that of B-type silicides with their high BH.