Abnormal electrical behavior and phase changes in implanted p⁺- And n⁺-Si channels under high current densities

The p⁺- and n⁺-Si channels were prepared by implanting a dose of 5 × 10¹⁵ ions/cm² of BF⁺₂ and As⁺ at 40 keV, respectively, into the n-Si and p-Si substrates, followed by a 900°C-30 min annealing. Nickel contacts (cathode and anode) to these channels were electron-gun evaporated. Electrical current was applied gradually to 80 mA to these channels, corresponding to current densities of 10⁶-10⁷ A/cm². For the p⁺-Si, the resistance responded by increasing to a maximum, then decreasing until a precipitous drop took place. For the n⁺-Si, the resistance increased by a less amount compared to the p⁺-Si, but also dropped abruptly. The resistance drop is permanent in the p⁺-Si channels, but not in the n⁺-Si channels. Mechanisms responsible for these resistance changes in terms of Joule heating, high field effect and junction leakage are proposed. For the precipitous drop in channel resistance of the p⁺-Si, scanning electron microscopy and transmission electron microscopy showed that a NiSi₂ line bridging the cathode and anode contacts had been formed. No silicide line formation in the n⁺-Si channels was observed.