Piezoresistance in defect-engineered silicon

The steady-state, space-charge-limited piezoresistance (PZR) of defect-engineered, silicon-on-insulator device layers containing silicon divacancy defects changes sign as a function of applied bias. Above a punch-through voltage (\(V_t\)) corresponding to the onset of a space-charge-limited hole current, the longitudinal \(\langle 110 \rangle\) PZR \(\pi\)-coefficient is \(\pi \approx 65 \times 10^{-11}\)~Pa\(^{-1}\), similar to the value obtained in charge-neutral, p-type silicon. Below \(V_t\), the mechanical stress dependence of the Shockley-Read-Hall (SRH) recombination parameters, specifically the divacancy trap energy \(E_T\) which is estimated to vary by \(\approx 30\)~\(\mu\)V/MPa, yields \(\pi \approx -25 \times 10^{-11}\)~Pa\(^{-1}\). The combination of space-charge-limited transport and defect engineering which significantly reduces SRH recombination lifetimes makes this work directly relevant to discussions of giant or anomalous PZR at small strains in nano-silicon whose characteristic dimension is larger than a few nanometers. In this limit the reduced electrostatic dimensionality lowers \(V_t\) and amplifies space-charge-limited currents and efficient SRH recombination occurs via surface defects. The results reinforce the growing evidence that in steady state, electro-mechanically active defects can result in anomalous, but not giant, PZR.