Ultrafast PBTI characterization on Si-free gate last Ge nFETs with stable and ultrathin Al2O3 IL

This work for the first time reports positive bias temperature instability (PBTI) on Ge n-channel metal oxide semiconductor field effect transistors (nFETs) with a stable and ultrathin (5 Å) Al₂O₃ inter layer (IL) using ultrafast (~μs) characterization techniques. Since ~μs delay time is employed, all possible signatures of trap generation and trapping are captured. Trap generation behavior is studied using a detrapping technique that is shown to predict (1) threshold voltage degradation (ΔV_T) time exponent (n) independent of gate oxide field and (2) trap-generation signature at IL/high-κ interface. This is the first report of such a signature in Ge nFETs. PBTI is shown to improve with decrease in high-κ thickness, increase in IL thickness and forming gas annealing. Deconvolution of uncorrelated IL/high-Λ interface trap and high-κ bulk trap components from ultrafast data using a compact model shows a stable IL/high-κ interface.