High Concentration of Interface Traps in MOS Transistor Modeling

Steady-state recombination-generation-trapping of holes and electrons at one-electron neutral traps (charge states 0 and −1) located at the SiO2/Si interface is employed to investigate the effects of high concentration of interface traps on the recombination dc base-terminal current vs gate-voltage (R-DCIV or IB-VGB) and gate capacitance vs gate-voltage (CV or Cgb-VGB) properties of inversion n-channel Silicon MOS field-effect transistors. The shapes (called lineshapes) of the CV and IV curves are increasingly distorted as the interface trap concentration increases due to the VGB dependence of the trap-charge QIT from electrons trapped at the 1-electron neutral interface traps. The distortions are illustrated by four families of curves; each family covers a range of a device or trap parameter which is: interface trap concentration, basewell-body dopant impurity concentration, oxide thickness, or interface-trap energy level position in the Si energy gap. At high concentrations of interface traps, the low-frequency and high-frequency CV characteristics, distinguished by the trapping rate, Cgb-lf-VGB and Cgb-hf-VGB, show extreme distortions, with even two minima or one maximum in the CV valley.