Mechanism for the photovoltaic effect in heat-treated Cu 2SCdS heterojunctions

Abstract

A new rate equation formalism is proposed to analyze the gate oxide degradation of metal-oxide-semiconductor (MOS) capacitors under low fluence (⩽0.01 C/cm2) Fowler–Nordheim (FN) stress over a wide range of cathode electric field (6–12.5 MV/cm). Our present model is theoretically verified during constant current FN injection from the (100) n-Si substrate of n+-poly-Si-gate MOS capacitors with 22, 27 and 33 nm thick thermally grown SiO2 gate oxides. The present numerical simulation is based on the tunneling electron initiated trap-to-band ionization (TTBI) and band-to-band ionization (BTBI) as the possible coupled mechanisms for the generation of the trapped positive oxide charges near both interfaces of the samples studied here. Adopting the above coupled rate equation formalism, the trapping parameters are estimated utilizing the experimental data of FN voltage shift with injection time. The parameter values obtained from our present rigorous model differ in magnitude by ∽35–40% from those obtained by the traditional analysis based on either one of the above two mechanisms. The results obtained from the coupled dynamics are in good agreement with the experimental data of FN voltage shift as a function of electron fluence Qinj by Fazan et al. The present simulation gives an interesting feature that a steady-state plateau level in the FN voltage shift, Δ VFN, occurs at Qinj around 2×10−3 C/cm2 independent of oxide thickness and stress current density, consistent with earlier experimental observations.