Analysis of the feedback voltage during constant current avalanche hole injection experiments

Abstract

The behavior of the controlling feedback voltage during constant current avalanche hole injection experiments on metal-oxide-semiconductor capacitors has been analyzed in detail. It is concluded that at dc hole current densities greater than 50 nA/cm2, displacement currents generated in the oxide as a result of a change in the feedback voltage can dominate the injected hole current. The effect of this displacement current on the determination of hole trapping kinetics is evaluated quantitatively. In particular, it is shown that the effect of the displacement current is to reduce the hole current density and cause an apparent delay in oxide charging kinetics. In addition, it is shown that the feedback voltage necessary to maintain current densities larger than 50 nA/cm2 induces a measurable electron current from the gate electrode when the oxide field exceeds 6 MV/cm. Analysis of this phenomenon provides evidence for hole trapping at the Al-SiO2 interface as well as an estimate of the capture cross section for this process. The estimated cross section,1×10−14 cm2, is similar in magnitude to that obtained for hole trapping at the Si-SiO2 interface. It is concluded that while displacement currents and gate electron injection may affect the determination of hole trapping kinetics, these effects can be avoided at current densities below 50 nA/cm2. Finally, consideration of the relative changes in the feedback and flat-band voltage data during low-current density experiments suggests that the feedback voltage does not respond to charge in interface traps.