Traps in germanium nanocrystal memory and effect on charge retention: Modeling and experimental measurements

Abstract

Surface traps, or traps at the interface of the nanocrystal and the surrounding matrix, play an important role in the charge retention performance of nanocrystal memory transistors. In this article, we report the investigation of trap energy levels in nanocrystalline germanium (nc-Ge) memory transistor and capacitor structures and their effect on the device charging and discharging kinetics through theoretical modeling and experimental measurements. The theoretical model, calibrated using the experimental data, uses a self-consistent quantum-mechanical tunneling numerical approach for calculating the transmission coefficient across the tunnel barrier. The effect of the trap energy on charge retention is shown by temperature-dependent measurements on the nc-Ge memory structures. The trap energy-level requirement for achieving a specified long-term charge retention performance (i.e., 10-yr retention time) is obtained from simulation as a function of the nanocrystal size.