Effects of carrier storage in an uncapped Ge–Si core–shell nanocrystal on simulated nano-electron beam induced current

Abstract

Carrier trapping process inside an uncapped and spherical Ge–Si core–shell nanocrystal on the surface of an n-doped Si substrate and its effects on electron beam induced current are studied using a three-dimensional Monte Carlo simulation. Charges are generated using an electron beam energy of 5 keV in the perpendicular configuration and collected by a nanoscale electrode which establishes a nanojunction with the Si sample. The surface recombination velocity is equal to zero. The Ge–Si core–shell is assumed to exhibit type II confinement of band edge alignment in which holes are trapped inside the core and electrons inside the shell. The collection and trapping probabilities of a created carrier, when it emerges at the sample surface, are controlled by its electric nature (hole or electron), by distances separating it from the core–shell nanocrystal and from the nanoelectrode. Carrier probabilities and collection are also controlled by opening angles allowing the emerged charge to “see” the core–shell nanocrystal and the nanoelectrode. Results show that the electron trapping is distance independent, and it does not affect the induced current, while the hole collection and trapping processes depend on each other up to a threshold distance of ∼200 nm. Beyond this distance, no modification is observed either in the induced current, suggesting that the nanocrystal can no longer be detected, or in the hole capture process, suggesting a no potential overlapping between the nanocrystal and the nanoelectrode.