Light emission from nanoporous silicon and germanium quantum wires

Abstract

A model calculation has been carried out to investigate the room temperature luminescence intensity as a function of the size and the voltage of silicon (Si) and germanium (Ge) nanowires (NWs) having 10 to 40 atoms per wire with diameter ranging from 1.5 nm to 4.0 nm. The effects of exciton energy states, localized surface states and the quantum confinement are integrated in our phenomenological model to derive an analytical expression for the photoluminescence (PL) and electroluminescence (EL) intensity. It can explain very accurately the experimental PL and EL data and provide the mechanism for them. The model is quite general, applicable to quantum well and dots to study temperature dependent luminescence and current density. By controlling a set of fitting parameters in the model, one can tune the EL and PL peak and intensity. Our results show that both quantum confinement and surface passivation in addition to exciton effects determine the optical and electronic properties of Si and Ge NWs. We observed that the EL and PL intensities occurs at the same energy, however the EL intensity has sharp Gaussian sub peaks and red shifted compared to the PL intensity.