Modeling direct modulation dynamics in silicon nanocrystal light emitting transistors

We investigate the physical mechanisms that compromise the modulation speed of electroluminescence (EL) from silicon nanocrystals (Si-nc) embedded in the gate oxide of field effect transistors. A rate equation that explicitly includes an Auger term proportional to the charge density in the silicon nanocrystal layer is used to study the observed modulation. It is found that the main frequency limitation arises from the luminescence rise time. A comparison between simulation and experiment shows that the reported value of the absorption cross-section of electrically excited Si-nc (sigma_Si=10^-14 cm²) is strongly dependent on the particular device implementation. We find that an ideal silicon nanocrystal embedded in a defect-free SiO₂ must have an intrinsic absorption cross-section of ~ sigma_Si=10^-12 cm² which means that there is a wide margin for electrical injection optimization.