Silicon-based light-emitting devices:: Properties and applications of crystalline, amorphous and Er-doped nanoclusters

In this paper, we summarize the results of an extensive investigation on the properties of MOS-type light-emitting devices based on silicon nanostructures. The performances of crystalline, amorphous, and Er-doped Si nanostructures are presented and compared. We show that all devices are extremely stable and robust, resulting in an intense room temperature electroluminescence (EL) at around 900 nm or at 1.54 mu m. Amorphous nanoclusters are more conductive than the crystalline counterpart. In contrast, nonradiative processes seem to be more efficient for amorphous clusters resulting in a lower quantum efficiency. Erbium doping results in the presence of an intense EL at 1.54 mu m with a concomitant disappearance of the 900-nm emission. This suggests that under electrical pumping Er is excited through an efficient energy transfer from the silicon clusters which hence become dark. We have identified an Auger de-excitation of Er with trapped carriers as the main process competing with radiative emission and limiting EL efficiency. This process is particularly severe in presence of unbalanced carrier injection (electrons versus holes) and can be controlled in properly designed structures. These data are presented and their implications are discussed.