Electroluminescence of silicon nanocrystals in MOS structures

We have studied the structural, electrical and optical properties of MOS de vices, where the dielectric layer consists of a substoichiometric SiOx (x < 2) thin film deposited by plasma-enhanced chemical vapor deposition. After deposition the samples were annealed at high temperature (> 1000 degreesC) to induce the separation of the Si and the SiO2 phases with the formation of Si nanocrystals embedded in the insulating matrix. We observed at room t emperature a quite intense electroluminescence (EL) signal with a peak at s imilar to 850 nm. The EL peak position is very similar to that observed in photoluminescence in the very same device, demonstrating that the observed EL is due to electron-hole recombination in the Si nanocrystals and not to defects. The effects of the Si concentration in the SiOx layer and of the a nnealing temperature on the electrical and optical properties of these devi ces are also reported and discussed. In particular, it is shown that by inc reasing the Si content in the SiOx layer the operating voltage of the devic e decreases and the total efficiency of emission increases. These data are reported and their implications discussed.