Optical properties of silicon nanocrystal LEDs

In this work, we describe how to fabricate good quality View the MathML source nc-Si with low size distribution in thermal SiO2 oxides. Photoluminescence, excited photoluminescence, and photocurrent measurements are discussed on the basis of theoretical calculations of the quantified levels in nc-Si. The impact of shape and size in quantum dots on transition energies has been highlighted, thanks to 2D symmetrical self-consistent Poisson–Schrödinger simulations. Both direct and indirect gaps in silicon have been considered in order to carry out a better comparison between simulations and optical measurements. A good agreement is found between simulations and experimental data for the indirect gap of View the MathML source dots which show a threshold energy around View the MathML source. However, the optical recombinations seems to be related to lower energy states probably due to interfacial radiative defects around View the MathML source. On the basis of highly luminescent nc-Si, we have fabricated an optimized light emitting device (LED) with a calculated design in order to favour both electron and hole injection. Stable red electroluminescence has been obtained at room temperature and the I–V measurements confirm that the current is related to a pure tunnelling process. A modelling of I–V curves confirms a Hopping mechanism with an average trap distance between 1.4 and View the MathML source. The Fowler–Nordheim process is not observed during light emission for electric fields below View the MathML source. Finally, we have not hot carrier injection and thus it seems possible to develop Si-based LEDs with a good reliability.