Optical properties of silicon nanocrystal LEDs

In this work, we describe how to fabricate good quality <f>3 nm</f> nc-Si with low size distribution in thermal <f>SiO2</f> 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–Schro¨dinger 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 <f>3 nm</f> dots which show a threshold energy around <f>2 eV</f>. However, the optical recombinations seems to be related to lower energy states probably due to interfacial radiative defects around <f>1.58 eV</f>. 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 <f>I</f>–<f>V</f> measurements confirm that the current is related to a pure tunnelling process. A modelling of <f>I</f>–<f>V</f> curves confirms a Hopping mechanism with an average trap distance between 1.4 and <f>1.9 nm</f>. The Fowler–Nordheim process is not observed during light emission for electric fields below <f>5 MV/cm</f>. Finally, we have not hot carrier injection and thus it seems possible to develop Si-based LEDs with a good reliability. [Copyright &y& Elsevier]