Electronic states and optical properties of silicon nanocrystals

Photoluminescence properties of nanometer Si-based materials have motivated a great deal of experimental and theoretical research effort because they exhibit favourable applications in opto-electronic devices. The quantum confinement effect of photoexcited carriers within nanocrystallites was mainly proposed to be responsible for the visible luminescence from these materials. In this work, the electronic states and optical transition properties of Si nanocrystals are studied by means of an sp3s* semiempirical tight-binding approximation and supercell model, in which the silicon nanocrystals are columns of square cross-section with width from a to 7a, where a is the lattice constant. The calculations have been carried out for light polarized in the [1 0 0] direction, i.e., perpendicular to the wire alignment. We present the dependence of the imaginary part of the dielectric function on the quantum confinement within two different schemes, which are applied and compared.