First-principles study of the electronic and optical properties of Si with nanometer-sized pores

Abstract

Electronic and optical properties of crystalline (np-cSi) and amorphous Si (np-aSi) containing periodically arranged nanometer-sized pores are investigated through first-principles density functional theory calculations. It is demonstrated that the quantum confinement, which is responsible for the increase of the energy gap, has a stronger effect for np-cSi due to the structural regularity. The computed imaginary part of the dielectric function (epsilon(2)(omega)) decreases as a function of pore size due to the volume effect, but the confinement effect shifts the peak position of epsilon(2)(omega) to a higher energy. This blue-shift is not reproduced within effective medium theory, which implies that the electronic structure needs to be properly taken into account for correct description of optical properties in porous Si geometry.