Calculated PL lifetimes of Si nanowires: the effect of a dispersion in the crystallographic orientations

The photoluminescence (PL) lifetimes have been calculated within effective mass approximation for Si nanowires with a rectangular cross section as a function of their size and their crystallographic direction. Both direct and indirect transitions are found. More than one subband can contribute to the PL lifetime. Depending on the crystallographic direction of the wires, the calculated lifetimes range between microseconds to milliseconds at room temperature. The distribution of the magnitudes of the PL lifetimes assuming a Gaussian distribution for the crystallographic orientations of the quantum wires is discussed.