Polarized Raman and photoluminescence study on silicon quantum wires

Abstract

A detailed Raman and photoluminescence study was performed on Si quantum wires fabricated on crystalline silicon (100). A shift of the phonon frequency was observed indicative of a compressive stress of about 9.5 kbar, possibly originating from the oxide skin grown on the wire surface by high temperature thermal oxidation. A splitting of the Raman phonon was also observed and interpreted as originating from the existing stress and/or from the excitation of phonons polarized parallel and normal to the direction of confinement. The photoluminescence emission was found to depend on the excitation wavelength and on the polarization of the laser beam. The energy and efficiency of the emitted luminescence increased with decreasing laser wavelength. This was interpreted as an effect due to the size distribution of the studied wires, since thin wires with a higher band gap than thick wires can be excited by shorter laser wavelengths. The photoluminescence efficiency was significantly higher when the laser beam was polarized in the direction of confinement in agreement with theoretical predictions. The emitted luminescence was also polarized preferentially in the direction of confinement. This resulted in depolarization of the emitted light when the laser beam was polarized along the wire axis, normal to the direction of confinement.