Enhancing the efficiency of silicon based solar cells by confining photon and phonon in low dimensional structures -

Abstract

The interaction between phonons and photons, in ZnO NWs deposited on a silicon substrate and in silicon resonators arrays, is investigated by means of Raman spectroscopy. The Raman spectra from the ZnO NWs deposited on a silicon substrate exhibited a significant Raman enhancement from the Si substrate and did not show any signatures of Raman scattering from the ZnO nanowires. The analysis of this result demonstrated that the localized Mie resonance in the ZnO cylindrical resonators induced forward scattering of the normally incident light into the Si substrate beneath the resonators, on which the ZnO nanowires are deposited. On the other hand, the Raman spectra from large arrays of dielectric silicon resonators exhibited Raman enhancement accompanied with a downshift and broadening. The analysis of the Raman intensity and line shape using finite-difference time-domain simulations and a spatial correlation model demonstrated an interaction between photons confined in the resonators and phonons confined in nanosized crystallites in defective silicon in the resonators. It was shown that the Raman enhancement is due to collective lattice resonance inducing field confinement in the resonators, while the spectra downshift and broadening are signatures of the relaxation of the phonon wavevector due to phonon confinement in nanosized Si crystallites in the resonators. We found that as the resonators increase in height and their shape become cylindrical, the amplitude of their coherent oscillation increases and hence their ability to confine the incoming electric field increases.