Photoconductivity as a method to probe defects in ultra thin Si films

Abstract

Silicon-on-insulator wafers with thicknesses of a boron doped p-type device layer 1.5 μm to 88 nm are probed by means of photoconductive spectroscopy. It is shown that the boron acceptor manifests itself as Fano resonances at 669 and 693 cm–1 associated with the excited states due to the spin-orbit split-off valence band as well as Γ-phonon replicas of intrinsic boron transitions associated with the states of the top of the valence band. More importantly, electrically neutral oxygen-related defects including interstitial oxygen also appear in the photoconductivity spectra as dips at the frequencies of the corresponding local vibrational modes. These findings demonstrate selectivity and high sensitivity of photoconductive spectroscopy, which make it a preferential technique to probe semiconductor thin films.