Intersubband absorption in Si/Si1−x−yGexCy quantum wells

Abstract

Intersubband absorption in the valence band of Si–Si1−x−yGexCy multiquantum wells is reported. The quantum wells with x≊17% and y≊1% and thicknesses around 3 nm are grown pseudomorphically by rapid thermal chemical vapor deposition on Si(001). The carbon is incorporated in substitutional site using methylsilane as the gas precursor. The quantum wells exhibit near-band-edge photoluminescence with no-phonon and phonon-assisted replica. The energy position of the no-phonon and phonon-assisted replica are shifted to high energy with respect to bulk alloys due to the quantum confinement of the first heavy hole subband. The intersubband absorption between confined subbands is measured in a multipass waveguide geometry under optical pumping. Absorptions for light with an electric field polarized either parallel or perpendicular to the growth axis are observed in both SiGe and SiGeC quantum wells. The absorptions peak at 100 and 130 meV and involve bound-to-bound and bound-to-continuum transitions. The spectral positions of the intersubband absorptions are discussed from numerical calculations accounting for the band gap variation induced by carbon.