Orientation-dependent charge carrier confinement in a nanopatterned silicon film

From first-principles calculations, we find that in a (110) Si film with surface etching along the [001] direction, the holes can be confined underneath the patterned layer. This effect arises from the interplay between the anisotropic carriers and the patterning-induced quantum confinement. An anisotropy coefficient K= m_z / m_y, which is the ratio between the out-of-plane effective mass and the in-plane effective mass of the charge carriers in the film, is introduced to explain the orientation dependence. We propose that a modulation-dopinglike effect can be achieved in the (110) nanopatterned Si film by selective doping in the top patterned layer.