Franz-Keldysh effect in the interband optical absorption of semiconducting nanostructures

We present a theoretical calculation of the effect of an electric field applied either parallel or perpendicular to the direction of confinement on the interband optical absorption of semiconducting nanostructures such as quantum wells, quantum wires, and quantum boxes. We find that the application of the electric field decreases the optical absorption coefficient for both the parallel and perpendicular to the direction of carrier confinement. The absorption is greater when the electric field is along the direction of carrier confinement than when it is perpendicular to the direction of carrier confinement. Our work differs from that of others in that we present detailed theoretical calculations of the effect of the electric field on the optical absorption coefficient and obtain analytical expressions for the absorption coefficient. We find that there are additional oscillations in the absorption above the effective band gap in addition to the structure in the absence of the electric field, which are due to the Franz-Keldysh effect for the electric field parallel to the axis of the wire and the plane of the well. Numerical results also show that there is a smaller threshold for the optical absorption of cylindrical wires than for rectangular wires with the same cross sectional area.