Photocurrent spectroscopy in a sawtooth doping superlattice

We report an investigation of photocurrent response in a sawtooth doping superlattice which is composed of alternating n(Si) and p(Be) δ-doping layers with undoped GaAs layers (7-15 nm) between them. A selective contact method is used to measure the interesting behavior of the subband gap compared with the gap of the host semiconductor. The photocurrent is finite even when the photon energy is below the gap of GaAs and can be varied by applying a bias voltage between the n and p contacts. The observed phenomena can be explained by a generalized Franz-Keldysh model which takes into account the finite voltage drop inside the sample.