Observation of Wannier-Stark ladders in multi-quantum well structures

When the strength of the electric field applied along the growth axis of a multi-quantum well is F approximate to 3 x 10(3) V cm(-1), we observe a series of peaks in the photocurrent (PC) spectrum. These peaks can be explained by the split of conduction states (minibands), which is due to interference of electrons above the barriers in the conduction band. More specifically, the peaks correspond to electron transitions from the ground state in a well to the conduction states above wells, including vertical transitions to the states above the well and the oblique transitions to the states above its neighbouring wells. The positions of the PC peaks in our experiments agree well with theoretical calculations.