Effects of quantum states on the photocurrent in a "superlattice"

Photocurrent measurements in GaAs-GaA1As superlattices grown by molecular-beam epitaxy enable us to observe simultaneously quantum states and associated anomalous conductance. The spectrum in the photocurrent shows a series of peaks of photon energies corresponding to transitions between quantum states in the valence and conduction bands. As a function of applied voltage, the photocurrent exhibits pronounced negative differential conductance when the potential-energy difference between two adjacent wells of the superlattice exceeds the bandwidth of the quantum states. © 1975 The American Physical Society.