Oscillator-strength modification of Stark ladder transitions due to resonance-induced wavefunction delocalization in a GaAs/AlAs superlattice under the electric field

Spatially direct and indirect Stark ladder optical transitions and their electric-field-induced evolution have been investigated in a GaAs/AlAs (L-Z = 6.4 nm/L-B = 0.9 nm) superlattice by low-temperature photocurrent spectroscopy. When the ground and first excited electron Stark ladder states resonate between the nearest-neighbor wells, it is found that oscillator strengths of the direct (n = 0) and indirect (n = +1) Stark ladder transitions are strongly modified, accompanying enhanced anticrossings. The observed modification effects on the oscillator strength of the transitions are rigorously explained in terms of the wave function delocalization after the complete Wannier-Stark localization due to the resonant couplings between the adjacent wells, based on transfer matrix calculations of the ladder eigenstate and the wave function overlap integrals between the electron and hole subband states. (C) 2001 Elsevier Science B.V. All rights reserved.