WAVE-FUNCTION DELOCALIZATION OF STRONGLY-LOCALIZED STARK-LADDER STATES IN A GAAS ALAS SUPERLATTICE/

We have investigated the wavefunction-localization properties as a fun ction of electric field from similar to 30 to similar to 300 kV/cm in a GaAs(6.8 nm)/AlAs(0.8 nm) superlattice by using electroreflectance s pectroscopy to observe Stark-ladder transitions. It has been found fro m the electric-field dependence of the electroreflectance spectra that the electron wavefunctions are delocalized after they are fully local ized in individual quantum wells in a high electric-field regime. We c onclude that the wavefunction delocalization results from the tunnelin g effect induced by the interaction between the spatially-separated fi rst and second Stark-ladder states from the analysis of the eigenstate s based on a transfer-matrix method in the framework of an envelope-fu nction approximation. (C) 1998 Elsevier Science Ltd. All rights reserv ed.