OBSERVATION OF WANNIER-STARK LOCALIZATION BY ELECTROREFLECTANCE SPECTROSCOPY

Wannier-Stark localization in strained-layer InxGa1-xAs-GaAs superlatt ices is measured using electroreflectance (ER) spectroscopy at 4.5 K. Analysis of the ER data reveals third-derivative line shapes for two s amples biased near flat band, which become more first-derivative-like at high applied fields. The exciton transition energies obtained from the line-shape analysis are in good agreement with both photocurrent m easurements and exciton Stark ladder calculations for fields greater t han 5 kV cm-1. The flat-band ER spectra of the two superlattices revea l distinct features due to their finite sizes, not predicted by the Kr onig-Penney model.