Miniband-width effects on Wannier–Stark localization of the first and second quantized states in a GaAs/AlAs superlattice

We performed electroreflectance (ER) measurements in order to reveal the transformation processes from the minibands to the Wannier–Stark (WS) localization states in a GaAs (6.8 nm)/AlAs (0.9 nm) superlattice. The high sensitivity of ER spectroscopy enabled us to observe the interband optical transitions associated with the second (n=2) minibands in addition to those associated with the first (n=1) minibands. It is found that the electric field strengths for the formation of the WS-localization states of the n=2 minibands are considerably higher than those of the n=1 minibands. The experimental results are quantitatively analyzed on the basis of the theoretical calculation of the electric-field-strength dependence of the miniband states using a transfer-matrix method. It is concluded that the critical electric field strengths for the formation of the WS-localization states clearly correlate with the miniband widths.