Electric field effects on reduced effective masses of minibands at the mini-Brillouin-zone center and edge in a GaAs/AlAs superlattice.

We have investigated the electric-field-strength dependence of the reduced effective masses of the minibands in a GaAs/AlAs superlattice embedded in a p-i-n diode structure with use of electroreflectance spectroscopy. Frantz-Keldysh (FK) oscillations are observed in the energy region between the n = 1 heavy hole to electron transition at the mini-Brillouin-zone center (kz = 0: Γ point) and that at the edge (kz = π/D: π point), where D is the superlattice period. Analyzing the FK oscillations, we evaluate the reduced effective masses at the Γ and π points as a function of electric field strength. The evaluated reduced effective masses are consistent with the values estimated from the calculated miniband dispersion relations in a low electric field regime. It is found that the reduced effective masses tend to be heavier at a given electric field strength. Considering the electric-field-strength dependence of eigenstates calculated using a transfer-matrix method, we conclude that an increase of the reduced effective masses originates from weak localization of the electron envelope function in the transformation process from the miniband to Stark-ladder states in Wannier-Stark localization. [ABSTRACT FROM AUTHOR]