Stark-ladder states in an imperfect crystal: Effect of impurity scattering

The effect of ionized impurity scattering on Stark-ladder states is theoretically studied. We derive an expression of a Stark-ladder state when the concomitant Bloch oscillation is interrupted by scattering. Based on a single band approximation, localized Stark-ladder states are expressed as a superposition of time-dependent Bloch functions through a path where an electronic state goes through. By means of the Monte Carlo method, we evaluate the localization length of Stark-ladder states in an infinite superlattice that contains impurity ions. We have found a power dependence of localization length on the electric field. Delocalization of a Stark-ladder state occurs giving rise to a decrease of the power. [S0163-1829(98)00944-8].