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We study the localization/delocalization property of disordered $GaAs?AI_{x}Ga_{1-x}As$ semiconductor
superlattices with structural short-range correlations(so-called random-dimer model).Our system
consists of square quantum barriers and wells with the same thickness and the heights of barriers have
two different values.Using transfer matrix method,we calculate localization length of the system and
show that there are two different delocalized states in the system.The energy of these extended states
depends on the fraction of Al in the barriers.Then,we consider the divergence of the localization length
near the extended state.
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