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\bibitem{Helm_etal1992} {\textquotedblleft}\textit{Infrared spectroscopy of subbands, minibands, and donors in GaAs/AlGaAs superlatices}{\textquotedblright}. Helm M, Peeters FM, DeRosa F, Colas E, Harbison JP, Florez LT, Surface science \textbf{263}, 518 (1992)

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