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\bibitem{Shields_etal2001} {\textquotedblleft}\textit{Free-carrier effects in gallium nitride epilayers: Valence-band dispersion}{\textquotedblright}. Shields PA, Nicholas RJ, Peeters FM, Beaumont B, Gibart P, Physical Review B \textbf{64}, 155303 (2001).   http://doi.org/10.1103/PhysRevB.64.081203

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