Space charged region in GaN and InN nanocolumns investigated by atomic force microscopy - Niebelschütz, M; Cimalla, V; Ambacher, O; Machleidt, T; Franke, KH; Ristic, J; Grandal, J; Sánchez-García, MA; Calleja, E (Physica Status Solidi (C) Current Topics In Solid State Physics, 2008)