Research of carrier mobility in NPD through negative differential susceptance spectra Hui Xu, Chao Tang, Wen-Juan Zhai, Rui-Lan Liu, Zhou Rong, Qu-Li Fan and Wei Huang Eur. Phys. J. Appl. Phys., 68 3 (2014) 30202 Published online: 12 December 2014 DOI: 10.1051/epjap/2014140298