Origin of carrier scattering in polycrystalline Al-doped ZnO films

We observed the carrier transport phenomena in polycrystalline Al-doped ZnO (AZO) films with carrier densities ranging from 2.0 x 10(19) to 1.1 x 10(21) cm(-3). A comparison of the optical carrier density and Hall carrier density indicates that the conduction band in AZO films is nonparabolic above 2.0 x 10(20) cm(-3). A transition from grain boundary scattering to ionized impurity scattering is observed at a doping level of x 10(20) cm(-3). The trap density at the grain boundary increases with increasing Al concentration in the films, implying that the doping level plays a decisive role in the trap density. The excellent fitting of the optical mobility and carrier density using the Brooks-Herring model shows that the acceptor concentration increases with increasing doping level. (C) 2014 The Japan Society of Applied Physics