Ga-doped ZnO (GZO) films with carrier concentration n ranging from 3 x 10(18) to 1.04 x 10(21) cm(-3) were deposited by ion plating with DC arc discharge. The results of Hall effect measurements of the GZO films revealed that the gradients of Hall mobility (mu)-temperature (T) curves (denoted by Delta mu/Delta T) plotted as a function of n can be divided into three regions: (1) Region I (3 x 10(18) < n < 4 x 10(19) cm(-3)); Delta mu/Delta T > 0 and mu decreasing with increasing n, (2) Region II (4 x 10(19) < n < 3 x 10(20) cm(-3)); mu independent of T (Delta mu/Delta T = 0) and (3) Region III (n > 3 x 10(20) cm(-3)); Delta mu/Delta T<0. For all GZO films, the activation energies extracted from the 1000/T-ln (mu T) curves were lower than the thermal energy k(B)T at 300 K, indicating that the carrier electrons can overcome the potential barriers at grain boundaries. Moreover, comparison of the calculated mean free path l of the carrier electrons and the depletion layer width at the grain boundaries showed that the grain boundary scattering mechanism plays a minor role in the carrier transport compared with the intra-grain scattering mechanism for GZO films with n higher than 3 x 10(18) cm(-3). The dependence of Delta mu/Delta T on n demonstrates the continuous transformation of the dominant intra-grain scattering mechanism from the ionized impurity scattering mechanism to the phonon scattering mechanism with increasing n. (c) 2012 Elsevier B.V. All rights reserved.