Temperature dependence of electrical properties of Ga-doped ZnO films deposited by ion plating with DC arc discharge

Abstract

Ga-doped ZnO (GZO) films with carrier concentration n ranging from 3×1018 to 1.04×1021cm−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 (μ)-temperature (T) curves (denoted by Δμ/ΔT) plotted as a function of n can be divided into three regions: (1) Region I (3×1018<n<4×1019cm−3); Δμ/ΔT>0 and μ decreasing with increasing n, (2) Region II (4×1019<n<3×1020cm−3); μ independent of T (Δμ/ΔT=0) and (3) Region III (n>3×1020cm−3); Δμ/ΔT<0. For all GZO films, the activation energies extracted from the 1000/T–ln (μT) curves were lower than the thermal energy kBT at 300K, 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 3×1018cm−3. The dependence of Δμ/ΔT 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.