Single-crystalline zinc oxide nanowires with diameters of 90 to 200nm were

synthesized by using the thermal evaporation method. Four-probe Ti/Au electrodes

were made by using the standard electron-beam lithography technique, and the

intrinsic resistivities, ρ(T), of individual nanowires were measured from 300 to

0.25K. The temperature behaviour of ρ(T) between 300 and 5K revealed that the

intrinsic electrical-transport mechanisms through individual ZnO nanowires were

due to a combination of thermal activation conduction and nearest-neighbour

hopping conduction processes. Three distinct activation and hopping contributions,

with discrete characteristic activation energies, were observed. Above about 100K,

the charge transport mechanism was dominated by the thermal activation of

electrons from the Fermi level, μ, into the conduction band. Between about 20 and

100K, the charge transport mechanism was due to activation of electrons from μ to

the upper impurity (D−) band. Between about 5 and 20K, the charge transport

mechanism arose from nearest-neighbour hopping conduction within the lower

impurity (D) band. Such unique behaviours could be explained in terms of the

intricate material properties (in particular, the presence of moderately high

concentrations of n-type defects accompanied by slight self-compensation) in

natively-doped ZnO nanowires. In one heavily-doped nanowire, a surface-related

conduction process exhibiting the two-dimensional attributes of quantuminterference

transport phenomena was observed. The carrier concentrations in the

nanowires were deduced to lie close to the critical concentration for the Mott

metal–insulator transition.

Electrical Conduction Mechanisms in Natively Doped ZnO Nanowires. S.P.Chiu,

Y.H.Lin, J.J.Lin: Nanotechnology, 2009, 20[1], 015203