The electronic properties of amorphous and crystallized In2O3 films

Abstract

Polycrystalline In2O3 films with high crystallinity were prepared by annealing the amorphous In2O3 films deposited at room temperature by using dc/rf sputtering method. General electronic behaviors of both these amorphous and polycrystalline films have been investigated by means of Hall effect and resistivity measurements at temperatures between 4.2 and 300K. For the amorphous films, ionized impurity scattering dominates the electronic transport, and Hall mobility agrees well with the theory of degenerate semiconductors with divalent impurity scattering centers. On the other hand, the conduction mechanism of the polycrystalline films is governed dominantly by phonon scattering, since these films exhibit a clearly positive temperature coefficient of resistivity with the maximum Hall mobility of 150cm2∕Vs at 300K and 230cm2∕Vs at 4.2K, with little change in carrier concentration between these temperatures. Conductivity of both the amorphous and polycrystalline films is found to show a linear relationship in a double-logarithmic plot against carrier concentration between 4×1015 and 5×1020cm−3, a typical behavior of the impurity semiconductors with parabolic conduction band. For each set of films with the same thermal history, Hall mobility is found to vary on a convex upward curve with respect to carrier concentration. This behavior suggests a general and strong correlation of the structural defects introduced upon deposition and localization of conduction electrons with electron mobility, which led to a proposition of three categories for temperature coefficient of resistivity with major transport mechanisms of phonon scattering, divalent impurity scattering, and weak localization, respectively.