Relationship between variable range hopping transport and carrier density of amorphous In2O3–10 wt. % ZnO thin films

Abstract

The electrical transport characteristics in amorphous Zn doped In2O3 films have been investigated in the range from 2 × 1017 cm−3 to 6 × 1020 cm−3 of the carrier concentration Ne. For films with Ne > 3 × 1020 cm−3, it is found that the Hall mobility μH is limited by ionized impurity scattering. However, for films with Ne < 1 × 1020 cm−3, the Ne dependence of μH is given by the relation of μH ∝ Ne1/3. The temperature T dependence of resistivity ρ(T) changes from exhibiting metallic behavior with dρ/dT > 0 to insulating behavior with dρ/dT < 0 near Ne≈1 × 1020 cm−3 with decreasing Ne. The transport mechanism of carriers in the high-resistivity region is discussed by considering a model based on the Ioffe-Regel criterion. For the film with highest resistivity with Ne ≈ (5 − 6) × 1017 cm−3 among the present films, the ρ(T) show a change from Mott variable-range hopping (ρ ∝ exp T−1/4) to ρ ∝ expT−1/2 at approximately 10 K with decreasing temperature.