Metal-semiconductor transition and negative magneto-resistance in degenerate ultrathin tin oxide films

A study of electron- and magneto-transport behavior of ultrathin SnO2 films of thickness ≤40 nm with high conductivity of 537 Ω−1 cm−1 deposited on glass substrate by using DC reactive sputtering has been carried out at low temperature. Hall effect measurements revealed these SnO2 films to be degenerate down to 40 K. The films with thickness >5 nm are found to undergo a metal-semiconductor transition below 140 K, and show a negative MR of ∼1.5% at a magnetic field of 0.9 T below 40 K. Both these phenomena have been ascribed to the presence of weak localization of electrons at low temperature. Electron transport behavior has been explained using quantum correction to conductivity. Estimated inelastic scattering lengths were found to be longer than the film thickness which supports two-dimensional nature of electron- and magneto-transport in these ultrathin films.