P -type conduction mechanism in continuously varied non-stoichimetric SnO_x thin films deposited by reactive sputtering with the impedance control

We successfully fabricated a series of SnO x films varying from SnO 2 to SnO using reactive sputtering. By precisely tailoring the transition region in reactive sputtering, a continuous structural evolution from SnO 2 to SnO was observed with SnO 2 films showing a typical columnar structure and SnO films having a dense film structure with larger crystallites. X-ray diffraction measurement confirmed that the fabricated SnO films coexist with the minor SnO 2 and Sn 3 O 4 phases. SnO films exhibit an unintentional p-type conductivity, and the interstitial oxygen possibly acts as the acceptor. The maximum hole mobility is 3.38 cm 2 / V s at a hole concentration of 1.12 × 10 18 cm - 3. We propose a p-type conduction mechanism for those SnO x films with the major SnO phase coexisting with the minor SnO 2 and Sn 3 O 4 phases, in which the possible optimum for the hole transport can be achieved by tailoring the balance between the amounts of the SnO 2 / Sn 3 O 4 phases and interstitial oxygen.