P-type conductivity in hydrogenated radio frequency sputtered tin oxide thin films

P-type oxide semiconductors are being intensively investigated for their potential use in optoelectronic and microelectronic applications, such as active electronics and transparent transistors. In this work, the p-type conductivity of tin oxide thin films was examined. The films were deposited using radio frequency magnetron sputtering in an atmosphere containing a mixture of hydrogen and argon. The structural, chemical, optical, and electrical properties of the films were analyzed as the hydrogen-to-argon concentration was varied from 0% to 20%. The films were polycrystalline except those deposited under the highest hydrogen concentration which became amorphous. Chemical analysis of the films revealed a substantial concentration of oxygen vacancies. Optically, the films were transparent and their band gaps decreased as the hydrogen concentration increased. The pure tin oxide films had n-type conductivity, which was attributed to oxygen vacancies. However, the conductivity was converted to p-type as the hydrogen concentration increased. This was attributed to the formation of hydrogen shallow acceptor states, which was supported by the observation of a red-shift of the band gap. The optimum hydrogen concentration for p-type conductivity was found to be 10%. The p-type character of the films was demonstrated by fabricating a hetero p-n junction based on SnO2/Si, which exhibited the expected non-linear diode rectification behavior.