The size dependence of tin oxide atomic cluster nanowire field effect transistors

Tin oxide (SnO(2)) cluster nanowires have been fabricated using atomic clusters as building blocks. Nanowires with widths of less than 100 nm were defined using electron beam lithography followed by deposition of Sn clusters which were subsequently thermally oxidized. The cluster nanowires were used to fabricate field effect transistors. The transistors were n-type and demonstrated a clear size-dependent behaviour. With zero gate bias the narrowest wires were depleted, both the carrier concentration and the conduction quickly increasing with wire width. This behaviour is attributed to the formation of a surface depletion region caused by Fermi level pinning. The width of the depletion region was estimated using the carrier concentration calculated from the transistor threshold voltages. The change in the wire conductance with UV illumination was also investigated. Illumination with 365 nm light increases the conduction by up to 40 times. This is attributed to a combination of an increase in carriers due to photo-desorption of oxygen from the surface of the wires and an increase in the mobility due to a reduction of inter-grain potential barrier height.