Tin monoxide as an s-orbital-based p-type oxide semiconductor: Electronic structures and TFT application

Tin monoxide (SnO) is a stable p-type oxide semiconductor. This paper reports electrical properties, electronic structures, and thin-film. transistors (TFTs) of SnO. Epitaxial films were fabricated by pulsed laser deposition. The Hall mobility and the hole density of the epitaxial films were 2.4 cm(2) V(-1) s(-1) and 2.5 x 10(17), respectively. X-ray photoelectron spectroscopy (PES) indicated that the closed-shell 5s(2) orbitals of Sn(2+) ions heavily contribute to the hole conduction path in SnO. Top gate type TFTs (W/L = 300/50 mu m) employing 20 nm thick SnO channels exhibited field-effect mobilities mu(sat) = 0.7 cm(2) V(-1) s(-1) and mu(lin) = 1.3 cm(2) V(-1) s(-1), which are larger by two orders of magnitude than those reported for p-channel oxide TFTs to date. On/off current ratios were similar to 10(2) and subthreshold voltage swings (S) similar to 7 V/decade. The parameters required for TFT simulations were estimated by ultraviolet PES and first-principles calculations. The TFT simulations indicated that subgap hole trap density in the SnO channel is > 10(19) cm-3, which limits the TFT mobilities and the S values. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim