Phase and Optical Characterizations of Annealed SnO Thin Films and Their p-Type TFT Application

Amorphous SnO thin films were prepared on quartz and 190 nm SiO(2)/Si(001) substrates by electron beam evaporation. X-ray diffraction results reveal that amorphous SnO transforms into polycrystalline alpha-SnO (tetragonal litharge structure) after rapid thermal annealing in Ar ambient at 350-400 degrees C and starts decomposing into o-SnO(2) (orthorhombic structure) with the expulsion of Sn atoms at 450-500 degrees C. The optical properties were characterized via spectroscopic ellipsometry. The polycrystalline SnO thin films have a higher refractive index n and a narrower bandgap E(g) than the amorphous ones, which is due to the polarizability enhancement in the crystallization process. Moreover, the relationship between n and Eg of the amorphous and polycrystalline SnO thin films can be explained by the Moss rule law, and a decreasing trend in n was verified with the transformation from SnO to SnO(2). Bottom-gate-type thin film transistors (TFTs) employing polycrystalline SnO channels on the SiO(2)/Si(001) substrates exhibit p-type field-effect transistor characteristics. The optimum field-effect mobilities mu(sat) and mu(lin) are 0.46 and 0.87 cm(2) V(-1) s(-1), respectively, which are the same order of magnitude as those reported for epitaxial SnO TFTs. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3385390] All rights reserved.