Guilherme Lavareda

In view of the increasing need for larger-area display devices with improved image quality it becomes increasingly important to decrease resistivity while maintaining transparency in transparent conducting oxides (TCOs). Accomplishing the goal of increased conductivity and transparency will require a deeper understanding of the relationships between the structure and the electro-optical properties of these materials. In this work we study the role of tin doping in InOx thin films. Undoped indium oxide (InOx) and indium tin oxide (ITO) thin films were deposited at room temperature by radio-frequency plasma enhanced reactive thermal evaporation (rf-PERTE), a new technique recently developed in our laboratory using as evaporation source either In rods or a 90%In:10%Sn alloy, respectively. The two most important macroscopic properties-optical transparency and electrical resistivity-seem to be independent of the tin content in these deposition conditions. Results show that the films present a visible transmittance of the order of 82%, and an electrical resistivity of about 8 x 10(-4) Omega . cm. Surface morphology characterization made by atomic force microscopy (AFM) showed that homogeneity of the films deposited from a 90%In:10%Sn alloy is enhanced (a film with small and compact grains is produced) and consequently a smooth surface with reduced roughness and with similar grain size and shape is obtained. Films deposited from pure In rods evaporation source show the presence of aggregates randomly distributed above a film tissue formed of thinner grains.

Nowadays, among the available transparent semiconductors for device use, the great majority (if not all) have n-type conductivity. The fabrication of a transparent p-type semiconductor with good optoelectronic properties (comparable to those of n-type: InOx, ITO, ZnOx or FTO) would significantly broaden the application field of thin films. However, until now no material has yet presented all the required properties. Cu2S is a p-type narrow-band-gap material with an average optical transmittance of about 60% in the visible range for 50 nm thick films. However, due to its high conductivity at room temperature, 10 nm in thickness seems to be appropriate for device use. Cu2S thin films with 10 nm in thickness have an optical visible transmittance of about 85% rendering them as very good candidates for transparent p-type semiconductors. In this work CuxS thin films were deposited on alkali-free (AF) glass by thermal evaporation. The objective was not only the determination of its optoelectronic properties but also the feasibility of an active layer in a p-type thin film transistor. In our CuxS thin films, p-type high conductivity with a total visible transmittance of about 50% have been achieved. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim