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Abstract: CuxS thin films, 80nm thick, are deposited by vacuum thermal evaporation of sulfur-rich powder mixture, Cu2S:S (50:50wt.%) with no intentional heating of the substrate. The process of deposition occurs at very low deposition rates (0.1–0.3nm/s) to avoid the formation of Cu or S-rich films. The evolution of CuxS films surface properties (morphology/roughness) under post deposition mild annealing in air at 270°C and their integration in a thin film transistor (TFT) are the main objectives of this study. Accordingly, Scanning Electron Microscopy studies show CuxS films with different surface morphologies, depending on the post deposition annealing conditions. For the shortest annealing time, the CuxS films look to be constructed of grains with large dimension at the surface (approximately 100nm) and consequently, irregular shape. For the longest annealing time, films with a fine-grained surface are found, with some randomly distributed large particles bound to this fine-grained surface. Atomic Force Microscopy results indicate an increase of the root-mean-square roughness of CuxS surface with annealing time, from 13.6 up to 37.4nm, for 255 and 345s, respectively. The preliminary integration of CuxS films in a TFT bottom-gate type structure allowed the study of the feasibility and compatibility of this material with the remaining stages of a TFT fabrication as well as the determination of the p-type characteristic of the CuxS material. [Copyright &y& Elsevier]

Abstract: The influence of tin doping on the electrical, optical, structural and morphological properties of indium oxide films produced by radio-frequency plasma enhanced reactive thermal evaporation is studied, as transport properties are expected to improve with doping. Undoped and tin doped indium oxide thin films are deposited at room temperature using both pure In rods and (95–80) % In:(5–20) % Sn alloys as evaporation sources and 19.5mW/cm2 and 58.6mW/cm2 as rf-power densities. The two most important macroscopic properties – visible transparency and electrical resistivity – are relatively independent of tin content (0–20%). Visible transmittance of about 75% and electrical resistivity around 5×10−4 Ω·cm can be observed in the films. The structural features are similar for all samples. Nevertheless, the surface morphology characterization shows that the homogeneity of the films varies according to the tin content. Moreover this variation is a balance between the rf-power and the tin content in the alloy: i) films with small and compact grains are produced at 58.6mW/cm2 from a 5% Sn alloy or at 19.5mW/cm2 from a 15% Sn alloy and consequently, smooth surfaces with reduced roughness and similar grain size and shape are obtained; ii) films showing the presence of aggregates randomly distributed above a tissue formed of thinner grains and higher roughness are produced at the other deposition conditions. [Copyright &y& Elsevier]

Abstract: TiO2 films with enhanced photosensitivity were deposited on alkali free glass substrates without intentional substrate heating by pulsed DC magnetron reactive sputtering with an average thickness of about 2μm. Three dyes, commercial N719 and two new organic dyes were impregnated in order to control the optical spectral selectivity of such films. The type of dye used proved to dramatically influence the device''s response to radiation pulses. The practical breakthrough is the use of different dyes according to the region of the electromagnetic spectrum one wants to detect. Devices with photocurrent 6 orders of magnitude higher than the dark current (from ∼2×10−12 to 2×10−6 A for a 100V bias) were fabricated with a spectral response within the visible range of the electromagnetic spectrum. In addition, this approach is likely to allow for the fabrication of hybrid photodetectors on cheap heat sensible flexible polymeric substrates. [Copyright &y& Elsevier]

Abstract: Transparent, undoped semiconductive thin films of zinc oxide were deposited by radio frequency plasma enhanced reactive thermal evaporation of zinc rods in the presence of oxygen at room temperature, without any post-deposition annealing treatments. The study of the variation of rf power, in the range 5–200W, on the main properties of these films was made. A decrease of the electrical conductivity of these films with increasing rf power was observed (10−3 to 10−12 (Ωcm)−1), respectively, while the average visible transparency was kept practically constant (≈80%). From this initial study, a set of bottom-gate type thin-film transistors were made using the most promising semiconductor materials. Preliminary I(V) measurements showed all transistors working, with best results obtained from zinc oxide material deposited at the lowest rf power (20W), within the deposition conditions range which leads to semiconductive material. Such devices presented an I on (20V)/I off (−5V) ratio of 6×106 and a field-effect mobility of 0.37cm2/(Vs). [Copyright &y& Elsevier]

Copper oxide is a well known p-type semiconductor material, usually obtained by thermal oxidation of copper thin-films within few minutes, at atmospheric pressure. In this paper, thin films of copper oxide that were deposited by radio-frequency plasma enhanced reactive thermal evaporation of copper at room temperature, without any post-deposition annealing treatment, are studied. The deposition of good quality p-type semiconductor oxide to be used in the fabrication of p-TFTs is the purpose of this work. The thickness of the films varies from 97 up to 160 nm. The influence of rf power density on chemical, electrical and optical properties of the films was studied. Samples present conductivity within the range of 6 x 10(-5) to 4 x 10(2) omega(-1) x cm(-1) (thermal activation energy in the interval 0.46 to 0.01 eV). The p-type conductivity of the films was confirmed by Seebeck effect in the more conductive samples. Surface composition obtained by XPS analysis was correlated with optical and electrical properties, showing that rf-power plays a main role in changes of material characteristics.

Conductive and transparent undoped thin films of indium oxide (InOx ), 120 nm average thick, were deposited by radio frequency plasma enhanced reactive thermal evaporation (rf-PERTE) of indium in the presence of oxygen at room temperature. Several substrates were used in order to study their influence on the main properties of these films: alkali free (AF) glass, fused silica, crystalline silicon and polyethylene terephthalate (PET). Surface morphology of the InOx films as a function of the substrates was observed by SEM and showed that the undoped InOx films obtained are nanostructured. For the c-Si substrate, InOx films with increased grain size are obtained, induced by the crystalline substrate. Films deposited on fused silica and AF glass substrates show a nano-grainy surface with similar surface morphologies. The InOx films deposited on AF glass show the highest values of both: electrical conductivity of about 1100 (omega cm)(-1) and visible transmittance of 85%. The substrate has a greater influence on the surface morphology of the films when a polymer (PET) is used. InOx films deposited on PET show a decrease in the electrical conductivity (90 (omega cm)(-1)) and a slight decrease in the average visible transmittance (78%).

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 radiofrequency 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 x 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.