Guilherme Lavareda

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) 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.

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) (Omega cm)(-1)), respectively, while the average visible transparency was kept practically constant (approximate to 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 (20 W), within the deposition conditions range which leads to semiconductive material. Such devices presented an I-on (20 V)/I-off (-5 V) ratio of 6 x 10(6) and a field-effect mobility of 0.37 cm(2)/(V s). (C) 2010 Elsevier B.V. All rights reserved.

Phosphorus-doped amorphous silicon thin films, deposited at low temperatures by Plasma Enhanced Chemical Vapour Deposition were used as a dopant source on p-type c-Si substrates. A careful step of dehydrogenation was done in order to maintain the a-Si thin-film integrity. Subsequently, a fine-controlled drive-in of dopant, from the amorphous layer to the crystalline wafer was done, to form the p/n junction, using different time periods and temperatures. Dopant profiling in c-Si wafers as well as dopant concentration in a-Si: H films prior to diffusion, both measured by Secondary Ion Mass Spectrometry, are presented. Junction depths obtained are in the range of 98 nm to 2.4 mu m and surface concentrations are in the range of 1.1 x 10(21) to 4.3 x 10(20) at/cm(3). A dual diffusion mechanism explains the ``kink-and-tail{''} shape found for dopant profile. (C) 2013 Elsevier B.V. All rights reserved.