Preparation and the study optical and electrical properties of thin films for optoelectronic applications

Conductive transparent In 2 O 3 thin films with (222) preferred orientation were prepared by thermal oxidation (TO) in static air of indium thin films at condition (250 ˚ C/25 min). Detailed structural, electrical, and optical characteristics of the film are presented. The data are interpreted to give a direct band gap of (3.6) eV and indirect band gap of (2.5) eV. The In 2 O 3 film has sheet resistance as low as (20) Ω / □ . in absence of any post-deposition annealing conditions. The mobility of these films was estimated to be (31) cm 2 . V - 1 . s -1 .


Experiment 2.1 Film Preparation
High purity (99.999%) indium powder was deposited on an optically flat well-cleaned coring glass substrate at room temperature by using thermal resistive technique under vacuum pressure down (10 - 6 )torr.After film deposition, the substrate was loaded into TO system.Schematic diagram of the TO system is presented as Fig. ( 1) [14].The oxidation process was occurred using tube oven under static air at condition (250˚C/25min).Fig. (2) Display the temperature-time curve for TO process.It is clear that this curve contains three distinct region heating, oxidation cycle and cooling on the other hand, cooling rate of 25˚C/min calculated from coolie's cycle after oxidation process.The In 2 O 3 film thickness was measured and found to be 100 nm.

Film Characteristics
The crystal Structure of In 2 O 3 film was investigated using XRD analysis (Cu K α source; λ= 1.54506 Å) with scan speed of 3 °/min with 2θ mode.The transmittance measurement was performed using spectrophotometer (Shimadzu type) in the spectral range 300-900nm.To measure the electrical properties, ohmic contacts have been made on In 2 O 3 film by depositing of high purity Al film of 500 nm thick through special thin metal sheet mask.Seebeck coefficient measurement was done by measuring of thermovoltage developed under a temperature difference in the interval (5) K.The dark electrical resistivity was measured at room temperature.Moreover, no metallic indium phases are present in the spectrum.The highly oriented film is so important in order to reduce the effect of film texturing on transport properties.The crystal quality of In 2 O 3 film prepared by this method is much better than that film prepared by spray pyrolysis, laser ablation, and DC magnetron sputtering techniques, no highlyoriented plane was a direct and indirect optical energy gaps in the allowed transition were obtained from optical absorption measurements as shown in Fig. (5) and they found to be (3.62)eV and (2.68) eV consequently.These results in good agreement with reported results [1].

Results and Discussion
The room temperature electrical resistivity of the In 2 O 3 film was found to be (2×10 -4 )Ω-cm.The relationship between electrical resistivity and optical transmittance (T) was correlated and derived by Haacke [15].This relationship defined by Figure of Merit (Φ Tc ) which can be given by: Eng.& Tech.Vol..26, No. 7,2008 Preparation and the study optical and electrical properties of thin films for optoelectronic applications Where R s is the electrical sheet resistance measured in thin film.
This parameter could be used efficiently to describe TCO materials.It is obvious from the table that our results are encouraged and competitive to the results obtained by Adurodija et.aL [16].Thermoelectric measurement shows that the In 2 O 3 film has n-type conductivity.Fig. (6) shows the thermovoltage of In 2 O 3 film as a function of the temperature.Seebeck coefficient (S) can be given by equation [19]: Where E fo : is fermi energy.A is a parameter related to the carrier energy.and γ is constant.We plotting 1/s versus 1/T as shown in Fig. (7)

Fig. ( 3 )
Fig. (3) Show a photograph In 2 O 3 film deposited on glass substrate, it is uniform, transparent (around 80% in the visible and NIR regions) and smooth film.The film has good adhesive properties.The XRD spectrum of In 2 O 3 film is presented in Fig. (4).There is strong and sharp single diffraction peak at 2θ = (30.6).It can be indexed to the (222) crystal plane of bcc structure with a = (10.104)Å, which is very close to the ASTM Powder Diffraction Data Card No. ASTM-6-0416.Moreover, no metallic indium phases are present in the spectrum.The highly oriented film is so important in order to reduce the effect of film texturing on transport properties.The crystal quality of In 2 O 3 film prepared by this method is much better than that film prepared by spray pyrolysis, laser ablation, and DC magnetron sputtering techniques, no highlyoriented plane was a direct and indirect optical energy gaps in the allowed transition were obtained from optical absorption measurements as shown in Fig.(5) and they found to be (3.62)eV and (2.68) eV consequently.These results in good agreement with reported results[1].The room temperature electrical resistivity of the In 2 O 3 film was found to be (2×10 -4 )Ω-cm.The relationship between electrical resistivity and optical transmittance (T) was correlated and derived by Haacke[15].This relationship defined by Figure of Merit (Φ Tc ) which can be given by: