Al 2 O 3 thin films find a number of applications in optoelectronics, sensors and tribology. In this paper, we report the preparation and characterization of alumina films prepared by both electron beam evaporation and spray pyrolysis method. The electrical properties of alumina films were determined by measuring (C-V) and (I-V) characteristics in a metal oxide semiconductor (MOS) structure. A relative dielectric constant (ε r ) of 9.6 for spray pyrolysed films and 8.3 for evaporated films was obtained. The breakdown electric field was found to be around 5 and 1 MV/cm, respectively for spray pyrolysed and evaporated films. The refractive index of alumina films by evaporation was found to be 1.71 and 1.61 at 275 and 500 nm, respectively. The optical band gap of spray pyrolysed films deposited at 300• C was found to be in the range of 5.40-5.55 eV. Structural, elemental analysis and stoichiometry of the films was studied by scanning electron microscope (SEM), energy dispersive X-ray analysis (EDAX), Auger electron spectroscopy (AES) and Rutherford back scattering (RBS) spectra.
Transparent conducting tin oxide thin films have been prepared by electron beam evaporation and spray pyrolysis methods. Structural, optical and electrical properties were studied under different preparation conditions like substrate temperature, solution flow rate and rate of deposition. Resistivity of undoped evaporated films varied from 2⋅ ⋅65 × 10-2 Ω Ω-cm to 3⋅ ⋅57 × 10-3 Ω Ω-cm in the temperature range 150-200°C. For undoped spray pyrolyzed films, the resistivity was observed to be in the range 1⋅ ⋅2 × 10-1 to 1⋅ ⋅69 × 10-2 Ω Ω-cm in the temperature range 250-370°C. Hall effect measurements indicated that the mobility as well as carrier concentration of evaporated films were greater than that of spray deposited films. The lowest resistivity for antimony doped tin oxide film was found to be 7⋅ ⋅74 × 10-4 Ω Ω-cm, which was deposited at 350°C with 0⋅ ⋅26 g of SbCl 3 and 4 g of SnCl 4 (SbCl 3 /SnCl 4 = 0⋅ ⋅065). Evaporated films were found to be amorphous in the temperature range up to 200°C, whereas spray pyrolyzed films prepared at substrate temperature of 300-370°C were polycrystalline. The morphology of tin oxide films was studied using SEM. Keywords. Spray pyrolysis; electron beam evaporated films; tin oxide films; transparent conducting coatings; optical and electrical properties.
A large number of thin films of cadmium oxide have been prepared on glass substrates by spray pyrolysis method. The prepared films have uniform thickness varying from 200-600 nm and good adherence to the glass substrate. A systematic study has been made on the influence of thickness on resistivity, sheet resistance, carrier concentration and mobility of the films. The resistivity, sheet resistance, carrier concentration and mobility values varied from 1"56-5-72× 10-3f~-cm, 128-189f~/El, 1"6-3.9× 1021 crn-3 and 0.3-3 cm2/Vs, respectively for varying film thicknesses. A systematic increase in mobility with grain size clearly indicates the reduction of overall scattering of charge carriers at the grain boundaries. The large concentration of charge carriers and low mobility values have been attributed to the presence of Cd as an impurity in CdO microcrystallites. Using the optical transmission data, the band gap was estimated and found to vary from 2.20-2.42 eV. These films have transmittance around 77% and average reflectance is below 2.6% in the spectral range 350-850 nm. The films are n-type and polycrystalline in nature. SEM micrographs of the CdO films were taken and the films exhibit clear grains and grain boundary formation at a substrate temperature as low as 523 K.
Al 2 O 3 thin films were deposited on silicon, steel and nickel substrates to fabricate MOS and MIM devices. The films were prepared by spray pyrolysis method using a spray solution of Aluminium acetyl acetonate dissolved in dimethyl formamide and this solution was sprayed on to the hot substrates at temperatures of 300 and 350 • C. The films were amorphous in nature as detected by XRD. Capacitance versus voltage (C-V), current versus voltage (I-V) and capacitance versus frequency (C-f) measurements were taken for these films. MOS capacitor was used as a humidity sensor using the home made humidity sensor setup. ac capacitance and parallel resistance of the capacitor as a function of humidity were studied. It was found that the capacitance value increases from 0.537 to 2.073 nf with the increase in relative humidity (RH) from 0 to 90% and the resistance decreases from 153 to 93 k with the increase in relative humidity from 20 to 87%. Relative dielectric constant versus temperature measurements were done for the MOS device to check its ferroelectric behavior and its critical temperature was found to be around 66 • C. MIM device was also used as a humidity sensor by measuring capacitance as a function of time by keeping the sensor in a dessicator. The 555 timer circuits were used to check the sensor behavior of the MOS device. Volume resistivity and breakdown electric field of the film deposited on steel were measured and found to be 5 × 10 11 cm and 5 MV/cm, respectively.
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