Thin Film Technology

A Schottky barrier on GaN film grown on Si (111) substrate by low cost electrochemical deposition technique at 20 °C was obtained and characterized. Pd was used as a Schottky barrier contact. The temperature dependent current-voltage (I-V-T) curves have been measured on Pd/GaN contacts in the range of 300-470 K. Thermionic emission theory has been applied to the curves and the Schottky barrier heights, ?B0, and ideality factors, n, have been calculated. Barrier heights and ideality factors are evaluated as functions of temperature. These measurements indicate that the Schottky barrier height increases and ideality factor decreases with increasing temperature. The apparent Richardson constant was found to be 2.38x10-7Acm-2K-2 and mean barrier height of 0.3 eV. After barrier height inhomogeneities correction, by assuming a Gaussian distribution (GD) of the barrier heights, the Richardson constant and the mean barrier height were obtained as 19.3 Acm-2K-2 and 1.54eV, respectively. The corrected Richardson constant was very closer to theoretical value of 26Acm-2K-2.

Rhizobium and Azotobacter are agriculturally beneficial living organisms present in biofertilizers which colonize the rhizosphere, fix atmospheric nitrogen into Ammonia and increases soil fertility thereby promote plant growth. Increased exposure of UV light has specific effect on various life forms. UV radiations kill or inactivate microorganism thereby prevent the growth and development of the plants. Titanium dioxide (TiO2) is a wide band gap semiconductor, an efficient light harvester and has strong UV light absorbing capability. Here, we studied the UV screening effect of TiO2 thin films as a protective layer in the enhancement of growth of Rhizobium and Azotobacter. TiO2 thin films of different thicknesses were deposited on the glass substrates using TTIP as precursor by sol-gel dip coating technique by repeating the number of coating cycles which were annealed at 550o C for one hour. The structural properties, surface morphology, stoichiometry and optical properties were characterized by XRD, SEM, EDAX, AFM and UV-Visible studies. The relation of survival rate of microorganism and thickness of the thin films was studied in detail. It is found that the crystallite size increases (21.3 nm-77.6 nm), band gap decreases (3.4eV-2.8eV) and transmittance decreases with increase in film thickness. We have observed that survival rate of organisms increases with increase in film thickness. This study showed that TiO2 thin films act as protective layer against UV radiation and enhance the survival rate of organisms.

The effects of annealing on the structural, morphological and optical band gap of chemically deposited cadmium selenide (CdSe) thin films have been investigated. The X-ray diffraction analysis revealed that both the as-deposited and annealed CdSe thin films had three major peaks corresponding to the cubic structure of CdSe with a preferred orientation along the (111) plane. After annealing, the intensity of the major peaks became more pronounced and a new low intensity peak was observed. There was also a slight shift in peak positions towards smaller 2? angles. The average crystallite size increased after annealing whereas the microstrain and dislocation density decreased. The SEM micrographs of the annealed thin film showed a slight improvement in crystallinity and uniformly distributed all over the surface of the substrate without voids. The optical energy band gap of the thin films decreased from 1.86 eV to 1.74 eV after annealing.

The spin coating method was used for the preparation of ZnS, Mn doped ZnS (MZS) and Cobalt doped ZnS (CZS) thin films and their structural and optical properties were studied. The ZnS thin films were grown on well cleaned glass substrates by spin coating method from aqueous solution of Zinc Sulphide and Thiourea with two different dopants Mn and Co. The properties of ZnS, MZS and CZS thin films and their growth mechanisms were studied using x-ray diffraction, UV-Visible spectroscopy, photoluminescence and VSM studies. Effect of dopants on structural, optical and magnetic properties was reported. Keywords: ZnS, Spin Coating, Dopants, Structural, Optical and magnetic properties.

In this work Cadmium Sulphide/Porous Silicon (CdS/PS) nanocomposite structure was successfully synthesized by depositing CdS film over PS substrate at room temperature. CdS was incorporated into the pores of PS and thereby making a protecting layer. The XRD, SEM, FTIR and PL analysis were carried out to characterize the CdS/PS structure. XRD result suggests the formation of CdS hexagonal structure on PS surface. The diffraction peaks pertaining to PS along with those corresponding to CdS were observed. The surface morphology of the prepared CdS/PS layer was studied by SEM analysis. The information about the vibration and rotation of molecular groups and the bonding of inorganic molecules on silicon surfaces are confirmed by transmission FTIR spectra. The PL measurements on CdS/PS structure show emission peaks at around 620 & 660 nm with 2.0 & 1.9 eV band gap respectively. These results show the incorporation of CdS into the pores of PS and capable of utilizing for device applications. Keywords: CdS/PS, XRD, SEM, FTIR, PL

Good featured glassy bismuth selenide (Bi2Se3) thin films were prepared from solutions having bismuth nitrate, triethanolamine and sodium selenosulphate at room temperature by chemical bath deposition technique. The crystalline structure, surface morphology, electrical and optical properties of these Bi2Se3 thin films were investigated as a function of annealing process. X-Ray diffraction studies resulted in Bi2Se3 thin films with amorphous structure at room temperature (RT) and growth in film was found by annealing with hexagonal crystal structure. A uniform sphere-like morphology was observed from scanning electron microscopy upon annealing. Optical absorption studies revealed that a direct band gap of 1.11 eV for as-deposited Bi2Se3 films and is drops to 1.02 eV by annealing in air at 2000C for one hour. Moreover the absorption edge shifting toward longer wavelength associated with crystallinity development of annealed film. As-deposited, the thin films show resistivity of approximately 6k?/cm2 decreases upon annealing. From temperature-resistance measurements Bi2Se3 thin films are distinctive semiconductor material upon annealing, with calculated activation energies of 0.18eV and 0.9eV at lower and higher temperature respectively. In photoconduction studies after annealing, the films display organized rise in the photocurrent with applied voltage than in the as-prepared films. This enrichment in conductivity results from crystallinity development along with partial loss of selenium. This may accelerate various promises for the usage of these films by chemical bath deposition method.

Thin-film ruthenium oxide electrodes are prepared by sol-gel spin coating technique on a stainless steel substrate. To obtain different film thicknesses deposition coats are increased. Thin films are used as electrodes for supercapacitor application with 0.1 M KOH electrolyte. Film thickness affected on the specific capacitance and charge–discharge. A maximum specific capacitance of 489 F/g is achieved with an electrode thickness of 0.1mg/ cm2. These results are explained by considering the structural and morphological changes that take place with increasing film thickness. The energy efficiency decreased with increasing film thickness. RuO2 film can withstand about 1000 cycles without a significant decrease in the capacitance. The EIS analysis data gave low value of ESR for 4 coats.

Lead sulphide (PbS) thin films have been deposited on glass slide substartes by chemical bath deposition technique from an aqueous alkaline bath containing lead nitrate [Pb(NO3)2]and thiourea [SC(NH2)2]. The influence of bath temperature on the properties of the films were investigated . The structural, surface morphological and optical properties of films were studied by X-Ray diffraction, scanning electron microscopy and UV-Vis spectroscopy, respectively. The X-Ray diffraction studies reveal that the PbS films were polycrystalline in nature with preferrential orientation along (200) plane. The scanning electron microscopy results indicate that the films were smooth, uniform and adherent to the substrate. The band gap energy was decreased from 1.2 eV to 0.9 eV as the bath temperature was increased from 30 OC to 60 OC. The films deposited at 60 ^OC have shown good crystallinity and uniformly distributed over the surface of substrate with larger grain sizes. Therefore, the optimum bath temperature is 60 ^OC.

Report demonstrates pulse laser dependence CdS thin films thickness variation and properties. Variable thickness properties like; surface morphology, cross sectional view, EDS with elemental mapping, AFM surface roughness parameter, Raman spectrum, photoluminescence, UV-Visible range FT-IR, I-V and R-V characteristics is discussed. It has been noticed with increasing laser pulses thickness, structure, surface morphology, Raman spectra, FT-IR band, I-V and R-V characteristics are changed. With the increasing number of laser pulses, the increase in surface roughness parameter, shift in FT-IR band tail toward the lower wave number side and higher current growth with lower resistance is observed for the thicker films.

We have synthesis manganese sulfide nano-crystalline (n-MnS) powder using manganese acetate and thiourea, trisodium citrate, from chemical route at different pH. The formation of MnS has been confirmed with help of infrared (IR) spectroscopy by observing bands corresponding to the multi phonon absorption. We have also observed the IR bands at 1403 and 1560 cm-1 due to symmetric and asymmetric stretching of COO of the capped sodium citrate at MnS nano-crystalline particles. The Size of crystal is determined as 3-5 nm with the help of X-ray diffraction. We also deposited the thin film of MnS on glass substrate from the solution using self- aggregation approach. The film thickness is measured as 366 nm with profile meter. The optical band gap is calculated as 3.1-3.5 eV. Its value is found to depend on pH. We also measured dark and photo- conductivity at different temperatures.