Physics and Engineering Physics

The influence of high energy electron (HEE) irradiation from a Sr-90 radio-nuclide on ntype Ni/4H-SiC samples of doping density 7.1 Â 10 15 cm À 3 has been investigated over the temperature range 40-300 K. Current-voltage (I-V), capacitance-voltage (C-V) and deep level transient spectroscopy (DLTS) were used to characterize the devices before and after irradiation at a fluence of 6 Â 10 14 electrons-cm À 2 . For both devices, the I-V characteristics were well described by thermionic emission (TE) in the temperature range 120-300 K, but deviated from TE theory at temperature below 120 K. The current flowing through the interface at a bias of 2.0 V from pure thermionic emission to thermionic field emission within the depletion region with the free carrier concentrations of the devices decreased from 7.8 Â 10 15 to 6.8 Â 10 15 cm À 3 after HEE irradiation. The modified Richardson constants were determined from the Gaussian distribution of the barrier height across the contact and found to be 133 and 163 A cm À 2 K À 2 for as-deposited and irradiated diodes, respectively. Three new defects with energies 0.22, 0.40 and 0.71 eV appeared after HEE irradiation. Richardson constants were significantly less than the theoretical value which was ascribed to a small active device area.

Growth conditions, structural, and optical properties of MgO nanostructure have been investigated. Surface composition and shift in binding energy of Mg at 50.8 eV due to oxidation were examined by core-level spectroscopy. The SEM showed that the film is dense, and grain growth and crystallinity are enhanced by post-deposition annealing. Grain distribution was appraised within the confinement of 24.51 μm 2 from the selected scan areas. X-ray diffraction studies indicated prominent peaks, which are attributed to (111), (200), and (220) reflections from fairly crystallized and randomly oriented MgO thin film. Plane (111) is found to be the preferred orientation of the film. The film transmitted well across the visible spectrum and the estimated energy band gap is 5.41 eV. Absence of catalyst in the electrolyte solution aided the purity of the sample.

Cu2 O thin film and a transparent bilayer have been fabricated by electrodeposition method. The growths were obtained in potentiostatic mode with gradual degradation of anodic current. X-ray diffraction (XRD) study showed that the bilayer is polycrystalline and it possesses mixture of different crystallite phases of copper oxides. Surface morphology of the films was investigated by scanning electron microscopy (SEM). The SEM images revealed that the films were uniformly distributed and the starting material (Cu2 O) had cubical structure. Grains agglomeration and crystallinity were enhanced by annealing. Optical studies indicated that all the samples have direct allowed transition. Energy band gap of the bilayer film was reduced by annealing treatment thus corroborating quantum confinement upshot.

The single solid source precursors, bis-(morpholinodithioato-s,s')-Pb and bis-(morpholinodithioato-s,s')-Pb-Cd were prepared by direct reaction of metal chloride solution and ammonium morpholinodithiocarbamate. Lead sulphide and lead cadmium sulphide thin films were deposited on sodalime glass substrates using Metal Organic Chemical Vapour Deposition (MOCVD) technique. Preparation of the films was achieved by the pyrolysis of the prepared precursors at 400 °C with a flow rate of 2.5 dm 3 /min for 2 hours deposition period. The deposited films were characterized using Ultraviolet-Visible spectroscopy, X-ray Diffractometry (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray spectroscopy (EDX). A direct optical band gap of 0.46 eV was obtained from the analysis of the absorption spectrum for lead sulphide and 2.17 eV for lead cadmium sulphide thin films. XRD revealed that both films are polycrystalline in nature, with face-centred cubic phase in PbS film and the presence of cubic and hexagonal phases of CdS and cubic phase of PbS in the PbCdS film. SEM micrographs also revealed polycrystalline nature with uniformly distributed grain estimated to be less than 1 µm in size for both films. It also showed that both films have textured surfaces. The EDX showed that both deposited films are nonstoichiometric and are cation deficient.

Room temperature growth of nanocrystalline TiO 2 thin film was carried out by two-electrode cell. The film was characterized by surface probing techniques. Morphological studies revealed that film's grains are evenly distributed across substrate surface. Average height of grains distribution is below 64 nm. Post-deposition annealing aided film's particles' orientation in a structure that resulted in compact layer. Average crystallite size was estimated as 19.5 nm. Quality and chemical states of film composition were observed by core level photoemission studies. From XPS studies, small shift (∼0.11 eV) observed in binding energy position of Ti 2p 3/2 corroborated oxidation states of titanium species found in TiO 2 structure. Peak broadening and formation of In O Sn linkage at oxygen valence band indicated interactions between substrate's atoms due to annealing. Apart from substrate's atoms interaction, chemical state of Ti profile remained stable implying no major chemical interaction between ITO atoms and film components. This study demonstrated TiO 2 as a recipe for stable barrier layer capable of hindering charge trapping in nanostructured photonic devices.

Growth conditions, structural, and optical properties of MgO nanostructure have been investigated. Surface composition and shift in binding energy of Mg at 50.8 eV due to oxidation were examined by core-level spectroscopy. The SEM showed that the film is dense, and grain growth and crystallinity are enhanced by post-deposition annealing. Grain distribution was appraised within the confinement of 24.51 μm 2 from the selected scan areas. X-ray diffraction studies indicated prominent peaks, which are attributed to (111), (200), and (220) reflections from fairly crystallized and randomly oriented MgO thin film. Plane (111) is found to be the preferred orientation of the film. The film transmitted well across the visible spectrum and the estimated energy band gap is 5.41 eV. Absence of catalyst in the electrolyte solution aided the purity of the sample.

Magnesium sulphide (MgS) thin films have been successfully grown by electrochemical deposition process at room temperature. X-ray diffraction studies revealed that the films have distinct features of crystallin-ity. Prominent characteristic peaks corresponding to cubic structure were identified along (200) and (222) reflections. Surface morphology indicated that the grain sizes of the films ranging between 15 and 17 nm were uniformly distributed across the substrate. Post-deposition annealing enhanced the shape and particle size of the films. Growth height and surface roughness were obtained from atomic force microscope topographic images. Analysis of the optical data gave the values of energy band gaps of the three MgS thin films under study. Energy gaps of the annealed samples were estimated as 3.54 and 3.73 eV while that of as-deposited was given as 4.10 eV.