M. Mozibur Rahman

Effect of Al Doping on Structural, Electrical, Optical and Photoluminescence Properties of Nano-Structural ZnO Thin Films

The nano-structural Al-doped ZnO thin films of different morphologies deposited on glass substrate were successfully fabricated at substrate temperature of 350 °C by an inexpensive spray pyrolysis method. The structural, electrical, optical and photoluminescence properties were investigated. X-ray diffraction study revealed the crystalline wurtzite (hexagonal) structure of the films with nano-grains. Scanning electron microscopy (SEM) micrographs indicated the formation of a large variety of nano-structures during film growth. The spectral absorption of the films occurred at the absorption edge of ∼410 nm. In the present study, the optical band gap energy 3.28 eV of ZnO decreased gradually to 3.05 eV for 4 mol% of Al doping. The deep level activation energy decreased and carrier concentrations increased substantially with increasing doping. Exciting with the energy 3.543 eV (λ=350 nm), a narrow and a broad characteristic photoluminescence peaks that correspond to the near band edge (NBE) and deep level emissions (DLE), respectively emerged.

Structural and opto-electrical properties of pyrolized ZnO-CdO crystalline thin films

A series of ZnO-CdO thin films of different molar ratios of Zn and Cd have been deposited on glass sub- strate at substrate temperature 360 C by the spray pyrolysis technique at an ambient atmosphere. X-ray diffraction (XRD) studies confirmed the polycrystalline nature of the film and modulated crystal structures of wurtzite (ZnO) and cubic (CdO) are formed. The evaluated lattice parameters, and crystallite size are consistent with literature. Dislocation density and strain increased in the film as the grain sizes of ZnO and CdO are decreased. The band gap energy varies from 3.20 to 2.21 eV depending on the Zn/Cd ratios in the film. An incident photon intensity dependent I -V study confirmed that the films are highly photosensitive. Current increased with the increase of the intensity of the light beam. The optical conductivity and the optical constants, such as extinction coefficient, refractive index and complex dielectric constants are evaluated from transmittance and reflectance spectra of the films and these parameters are found to be sensitive to photon energy and displayed intermediate optical properties between ZnO and CdO, making it preferable for applications as the buffer and window layers in solar cells.

The6Li-nucleus scattering

SummaryThe elastic scattering of6Li from a number of nuclei between12C and208 Pb is studied within the framework of the strong-absorption model of Frahn and Venter over a wide range of beam energy. The parameters thus obtained are used to analyse the angular distribution for the inelastic scattering of6Li leading to the lowest 2+ states in12C,24,26Mg and56,60Ni and the quadrupole deformation parameter Β2 is extracted in each nucleus.

Properties of cadmium-doped tin oxide thin films prepared by spray pyrolysis method

Cadmium doped Tin Oxide Thin Films have been prepared by Spray Pyrolysis Method on glass substrates at 350°C. Structural, electrical and optical properties have been measured. From XRD it is found that films deposited are crystalline in nature with tetragonal structure having lattice constant a=b=3.86 A° and c=5.62A°. Hall effect measurements show that films prepared are of n-type and the carrier concentration (≈1018 cm-3) and room temperature conductivity decreases with the increases in cadmium concentration in the films. Activation energy has been calculated from conductivity measurements and it was found that conduction within the temperature range we have measured is due to hoping of carriers through the spectrum of localized states. Band gap of the un-doped films calculated from transmission spectrum is about 3.1 eV and the value decrease slightly with the addition of cadmium. The refractive index, extinction coefficient, real and imaginary parts of the dielectric constant have been calculated from the optical spectra. The refractive index decreases with photon energy and also decreases slightly with cadmium concentration while extinction coefficient increases with photon energy.

Effect of yttrium(Y) on structural, morphological and transport properties of CdO thin films prepared by spray pyrolysis technique

Cadmium oxide (CdO) and yttrium (Y) doped CdO (Y: CdO) thin films have been prepared onto glass substrate at temperature 300 °C by spray pyrolysis technique. The effects of yttrium (Y) doping on the structural, morphology, optical and electrical properties were studied systematically. The X-ray diffraction (XRD) study confirms that CdO films are polycrystalline in nature with cubic structure having lattice parameter of 0.4658 nm. Surface topographic and nano-structural analysis indicates cluster grain size and porosity decreased substantially with increase of yttrium (Y) content in CdO films. The optical transmittance exhibits excellent optical transparency, with an average transmittance of >70% in the visible range for 2 to 4% yttrium (Y) doping. The optical band gap widens in Y: CdO film from 2.24 to 2.62 eV through Burstein- Moss shift. Hall measurement confirms that material is of n type with a minimum resistivity of 4.7 × 10−4 Ω-cm with carrier concentration of 4.2 × 1021 cm−3 were achieved for 2% yttrium (Y) doping.