Ali Rakhshani | Kuwait University (original) (raw)

Papers by Ali Rakhshani

Research and reviews: journal of material sciences, Oct 11, 2017

Applied Physics A, 2004

... Phys. A 79, 20212025 (2004) Materials Science & Processing Applied Physics A AE RAkHSHAN... more ... Phys. A 79, 20212025 (2004) Materials Science & Processing Applied Physics A AE RAkHSHANI u b. PRADEEP Thin films of ZnTe electrodeposited on stainless steel ... Phys. 66, 219 (2000) 6 T. Mahalingam, VS John, S. Rajendran, PJ Sebastian: Semicond. Sci. Technol. ...

Solid-State Electronics, 1991

ABSTRACT

Journal of Alloys and Compounds, 2016

physica status solidi (a), 2002

Electrodeposition of Cd x Hg 1-x Te films with a thickness of about 1 μm and a bandgap energy in ... more Electrodeposition of Cd x Hg 1-x Te films with a thickness of about 1 μm and a bandgap energy in the range 1.2-1.5 eV (0.87 < x < 1) is investigated. Deposition is performed on stainless steel substrates at 80-90 °C from a bath containing CdSO 4 , TeO 2 and HgCl 2 . Film composition and bandgap energy are evaluated, respectively, from the variation of the deposition current with time and from the spectral response of photocurrent in Schottky devices formed on these films. In addition, other characterization techniques such as XRD, SEM and EDAX are also used. Films grow with a graded composition unless HgCl 2 is added periodically into the solution during deposition. Films consisting of several layers with different thickness and composition can also be deposited. Films consist of grains with an average size of about 100 nm and are less oriented than grains in identically deposited CdTe films.

Journal of Applied Physics, 2001

Solar cells of p-CdTe/n-CdS structure with a conversion efficiency of 10%+/-1% (AM1 spectrum, 127... more Solar cells of p-CdTe/n-CdS structure with a conversion efficiency of 10%+/-1% (AM1 spectrum, 127 mW/cm2 irradiance) were prepared by electrodeposition of CdTe on CdS-coated conducting glass. CdS was coated by chemical bath deposition. The tin-oxide conducting glass was prepared by the spray pyrolysis technique. The current-voltage, capacitance-voltage, photocurrent-voltage, photocurrent spectroscopy, and photoinduced current transient spectroscopy measurements proved to be powerful tools for the characterization of junction. The concentration of donors and acceptors in both sides of the junction are comparable, in the range of 1016 cm-3. The cell built-in potential is 1.20 V from which 0.65 V drops across the depletion width of CdTe. From the analysis of experimental data to construct the energy band diagram, it becomes evident that an electric dipole layer must exist at the CdTe/CdS interface. The presence of this layer is associated with a discontinuity of electrostatic potential at the interface by 0.28 V and a conduction-band spike of 64 meV. The conduction-band spike and an interfacial recombination center are accountable for the collection losses of photogenerated carriers. The recombination center that is likely related to the interstitial cadmium defect is energetically located 0.63 eV below the conduction-band edge and has a capture cross section of 8.8×10-12 cm2.

STUDIES IN HEALTH SCIENCES, 2021

A hanseníase é uma infecção causada pelo Mycobacterium leprae, sendo que o Brasil encontra-se no ... more A hanseníase é uma infecção causada pelo Mycobacterium leprae, sendo que o Brasil encontra-se no segundo lugar globalmente entre os países com os maiores números de casos. Seu tratamento poliquimioterápico tem duração de seis (paucibacilar) ou 12 meses (multibacilar). Utiliza as medicações rifampicina, dapsona e clofazimina, combinadas com posologias de acordo com o tipo da doença e peso dos pacientes. Leprosy is an infection caused by Mycobacterium leprae, and Brazil is in second place globally among the countries with the highest number of cases. Its multidrug therapy treatment lasts six (paucibacillary) or 12 months (multibacillary). It uses the medications rifampicin, dapsone and clofazimine, combined with dosages according to the type of disease and weight of the patients.

Aligned ZnO nanorods grown on polycrystalline substrates have promising optoelectronic applicatio... more Aligned ZnO nanorods grown on polycrystalline substrates have promising optoelectronic applications. Novel samples with such structures were electrodeposited on stainless foil from a ZnCl2 route. Well-aligned and free-standing hexagonal nanorods with 100 nm diameter and closely-packed microrods with a diameter above 1 μm could be grown normal to the substrate. The optical transition energies (absorption and emission) of samples were determined by transmittance and photoluminescence spectroscopy. We report on the fabrication of high-quality AgSchottky diodes formed on the oxygen-treated (002) facets of microrods. Diodes with a large barrier height (1.1 eV), low saturation current density (1.3 pA/cm) and high rectification factor (5 × 10 at ±3 V) were fabricated. The concentration and mobility of free electrons in oxygen-treated microrods were measured as 1.4× 10 cm and 1.2 cmVs, respectively.

Successive chemical solution deposition (SCSD) of ZnO on p + -Si wafer is investigated. In certai... more Successive chemical solution deposition (SCSD) of ZnO on p + -Si wafer is investigated. In certain conditions continuous and compact ZnO nano-rods, forming a film, can be grown on the wafer. Light-emitting heterojunction p-n diodes are fabricated and their optoelectronic properties are studied.

kuwait journal of science, 2014

Nitrogen-doped ZnO (ZnO:N) films were prepared by the reactive magnetron sputtering technique usi... more Nitrogen-doped ZnO (ZnO:N) films were prepared by the reactive magnetron sputtering technique using a zinc target. The effect of thermal annealing in different ambient on the films composition, chemical bonding states, structure, optical transmittance and photoconductivity was investigated. The as-grown films are composed from 9-nm large grains with strained unit cell. The annealing process relaxes the strain and increases the grain size to 39 nm. Annealing also increases the direct band gap of the film from 2.42 eV to 3.26 eV. The as-grown and annealed films show photoconductivity in the visible region which is partly due to the effect of a nitrogen-related defect level with the ionization energy of 1.71 eV. The conversion of the as-grown n-type films to p-type ZnO was achieved by annealing the films in air. The converted p-ZnO and electrodeposited n-ZnO films were used in the fabrication of light-emitting homojunction diodes. Diodes with a reasonably good current-voltage rectifica...

International Journal of Electrochemical Science

Journal of Materials Science: Materials in Electronics

Cu2ZnSnS4 (CZTS) is a promising light absorber photovoltaic material due to its p-type conductivi... more Cu2ZnSnS4 (CZTS) is a promising light absorber photovoltaic material due to its p-type conductivity, optimum direct band gap, high optical absorption coefficient, and the fact that it is composed from the abundant and non toxic elements. Among different preparation techniques, solution based routes are attractive due to their simplicity and low cost aspects. In this work the precursor Cu–Zn–Sn metallic alloy films were co-electrodeposited at the threshold cathode potential of −1.10 V (vs. Ag/AgCl reference electrode) on both molybdenum and ITO-coated glass substrates from the bath solutions containing 20 mM of copper, 10 mM of tin, 500 mM of tri-sodium citrate and different high zinc concentrations in the range of 200–600 mM. This approach of using high zinc concentrations in the bath solution and utilizing the least negative cathode potential in order to minimize the film porousity has not been adopted previously. The precursor films were converted to CZTS by a sulfurization process. We studied the effect of high Zn concentration in the bath solution on the composition, structure, morphology, and optical characteristics of the CZTS films using scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction, Raman spectroscopy, and optical transmittance spectroscopy. Non-porous and uniform near-stoichiometric and phase-pure stoichiometric CZTS films could be synthesized from the precursor films deposited from the 600-mM Zn-containing solution at 25 and 60 °C, respectively.

Journal of Alloys and Compounds

Abstract Formation of nitrogen-doped p-type ZnO (p-ZnO) and related homojunction devices has been... more Abstract Formation of nitrogen-doped p-type ZnO (p-ZnO) and related homojunction devices has been reported extensively using a variety of techniques with the exception of thermal oxidation of ZnON that is a simple and less explored method. We converted sputter-deposited ZnON films to p-ZnO at relatively low oxidation temperatures (400–500 °C) as compared with other reports. Chemical bonding states of nitrogen in p-ZnO films were examined by XPS analysis and the mechanism of p-type doping was discussed. Films were characterized by XRD, SEM, photocurrent spectroscopy, and photoluminescence (PL) measurement. Films were composed from nano-size crystallites with (100) preferential orientation. A shallow acceptor level with a 70–90 meV binding energy and a 1.72-eV deep level were measured and identified. PL thermal quenching of the films had activation energy of 34 meV. Schottky barrier (SB) and homojunction diodes, with two different types of n-ZnO, were fabricated on films and their parameters were compared with the reported data. The SB and both types of homojunction diodes had high rectification factors (10 4 -10 5 ) and good device parameters. The conductance of homojunction diode based on sputter-deposited n-ZnO showed thermal activation energies of 0.08–0.12 eV, 0.16–0.20 eV, and 0.40–0.50 eV. The homojunction diode based on n-ZnO nano-rods exhibited strong electroluminescence in the visible region from which two defect-related transition energies of 2.21 eV and 2.66 eV were obtained. In conclusion, good quality p-ZnO films and related devices can be prepared by thermal oxidation of ZnON films.

Journal of Electronic Materials, 2015

The deposition of device quality Cu2ZnSnS4 (CZTS) films on flexible substrates by simple and cost... more The deposition of device quality Cu2ZnSnS4 (CZTS) films on flexible substrates by simple and cost-effective techniques is of great interest for solar cell applications. In this work, CZTS films were deposited on lightweight flexible substrates by successive dip coating using a nontoxic, methanol-based precursor solution. The films were characterized by x-ray diffraction, energy dispersive x-ray analysis, scanning electron microscopy, atomic force microscopy, optical transmission spectroscopy, photocurrent spectroscopy and admittance spectroscopy. The films prepared by this technique have direct band gaps of 1.5–1.6 eV, a p-type resistivity of ~1 Ω cm, an acceptor concentration of ~1017 cm−3 and structural and morphological properties that are suitable for device applications. Four defect levels with activation energies of 5.4 meV, 18.8 meV, 70 meV, and 221 meV were detected in the films. All but the shallowest defect level were attributed to the native VCu, CuZn, and VSn acceptor-type defects. For further assessment of the films, Schottky barrier and heterojunction diodes were fabricated and characterized. The results signified that the device quality CZTS films can be synthesized by the dip-coating method used in this study.

Applied Surface Science, 2014

Abstract Heterojunction devices were prepared from ZnO films grown by successive chemical solutio... more Abstract Heterojunction devices were prepared from ZnO films grown by successive chemical solution deposition on flexible stainless steel substrate and from p-type polymer films of PEDOT:PSS. The effect of air annealing and H 2 O 2 treatment of ZnO on the optoelectronic properties of devices were investigated. Various techniques were utilized for the characterization of ZnO films and the evaluation of devices. Devices with diode type current–voltage and capacitance–voltage characteristics can be fabricated if the hydroxyl content of the as-grown ZnO is removed by annealing the film in air (400 °C, 20 min). H 2 O 2 treatment of ZnO for 10 min followed by air annealing yields a high resistivity interfacial layer required for the device to exhibit visible electroluminescence. A typical light emitting diode shows a current rectification factor of ∼100 (±2 V), ideality factor of 3.0, barrier height of 1.1 eV and reverse-bias breakdown voltage of −36 V. Fabricated diodes show self-powered visible-blind UV photodetection characteristics in the wavelength range of 274–375 nm.