Sohail A. Khan

Structural and optical properties of ITO/TiO2 anti-reflective films for solar cell applications

Indium tin oxide (ITO) and titanium dioxide (TiO2) anti-reflective coatings (ARCs) were deposited on a (100) P-type monocrystalline Si substrate by a radio-frequency (RF) magnetron sputtering. Polycrystalline ITO and anatase TiO2 films were obtained at room temperature (RT). The thickness of ITO (60 to 64 nm) and TiO2 (55 to 60 nm) films was optimized, considering the optical response in the 400- to 1,000-nm wavelength range. The deposited films were characterized by X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), and atomic force microscopy (AFM). The XRD analysis showed preferential orientation along (211) and (222) for ITO and (200) and (211) for TiO2 films. The XRD analysis showed that crystalline ITO/TiO2 films could be formed at RT. The crystallite strain measurements showed compressive strain for ITO and TiO2 films. The measured average optical reflectance was about 12% and 10% for the ITO and TiO2 ARCs, respectively.

Group Theory in Geometrical Optics

We show under what conditions the transformations in the paraxial region from the object space to the image space by combination of lenses in air forms a continuous group. First the case of a single lens is treated. Here the concept of the middle point and its shift is introduced. Using this, the condition to form a group is obtained. Next, the case of two lenses separated by a distance is considered. Using the middle point concept, the condition to form a group is found. The condition turns out to be that the separation between the principal planes in the first case and that of the equivalent lens in the second case be zero. Finally it is concluded that the only condition for the transformation to form a group irrespective of the number of lenses employed is that the separation between the principal planes be zero.

Process optimization of doping conditions for (100) P-type monocrystalline silicon solar cell using response surface methodology

Abstract. The effect of time and temperature on the sheet resistance (RS) and carrier concentration (NA) of (100) P-type monocrystalline Si was investigated. Phosphorus-doped n+-emitters were fabricated through solid-source doping in a quartz tube furnace. The process variable values for 13 runs were proposed by response surface methodology (RSM). The optimized values for time and temperature predicted by RSM were 56 min and 1045°C, respectively, for a sheet resistance of 41.7  Ω/□ and a carrier concentration of 3.7E18  cm−3. Optimization-based fabrication was found to be in close agreement with the optimized values. Parameter optimization using RSM could be valuable in achieving predetermined dopant variables in optoelectronic devices as well as in reducing the surface recombinations and series resistance of highly efficient Si solar cells.

QUASIMOLECULAR POTENTIAL WITH MODIFICATION

Quasimolecular optical potentials used for identical nuclei have been modified for application to different interacting nuclei. This has been applied to the 28Si–16O system and compared with those results using the Woods–Saxon potential that had been found to reproduce the experimental results. The result indicates that the modification is useful and provides information on nuclear properties and explains the origin of imaginary potential. It has the applicability to a wide range of nuclei.

IWBC ANALYSIS WITH QUASIMOLECULAR OPTICAL POTENTIALS

The quasimolecular optical potential with Incoming Wave Boundary Condition model is used to obtain the fusion and elastic scattering cross-section at the sub-Coulomb region and above. This has been done for the 16O+16O and 12C+12C systems. It is found that sudden potentials describe well the average trend in the fusion and elastic scattering cross-section using the Incoming Wave Boundary Condition Method. Potentials fits for low energy are then used to obtain cross-sections at higher energies. Excellent agreement is obtained for the location of various peaks observed experimentally, especially in the case of 16O+16O. The parameters from these potentials give information on the nuclei in these dynamical situations. We find that a larger radius and a low density in the central region is required to explain the phenomena. The range of Yukawa potentials used are also larger by a factor of two as compared to those used by other authors.

Quasimolecular nuclear potential and its application to 12C +16O reaction near and above the Coulomb barrier

The quasimolecular potential in the sudden approximation is used both near and above the Coulomb barrier (CB) for the 12C +16O system. It is found that the resonances associated with the dinuclear configuration are well produced in energy above the CB. Near and below the CB where adiabatic potential is appropriate, it was found that the potential can also be used, provided the potential parameters are varied and the range parameter of the Yukawa term is increased. Resonance positions for L = 8, 9, 10 and 11 agree with experimental findings. The L = 6 resonance energy and width very near 9MeV and not at 8.8MeV is also reproduced thus supporting experimental results.

Molecular dynamics study of thermal expansion and isothermal compressibility of strontium titanate and barium zirconate

Molecular dynamics simulation has been carried out to study the thermal-physical properties of strontium titanate and barium zirconate ceramic materials. Pairwise interactions, which consist of Coulombic interaction, short-range repulsion, Van der Waals attraction and Morse-type covalent bonding, have been adopted to represent the intricate interatomic interactions. Structural properties, thermal expansion and isothermal compressibility of the perovskite ceramic materials have been calculated in the temperature range of 298 K – 2000 K and pressure ranging from 1 atm to 20.3 GPa. Comparisons between the ceramic materials suggest that strontium titanate is more expansible but less compressible than barium zirconate. The simulation results show good agreement with the experimental data.

Resonance Parameters of Quasibound States For Diatomic Molecules

Methods used previously for quasibound states of not so heavy, heavy‐ion nuclear systems are applied to obtain information on diatomic molecules at the atomic level. Such calculations agree with the results obtained by authors using other methods over the entire range from J = 4 to 38. In this process besides obtaining resonance energies and widths, the energy shifts due to virtual transitions into the continuum are also obtained.

Band gap calculation for two layered perfect conductor (PEC) electromagnetic band gap structure in application of microstrip

The object of this paper is to calculate the band gap energy of the newly designed waveguide structure. The structure used was 2 layers of perfect conductor (PEC) sandwiched with an electromagnetic band gap (EBG) or photonic crystals (PC) in the center. The lattice arrangement of the EBG was square lattice. The cylinder rods is made of PEC also and separated with each other at 1 mm. The size of the cylinder is 0.43 mm in radius. The cylinder rods were embedded in FR-4 which has dielectric constant 4.9. We designed the structure and simulate it in CST Microwave Studio (MWS). We performed a parametric phase sweep in eigenmode. The band energy was studied and analyzed.

Characteristic of 2D triangular lattice of photonic crystals for microwave and photonic devices

The object of this paper is to study the fundamental characteristic of the 2 dimensional triangular lattice photonic crystals. The structure we studied consisted of a periodic array of dielectric rods in a dielectric slab. This structure has a certain forbidden gap which can be found by solving the Maxwell Equation. In this paper, we studied the frequency independent material for finding the dispersion curves using the plane wave expansion method. For the application in microwave and photonic devices, the scattering parameters of the structure must be studied. We used CST Microwave Studio to analyze the scattering parameters and the result is discussed. We also investigated the effect of different background material.