Papers by Author: A.S. Bhatti

Abstract: Gold/Zinc Phthalocyanine/n-Si metal semiconductor contact with organic interfacial layer have been developed and characterized by Current–Voltage-Temperature (I-V-T) measurements, to study its junction and charge transport properties. The junction parameters, of diode ideality factor (n), barrier height (b) and series resistance (R¬S), of the device are found to shift with device temperature. The barrier height and the diode ideality factor are found to increase and the series resistance is found to decrease with increasing device temperature. The activation energy of the charge carriers is found to be 44 meV and the peak of interface state energy distribution curves is found to shift in terms of Ess-Ev value from 0.582 eV to 0.776 eV with increasing device temperature. The data analysis implies that the Fermi level of the organic interfacial layer shifts as function of device temperature by 100 meV in the device temperature range of 283K to 343K. In terms of dominant conduction mechanism, the I-V-T data analysis confirms the fit of data to the relationship log (IV4)  V1/2 for higher device temperatures and the Poole-Frenkel type is found to be the dominant conduction mechanism for the hybrid device.

Abstract: Mn-doped multiferroic BiFeO3 (BFMO) thin films were deposited on LaNiO3(LNO)/SrTiO3(STO)/Si(100) substrates by pulsed laser deposition (PLD) technique. X-ray diffraction (XRD) showed that films were bicrystalline single phase with (110) preferential orientation. Multiferroic top layer and oxide bottom electrode (LNO) epitaxially followed the buffer layer (STO). Oxygen partial pressure during deposition proved to be critical for phase formation, crystallinity and resistivity of the films. Atomic force microscopic (AFM) studies revealed the smooth, dense and crack free surfaces of the films. Cross-section view of the multilayers by field emission scanning electron microscope (FE-SEM) gave their thickness. Mn substitution resulted in the increase of magnetization saturation, coercive field and clarity of hysteresis loop. The magneto-electric (ME) effect was demonstrated by measuring the dielectric response in a varying magnetic field. Optimally deposited BFMO films show saturated P-E loop.

Abstract: Self-assembled nanowires have attracted much attention due to their potential applications in electronics and optoelectronics. A recent interest in Mn catalyzed GaAs nanowires are due to their potential use in spintronic devices at nanoscale. High densities of Au- and Mncatalyzed self-assembled GaAs nanowires (NWs) with diameter in the range of 20 to 200 nm and length of few microns were synthesized by molecular beam epitaxy (MBE) on different substrates at varied substrate temperatures. These nanowires were investigated by means of μ-Raman spectroscopy at room temperature. The Raman spectra from NWs show an energy downshift and a broadening of the LO and TO phonon lines that differ from those of epitaxial GaAs. We suggest that those downshift and broadening are due to the relaxation of the q=0 selection rule in the presence of structural defects in the nanowires. The results indicate that the use of Mn instead of Au as growth catalyst does not affect the structural quality of the nanowires drastically.