Koteswara Rao Peta

Behavior of temperature dependent electrical properties of Pd/Au Schottky contact to GaN grown on Si substrate by MBE

We investigated the effect of temperature on the behavior of electrical properties of Pd/Au Schottky contact to GaN/Si (111) in the temperature range of 125–325 K in steps of 25 K using current–voltage (I–V) and capacitance–voltage (C–V) analysis. The Schottky barrier height ( I–V ) and ideality factor is calculated using standard thermionic emission theory. The value of I–V was found to increase from 0.41 ± 0.002 eV to 0.79 ± 0.008 eV when temperature varied from 125 to 325 K. The ideality factor of diodes also decreased from 5.91 ± 0.01 to 1.03 ± 0.05 with increase in temperature. The series resistance (R s) is calculated using Cheungs method and it is observed that the value of R s decreased from 74.40 ± 0.32 Ω to 58.59 ± 0.11 Ω when the temperature increased from 125 to 325 K. Barrier height ( C–V ) and effective carrier concentration (Nd ) is also reported from C–V characteristics as a function of temperature and the value of C–V was found to decrease with increase in temperature. The behavior of barrier heights obtained from I–V and C–V characteristics is different due to difference in the nature of measurement techniques. The deviation of conventional Richardsons constant from theoretical value of GaN is due to unusual behavior of temperature dependent electrical properties and barrier inhomogeneity. This is successfully explained by assuming the double Gaussian distribution of inhomogeneous barrier heights of Au/Pd/GaN/Si Schottky diode.

Effect of lattice strain on structural and optical properties of ZnO nanorods grown by hydrothermal method

In this work, we have synthesized ZnO nanorods over ZnO seeds/ITO/glass substrate by the facile hydrothermal method. ZnO seeds are grown at different temperatures ranging from 150°C to 550°C in steps of 100°C. We have studied the effect of strain on the structural and optical properties of ZnOnanorods. It was observed that the growth temperature of seed layer has an influence over the lattice strain present in the nanorods. The as synthesized nanorods were characterized by scanning electron microscope (SEM), x-ray diffraction (XRD) and photoluminescence (PL). SEM images confirm the formation of dense arrays of vertically aligned nanorods on seeds which are grown at 350°C. In addition to this, XRD patterns reveal that these ZnO nanorods are preferentially oriented along (002) direction. The strain analysis based on the XRD results reveals that the minimum value of strain is obtained at 350°C which is attributed to the improved crystalline quality of the interface of seed layer and nanorods leading to their...

Effect of incorporation of silver nanoparticles in PEDOT:PSS layer on performance of organic solar cell

Solution processable organic solar cells have attracted significant interest in scientific community due to their easy processability, flexibility and eco friendly fabrication. In these organic solar cells structure, PEDOT:PSS layer has major importance as it used as hole transporting layer. In the present work, we have analyzed the effect of incorporation of silver nanoparticles (AgNPs) in PEDOT:PSS layer for P3HT:PCBM based organic solar cells. The presence of Ag nanoparticles in PEDOT:PSS film is confirmed by atomic force microscopy (AFM) images. It has been observed that PEDOT:PSS layer with AgNPs has ∼5.4% more transmittance than PEDOT:PSS layer in most of the visible region, which helps in reaching more light on active layer. Finally, solar cell with structure ITO/PEDOT:PSS:AgNPs/Al is fabricated and J-V characteristics are plotted under illumination. It is observed that there is a significant (∼10%) enhancement in short circuit current and slight increment in open circuit voltage with addition of A...

Suppression of trap assisted non-geminate recombination by incorporation of multilayer graphene in P3HT:PCBM for stable and efficient photovoltaic device

In the present work, multilayer graphene (MLG) has been demonstrated to be a promising material for improvement in power conversion efficiency (PCE) as well as stability of the polymer based photovoltaic (PV) devices. MLG, when incorporated into the active layer of the P3HT:PCBM based PV device provides additional 2D pathways for long distance electron transport, avoiding interaction with holes and hence leading to suppression of non-geminate recombination in the device. PCE of the device is shown to improve by ~ 54% due to improvement in absorbance as well as by reduction in non-geminate recombination leading to ~ 8.9% increase in short circuit current density. Also, open circuit voltage improves by ~ 13.75% owing to increase in the fermi-level splitting due to large number of charge accumulated at the electrodes. MLG also reduces the rate of degradation of the device by the factor of ~ 1.5 by suppressing the effect of generation of deep trap levels in the active layer which in turn results in improving the stability of the device.

Controlling the Morphology of ZnO Nanostructures During Growth Process

In the present work, Zinc Oxide (ZnO) nanorods and nanotubes were fabricated in single synthesis step by hydrothermal method over ITO/glass. We have studied the growth mechanism behind the formation of ZnO nanotubes from nanorods. Finally, a control over the morphology of ZnO nanostructures during the growth process has been achieved. The as-synthesized nanorods and nanotubes were structurally characterized by field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) . Structural characterization confirms the formation of dense arrays of ZnO nanorods and nanotubes with a hexagonal crystal structure .

Electrical and structural properties of (Pd/Au) Schottky contact to as grown and rapid thermally annealed GaN grown by MBE

We studied effect of thermally annealed GaN surface on the electrical and structural properties of (Pd/Au) Schottky contact to Ga-polar GaN grown by molecular beam epitaxy on Si substrate. Current voltage (I-V) measurement was used to study electrical properties while X-ray diffraction (XRD) measurement was used to study structural properties. The Schottky barrier height calculated using I-V characteristics was 0.59 eV for (Pd/Au) Schottky contact on as grown GaN, which increased to 0.73 eV for the Schottky contact fabricated on 700 °C annealed GaN film. The reverse bias leakage current at -1 V was also significantly reduced from 6.42×10−5 A to 7.31×10−7 A after annealing. The value of series resistance (Rs) was extracted from Cheung method and the value of Rs decreased from 373 Ω to 172 Ω after annealing. XRD results revealed the formation of gallide phases at the interface of (Pd/Au) and GaN for annealed sample, which could be the reason for improvement in the electrical properties of Schottky contact a...

Optical absorption and emission characterization of P3HT: graphene composite for its prospective photovoltaic application

In the present work, regioregular P3HT (Poly (3-hexylthiophene-2, 5-diyl) was blended with graphene nanopowder and the optical spectroscopic characterization of the composite has been performed. It was observed that at low concentration of graphene (up to 0.1 wt %) there is no significant variation in absorption intensity or wavelength range. But at higher concentration (> 0.1 wt %) the absorption intensity starts reducing. Whereas, the photoluminescence of the composite solution quenches as we increase the concentration of graphene. It reveals that charge recombination decreases with increase in concentration (0.05 to 0.5 wt %) of graphene. Therefore 0.1 wt % seems to be the optimized concentration of graphene in the composite for which appropriate quenching of PL was observed without any significant reduction in absorption of photons. Thus maximum efficiency in P3HT: graphene composite photovoltaic cell is expected for 0.1 wt % of graphene concentration in our typical case.