Basavaraj Angadi

Oxygen plasma treated epitaxial ZnO thin films for Schottky ultraviolet detection

The effects of oxygen plasma treatment on epitaxial ZnO thin films grown by molecular beam epitaxy were studied. The Au–ZnO–In junction exhibiting ohmic behaviour before the treatment gradually changes to a Schottky junction with the increase in oxygen plasma treatment time. The crystallinity and the surface microstructure did not change to any great extent after the treatment. However, the x-ray photoelectron spectroscopy studies show the removal of conductive OH layer from the surface of ZnO films and the current–voltage characteristics of Au–ZnO–In junction exhibit the rectifying behaviour after oxygen plasma treatment. The fabricated Au–ZnO–Au ultraviolet (UV) detector was successfully tested and was observed to be sensitive to the two UV sources used. The photoresponsivities of the UV detector for the irradiation of two different power densities 350 (λ = 356 nm) and 420 µW cm−2 (λ = 254 nm) are 13.5 A W−1, 15.3 A W−1 at 5 V and 128.9 A W−1, 160 A W−1 at 10 V, respectively.

Structural, electrical, magnetic, and electronic structure studies of PrFe1−xNixO3 (x⩽0.5)

We report the x-ray absorption studies on O K, Fe L3,2, Ni L3,2, and Pr M5,4 edges in PrFe1−xNixO3 along with their structural, electrical transport, and magnetization characterizations. All the samples are in single phase having orthorhombic structure with space group Pnma for x⩽0.4. Ni doping at Fe site brings the system in the conducting regime, resistivity decreases from GΩcmto260mΩcm at room temperature, and the magnetic ordering is stabilized. The temperature dependent resistivity follows the semiconducting behavior and fits well with Greaves’ variable range hopping model. The gap parameter is reduced from 2to0.118eV. The materials are in weak ferromagnetic state and magnetization is gradually decreasing with the enhancement of Ni substitution, whereas magnetic anisotropy is reduced substantially. A new feature about 2.0eV lower than the pre-edge of PrFeO3 in O K edge is observed with Ni substitution at Fe site due to the 3d contraction effect and is growing with the increase of Ni substitution. Fro...

Ferromagnetism in 200-MeV Ag+15-ion-irradiated Co-implanted ZnO thin films

Structural, electrical resistivity, and magnetization properties of 200-MeV Ag+15-ion-irradiated Co-implanted ZnO thin films are presented. The structural studies show the presence of Co clusters whose size is found to increase with increase of Co implantation. The implanted films were irradiated with 200-MeV Ag+15 ions to fluence of 1×1012ions∕cm2. The Co clusters on irradiation dissolve in the ZnO matrix. The electrical resistivity of the irradiated samples is lowered to half. The magnetization hysteresis measurements show ferromagnetic behavior at 300K, and the coercive field increases with the Co implantation. The ferromagnetism at room temperature is confirmed by magnetic force microscopy measurements. The results are explained on the basis of the close interplay between the electrical and the magnetic properties.

Single phase formation of Co-implanted ZnO thin films by swift heavy ion irradiation: Optical studies

Low temperature photoluminescence and optical absorption studies on 200MeV Ag+15 ion irradiated Co-implanted ZnO thin films were studied. The Co clusters present in as implanted samples were observed to be dissolved using 200MeV Ag+15 ion irradiation with a fluence of 1×1012ions∕cm2. The photoluminescence spectrum of pure ZnO thin film was characterized by the I4 peak due to the neutral donor bound excitons and the broad green emission. The Co-doped ZnO films show three sharp levels and two shoulders corresponding to 3t2g and 2eg levels of crystal field splitted Co d orbitals, respectively. The ultraviolet-visible absorption spectroscopy also shows the systematic variation of band gap after 200MeV Ag+15 ion irradiation.

Electrical transport, magnetic, and electronic structure studies of Mg0.95Mn0.05Fe2−2xTi2xO4 ± δ (0≤x≤0.5) ferrites

We present structural, electrical transport, magnetic, and electronic structure studies of Mg0.95Mn0.05Fe2−2xTi2xO4 ferrite using x-ray diffraction, dielectric spectroscopy, DC magnetization and near edge x-ray absorption fine structure (NEXAFS) measurements. The x-ray diffraction study shows a structural transition from cubic to tetragonal with Ti substitution. The dielectric constant and DC conductivity increase with Ti substitution up to x = 0.2. However, with further increase of substitution both the dielectric constant and DC conductivity decrease. This electrical behavior indicates that at low values of substitution, hopping between Fe3+ and Fe2+ increases whereas at higher concentrations the total content of Fe ions decreases. It is observed that all the samples exhibit ferrimagnetic behavior at 300 K and the saturation magnetization decreases with increase in Ti substitution. The NEXAFS measurements have been carried out at O K-, Fe L-, Fe K-, and Ti L-edges to investigate the chemical states and the electronic structure of the Mg0.95Mn0.05Fe2−2xTi2xO4 (0≤x≤0.5) system at room temperature. The O K-edge spectra indicate that the Fe 3d orbitals are considerably modified with the substitution of Ti ions. At x≥0.3, a new spectral feature appears (~532 eV) due to the transitions from oxygen 2p to Ti 3d orbitals which starts dominating the pre-edge spectra of the system. Both Fe L3,2- and Fe K-edge spectra indicate that iron Fe3+ ions convert into Fe2+ with the substitution of Ti ions. The Ti L3,2-edge NEXAFS spectra reveal that the Ti remains in the 4+ state for all the samples. The observed experimental results have been explained on the basis of dilution of the magnetic sublattice by Ti substitution, which provides a strong interplay between electrical and magnetic properties along with their electronic structure.

Ferromagnetic Property of Co and Fe-Implanted ZnO Thin Film at Room Temperature

The results Co and Fe implanted ZnO thin films were studied before and after 200 MeV Ag ion irradiation. The as-implanted films shows the presence of nano sized Co and Fe clusters as seen through XRD patterns and exhibited high resistivity compared to un-implanted films. After Ag ion irradiation the Co and Fe clusters get dissolved in ZnO lattice and the films resistivity reduced to half of the as implanted values. The magnetic properties of Ag irradiated films were confirmed through magnetization hysteresis and Co implanted films exhibit higher magnetization compared to Fe implanted films.

Solubility of Co clusters in Co-implanted ZnO thin films by 200 MeV Ag15+ ions irradiation

We have investigated the structural, electrical resistivity, pink noise (1/f noise) and magnetic properties of 200 MeV Ag15+ ions (fluence ~1 × 1012 ions cm−2) irradiated Co-implanted ZnO thin films. The ZnO films were grown on Al2O3 substrate by the PA-MBE technique and 80 keV Co ion implantation with 1 × 1016 ions cm−2 dose value. The structural studies of an unirradiated film show the presence of Co clusters, which dissolve in the ZnO matrix on swift heavy ion (SHI) irradiation. The temperature-dependent electrical resistivity plots of pristine (unirradiated) and irradiated films demonstrated semiconducting nature. The resistivity data were fitted in the Motts variable range hopping (VRH) model and the activation energies were estimated. The magnitude of normalized noise SV/V2 increases with decrease in temperature and estimated Hooges parameters have higher values as compared to other semiconductors. We observe a clear magnetic hysteresis loop with coercivity ~65 Oe for both the films at room temperature, establishing the ferromagnetic nature. The correlation between the electrical transport and magnetic properties in the present system formulates it to be a potential aspirant for the spintronics-oriented devices.

Formation and Interface Analysis of Ti ∕ Ni ∕ Ti ∕ Au Ohmic Contacts on n -Type 6H–SiC

We present the results of TiNiTiAu multilayer ohmic contacts on n -type 6H-SiC and their interface analysis. The as-deposited contacts show rectifying behavior and, with the increase in annealing temperature, they gradually transform to high-quality ohmic contacts exhibiting linear current-voltage characteristics. The interface evolution was analyzed through glancing angle X-ray diffraction, Auger electron spectroscopy, and atomic force microscopy. The Ti Si2 and Ni2 Si formed at the interfaces during the low-temperature annealing initiate the conversion from Schottky to ohmic behavior, while the increased Ni2 Si formation at high-temperature annealing makes the perfect ohmic contacts. The results were interpreted through the thermodynamic reaction mechanisms. © 2007 The Electrochemical Society.