K.P. Adhi

Structural, morphological, and electrical characterization of heteroepitaxial ZnO thin films deposited on Si (100) by pulsed laser deposition : Effect of annealing (800 °C) in air

Pulsed laser deposition technique was used for growing thin films of ZnO on Si (100) substrate held at different temperatures (Ts). All the as-deposited films have shown a preferential c-axis orientation associated with varying grain size as a function of Ts ranging from 100to600°C. Current-voltage (I-V) characteristics of these films show Ohmic behavior over the entire Ts range studied. These films were subjected to annealing at 800°C in air ambient for 4h. The grain size was observed to increase after the annealing process for all the films deposited at different Ts. Interestingly, these annealed films show nonlinear variation of current with applied voltage, very similar to the one observed in doped ZnO varistors. The nonlinear parameters such as the asymmetric behavior of change in current on the polarity reversal of voltage, the plateau region, and the break down voltage are observed to depend on Ts. This nonlinear behavior can perhaps be explained on the basis of electronic conduction model proposed...

Effect of aluminum doping on the magneto-transport properties of La0.75Ca0.25MnO3

Abstract The influence of aluminum doping at Mn-site in La0.75Ca0.25MnO3 has been investigated, in the light of magnetotransport, and structural properties. As the aluminum concentration increases, the metal–insulator transition temperature (TP) decreases while activation energy in the insulating region (T>TP), resistivity and maximum value of magnetoresistance (MR) increases. The unit cell volume decreases slightly as the aluminum concentration increases. The observed results are analyzed in term of defect clustering due to aluminum doping at Mn-site induced random spin disorder and local strain and its effect on the magnetotransport properties.

Effect of 57Fe ion implantation on magnetotransport in epitaxial La0.67Ca0.33MnO3 thin films

Epitaxial thin films of La0.67Ca0.33MnO3 were implanted with 30 and 100 keV 57Fe ions at different fluence values to achieve a uniform implant distribution. The resistivity of the film increases as fluence increases, but the peak resistivity temperature Tp does not change significantly for the as-implanted sample. Annealing of the implanted samples at 950 °C allows recovery of the structural properties of the films and leads to interesting properties: increase of the peak resistivity and of the colossal magnetoresistance values, and decrease of Tp. The decrease in Tp is of ∼130 K, and the increase in resistivity is almost a factor of 28 as compared to the as-implanted sample.

Observation of electron tunneling induced photon emission in gallium (Ga) doped (1%) zinc oxide (ZnO) sample using scanning tunneling microscopy

Electron tunneling induced photon emission in gallium doped (1%) zinc oxide was detected by scanning tunneling microscope in ambient condition. Simultaneously acquired topography and photon maps reveal interesting correlation. Photon maps depict few intense emission spots. Existence of a threshold tunneling current (6 nA) and applied bias (1.8 V), for detectable photon emission was observed. Further analysis of the results suggests Fowler-type photon emission which is ascribed to radiative electron-hole recombination. Localized photon emission spectroscopy exhibits prominent peaks at hν=2.96, 3.43, and 3.80 eV, which match well with the results obtained from photoluminescence studies.

Electrical characterization of zinc oxide/aluminum nitride thin film precursor field effect transistor structures: A conducting atomic force microscopy and density functional theoretical study

Electrical transport across pulsed laser deposited zinc oxide (ZnO)/aluminum nitride (AlN)/Si(100) thin film structures has been studied using conducting atomic force microscopy. Current versus voltage spectroscopy performed on the samples with varying AlN layer thickness (t), revealed asymmetric nonlinear behavior with a finite zero current region. The effective barrier height of the system is found to be (∼0.2 eV). The width of the zero current region was found to decrease exponentially with respect to t finally attaining the bulk band gap value. Density functional theory based calculations were carried out on the AlN and AlN–ZnO composite surface to investigate the band gap variation and ZnO adsorption on AlN. Results obtained by these calculations are in harmony with the experimental findings. Calculated values of the bulk cohesive energy explain the growth of the ZnO in an axis perpendicular to the surface supporting the experimentally observed results. Constant voltage current scans studies on the s...

Direct observation/characterization of spatial distribution of current leakage spots in zinc oxide/aluminum nitride thin film precursor field effect transistor structures using conducting atomic force microscopy

Charge transport across pulsed laser deposited zinc oxide (ZnO)/aluminum nitride (AlN)/Si(100) thin film structures has been studied using conducting atomic force microscopy at different stages of sample preparation. The spatial coverage of current leakage spots could be directly imaged, characterized, and shown to exhibit hysteresis against applied bias voltage. Current-voltage (I-V) measurements on both AlN and ZnO/AlN/Si(100) structure exhibited asymmetric nonlinear behavior with a large zero current region. Further analysis of I-V and current-force data suggests Fowler–Nordheim like behavior under Hertzian contact as a dominant mechanism for electron transport.

Growth Kinetics Study of Pulsed Laser Deposited ZnO Thin Films on Si (100) Substrate

Surface morphology and kinetic roughness of ZnO thin films grown on Si(100) substrate for different time durations by pulsed laser deposition technique were analyzed using Atomic Force Microscopy images. Dynamic scaling approach was used for quantitatively analyzing the surface topology in terms of height difference correlation function G(rr, t) and interface width w(t). Dynamic scaling approach is used to find roughness exponent α and growth exponent β, which yields the values 0.67 and 0.49 respectively. This α value is in good agreement with the value predicted by surface diffusion driven model. However, value of growth exponent β is higher than the model value. The deviation suggests anisotropy in film growth. X‐ray diffraction data shows the preferential c‐axis growth supporting deviation from the diffusion driven model.