Tanveer A. Dar

Type I and type II band alignments in ZnO/MgZnO bilayer films

We report the change in the type of band alignments due to an increase in the dopant (Mg) concentration in pulsed laser deposited ZnO/MgZnO bilayer film. The band offset measurements were carried out from the core level shifts as well as valence band maxima in the single as well as the bilayer films. The change in the type of band alignment is attributed to the surface enrichment of Mg at the heterojunction.

Transport and magnetotransport study of Mg doped ZnO thin films

We report negative magnetoresistance in pulsed laser deposited single phase ZnO and Mg0.268Zn0.732O films and attribute it to the presence of oxygen interstitials (Oi) and zinc interstitials (Zni) as observed in the X-ray photoelectron spectra of the films. An interesting feature of reduction of negative magnetoresistance at low temperatures and large fields in Mg0.268Zn0.732O film is observed and is explained by taking into account the localized scattering.

Insight into the effect of screw dislocations and oxygen vacancy defects on the optical nonlinear refraction response in chemically grown ZnO/Al2O3 films

We report the effect of screw dislocations and oxygen vacancy defects on the optical nonlinear refraction response of ZnO films grown on a sapphire substrate at various oxygen flow rates using the chemical vapor deposition technique. The nonlinear refraction response was investigated in the off-resonant regime using a CW He-Ne laser source to examine the role of the intermediate bandgap states. It has been observed that the structural defects strongly influence the optical nonlinearity in the off-resonant regime. Nonlinearity has been found to improve as the oxygen flow rate is lowered from 2 sccm to 0.3 sccm. From photoluminescence studies, we observe that the enhanced defect density of the electronic defect levels due to the increased concentration of structural defects (with the decrease in the oxygen flow rate) is responsible for this improved optical nonlinearity along with the thermal effect. This suggests that defect engineering is an effective way to tailor the nonlinearity of ZnO films and their utility for optoelectronic device applications.We report the effect of screw dislocations and oxygen vacancy defects on the optical nonlinear refraction response of ZnO films grown on a sapphire substrate at various oxygen flow rates using the chemical vapor deposition technique. The nonlinear refraction response was investigated in the off-resonant regime using a CW He-Ne laser source to examine the role of the intermediate bandgap states. It has been observed that the structural defects strongly influence the optical nonlinearity in the off-resonant regime. Nonlinearity has been found to improve as the oxygen flow rate is lowered from 2 sccm to 0.3 sccm. From photoluminescence studies, we observe that the enhanced defect density of the electronic defect levels due to the increased concentration of structural defects (with the decrease in the oxygen flow rate) is responsible for this improved optical nonlinearity along with the thermal effect. This suggests that defect engineering is an effective way to tailor the nonlinearity of ZnO films and their ...

Negative thermo-optic coefficients and optical limiting response in pulsed laser deposited Mg-doped ZnO thin films

Thermo-optic properties and optical limiting characteristics are investigated in pulsed laser deposited Mg-doped ZnO thin films by performing a Z-scan experiment in the off-resonant regime using a CW He–Ne laser source. Optical limiting studies in these thin films lead to a conclusion that reverse saturable absorption is the major mechanism for optical limiting properties in these films and nonlinear refraction is caused due to the thermal lensing effect. Negative thermo-optic coefficients were observed, indicating potentiality for athermalization, required to counter the effect of thermal expansion. Sufficiently large thermo-optic coefficients and good optical limiting response suggest the utility of MgZnO films for thermo-optic switches and optical limiting device applications.

Role of Ni doping on transport properties of ZnO thin films

Nickel doped (Ni=0.05) and undoped Zinc Oxide (ZnO) thin films have been prepared by Pulsed laser deposition (PLD) technique. The structural analysis of the films was done by X-ray diffraction (XRD) studies which reveal absence of any secondary phase in the prepared samples. UV transmission spectra show that Ni doping reduces the transparency of the films. X-ray Photoelectron spectroscopy (XPS) also shows the presence of metallic Ni along with +2 oxidation state in the sample. Low temperature magneto transport properties of the ZnO and NiZnO films are also discussed in view of Khosla fisher model. Ni doping in ZnO results in decrease in magnitude of negative MR.

Effect of annealing on the optical properties of the ion beam sputtered NiO thin film

Effect of annealing on optical characteristics of Nickel oxide thin films deposited by ion beam sputtering technique from a Ni target in a mixture of oxygen and argon gas on to a glass substrate has been studied. The deposited films were characterized in as deposited state(S1) and after annealing(S2) at temp of 523 K. Crystalline properties of films were investigated using X-ray diffraction technique from which we found that both S1 and S2 shows the polycrystalline nature with preferential growth along (111) plane. The transmittance of the S2 films was decreased. The surface morphology of the film was studied using atomic force microscopy (AFM). The nonlinear optical properties of the films were obtained using z-scan technique which reveals that the nonlinear absorption coefficient of S2 films is larger than that of S1 samples. Improved nonlinearity suggests the utility of the grown films for optoelectronic device application.

Nonlinear absorption coefficient of pulsed laser deposited MgZnO thin film

We report the imaginary part of 3rd order nonlinear susceptibility and the nonlinear absorption coefficient of Mg doped ZnO thin film using standard Z-scan technique. The origin of nonlinear absorption is attributed to the two photon absorption followed by the free carrier absorption because of the presence of oxygen vacancy defects. We have also confirmed the experimental results with the theoretical results obtained by considering the steady state response of a two level atom with the monochromatic field models.