R. Sathyamoorthy

Implantation-assisted Co-doped CdS thin films: Structural, optical, and vibrational properties

This paper reports on structural, optical, vibrational, and morphological properties of cobalt-doped CdS thin films, prepared by 90 keV Co+ implantation at room temperature. In this work, we have used cobalt concentration in the range of 0.34–10.8 at. %. Cobalt doping does not lead to the formation of any secondary phase, either in the form of metallic clusters or impurity complexes. However, with increasing cobalt concentration a decrease in the optical band gap, from 2.39 to 2.26 eV, is observed. This reduction is addressed on the basis of band tailing due to the creation of localized energy states in association with Urbach energy calculations. In addition, implantation gives rise to grain growth and increase in the surface roughness. Size and shape fluctuations of individual CdS grains, at higher fluences, give rise to inhomogeneity in strain. The results are discussed in the light of ion-matter interaction in the keV regime.

Structural and optical properties of Mn-doped CdS thin films prepared by ion implantation

We report on structural and optical properties of Mn-doped CdS thin films prepared by 190 keV Mn-ion implantation at different temperatures. Mn-ion implantation in the fluence range of 1×1013–1×1016 ions cm−2 does not lead to the formation of any secondary phase. However, it induces structural disorder, causing a decrease in the optical band gap. This is addressed on the basis of band tailing due to creation of localized energy states and Urbach energy calculations. Mn-doped samples exhibit a new band in their photoluminescence spectra at 2.22 eV, which originates from the d-d (T41→A61) transition of tetrahedrally coordinated Mn2+ ions.

Dielectric and ac conduction properties of zinc phthalocyanine (ZnPc) thin films

The dielectric responses of zinc phthalocyanine (ZnPc) thin films, deposited using the vacuum evaporation technique, were studied as functions of frequency and temperature. The conductivity of the deposited films decreases with increase in temperature. The dielectric studies clearly indicated that the Debye type of polarization exists in these films. The relaxation phenomena have been confirmed from the Cole-Cole plot. The relaxation times have been evaluated from the plot and were found to be (τa) 0.0137 and 0.0106s at 303 and 403K, respectively. The prevailing conduction mechanism in ZnPc films, under an ac field, was found to be electronic hopping. The activation energy was evaluated from the Arrhenius plot and was found to be 1.28eV. Based on the structure, and with the help of quantum mechanics calculations, the electronic structure and behavior that upheld our experimental results were identified.

Effect of substrate temperature on implantation doping of Co in CdS nanocrystalline thin films

We demonstrate doping of nanocrystalline CdS thin films with Co ions by ion implantation at an elevated temperature of 573 K. The modifications caused in structural and optical properties of these films are investigated. Co-doping does not lead to amorphization or formation of any secondary phase precipitate for dopant concentrations in the range of 0.34-10.8 at.% used in the present study. However, we observe a systematic reduction in the d-spacing with increasing cobalt concentration. Optical band gap of CdS does not show any obvious change upon Co-doping. In addition, implantation gives rise to grain growth and increase in the surface roughness. The results are discussed in the light of ion-matter interaction in the keV regime.

Schottky nature of InSe/Cu thin film diode prepared by sequential thermal evaporation

Highly oriented indium selenide (InSe) thin films were prepared by sequential thermal evaporation on tungsten (W) substrate and subsequently annealed at 300°C for 30 min in argon (Ar) atmosphere. The films were characterized by Glancing Incidence x-ray diffraction (GI-XRD), scanning electron microscopy (SEM), Energy dispersive x-ray analysis (EDX), Diffused reflectance spectroscopy (DRS) and current-voltage (I–V) measurements. Highly crystalline InSe thin film was obtained after annealing and confirmed by XRD analysis. Band gap energy of the InSe system is deduced from the DRS measurements and found to be 1.3 eV. SEM analysis revealed that selenium (Se) content plays an important role in determining the surface morphology of the film. InSe thin film diode structure was fabricated as W/InSe/Cu system. The estimated values of barrier height for the film of thickness 3000 Å and 7000 Å are 0.65 eV and 0.61 eV respectively. Thickness dependent schottky nature of the InSe/Cu thin film diode is discussed in detail.

Evidence for phase change memory behavior in In2(SexTe1−x)3 thin films

Crystalline In2(Se0.5Te0.5)3 thin films are prepared by thermal evaporation and subsequently annealed at 300°C in Ar atmosphere. SEM image of the crystalline sample shows spherical nature of constituents, distributed uniformly throughout the surface. Island structure of the surface is clearly visible after switching. Elemental composition of the sample remains unchanged even after switching. Temperature dependent I-V analysis shows stoichiometric phase change at 80°C [from In2(Se0.5Te0.5)3 to In2Te3 and In2Se3 phase], where current switches three orders of magnitude higher than that in lower temperature. Further rise in temperature results increase in current only after switching, where threshold voltage remains constant.

Structural and morphological properties of Ag ion irradiated SnO2 thin films

SnO2 thin films of thickness 300 nm were prepared by reactive thermal evaporation and subjected to sintering at 600 °C for 2 hr. The annealed films were irradiated using silver (Ag) ions with energy of 120 MeV at different fluences (1×1011, 5×1011, 1×1012, 5×1012 and 1×1013 ions/cm2). The effect of swift heavy ion (SHI) irradiation on structural, morphological and optical properties were studied using X-ray diffractometer (XRD), Scanning electron microscopy (SEM) and UV-visible spectrophotometer. XRD studies showed formation of tin oxide with tetragonal structure. Morphology analysis revealed uniform deposition of the material with increase in grain size after irradiation upto 1×1012 ions/cm2 and beyond that size tends to decrease. In addition, agglomeration of nanocrystalline grains was observed after Ag ion bombardment with varying fluence. The transmittance decreases from 90% to 80% as the fluence increases.

Structural and optical properties of thermally evaporated antimony telluride thin films

Antimony telluride thin films were prepared on the well-cleaned glass substrates under a pressure of 10 – 5 torr by thermal evaporation method. The thicknesses of the films were measured using Multiple Beam Interferometer (MBI) technique. The structure of the sample was analyzed by X-ray diffraction technique. The film attains crystalline structure as the temperature of the substrate is increased to 373 K. The d spacing and the lattice parameters of the sample were calculated. Optical behavior of the film samples with the various thicknesses was analyzed by obtaining their transmittance spectra in the wavelength range of 400 – 800 nm. The transmittance is found to decrease with increase in film thickness and also it falls steeply with decreasing wavelength. The optical constants were estimated and the results are discussed. The optical band gap energy decreases with increase in the film thickness. The optical transition in these films is found to be indirect and allowed.

Synthesis of α-In 2 Te 3 thin films from In/Te bilayer by Si ion irradiation

In this work, In/Te bilayer thin films were prepared using sequential thermal evaporation method and subsequently irradiated using swift heavy ions (SHIs) of 100 MeV silicon (Si) with different fluences (1×1013 to 5×1013/cm2). The inter-diffusion of In and Te layers was highly controlled by SHI irradiation and the In2Te3 formation capability was compared with that of the conventional annealing method. The structural as well as optical properties of a post-sintered SHI-irradiated In/Te bilayer were investigated using X-ray diffraction (XRD) measurements and UV–visible spectroscopy, respectively. We found that irradiated samples showed single-phase In2Te3 under post-annealed conditions at 150 °C unlike that prepared using the conventional thermal annealing method, which showed mixed phases under similar conditions. This confirms the effective inter-diffusion in bilayer films by SHI irradiation toward the formation of single-phase In2Te3. The estimated optical band gap energy was found to be 1.1±0.5 eV and strongly corroborated the XRD results. In addition, the estimated refractive index (n) value of the SHI-irradiated sample (∼3.3) was higher than that of the sample obtained through the conventional annealing method (∼2.8). This proves that SHI offers a highly compact nature even at low temperatures. This work has a wide scope for achieving single-phase alloyed films through bilayer mixing by SHI irradiation.