P. M. Ratheesh Kumar

On the properties of indium doped ZnO thin films

Thin films of undoped and In-doped zinc oxide, prepared using chemical spray pyrolysis, were investigated using x-ray diffraction, optical transmission and absorption spectra, SEM, resistivity measurements, x-ray photoelectron spectroscopy and photoluminescence studies. A doping level of 1 at% indium was found to give lowest resistive films and enhanced optical transmission. But increasing the doping percentage resulted in lower optical transmission. XPS investigations revealed the presence of elemental chlorine in the In-doped film. Undoped ZnO thin films gave a strong blue-green emission. Doping with indium apparently resulted in a competitive phenomenon that overshadows the blue-green emission and gave rise to three emissions at 408, 590 and 688 nm.

Modifications of ZnO thin films under dense electronic excitation

Spray pyrolyzed ZnO films prepared using solution containing ethanol and water (volume ratio 1:1), exhibited optical transmission of 85% in the visible range and electrical resistivity of 78Ωcm. These samples were irradiated using 120MeV Au ion beam and then characterized using optical absorption and transmission, x-ray diffraction (XRD), electrical resistivity measurements, x-ray photoelectron spectroscopy (XPS), and photoluminescence studies. It appears that irradiation does not affect absorption edge while optical transmittance was slightly reduced. But intensities of peaks of XRD and photoluminescence were found to decrease continuously with increasing ion fluence. Electrical resistivity of the films decreased considerably (from 78to0.71Ωcm) with increase in ion fluence. Atomic concentration from XPS analysis showed that Zn∕O ratio is getting increased due to ion beam irradiation. Variations in carrier concentration were also measured using Hall measurements.

Doping of spray-pyrolyzed ZnO thin films through direct diffusion of indium: Structural optical and electrical studies

Effect of thermal diffusion of indium in ZnO thin films, prepared using spray pyrolysis technique, is discussed. ZnO:In films were characterized using different techniques such as x-ray diffraction (XRD), photoluminescence, electrical resistivity measurements, and optical absorption and transmission. The XRD analysis showed that all the films had a preferred (002) orientation. There was no considerable change in peak height or full width at half maximum, due to the variation in doping percentage. Peak positions corresponding to (002) and (101) planes were slightly shifted to lower 2θ values. Optical band gap also decreased slightly with indium concentration, and for higher indium concentration percentage of transmission reduced very much. Drastic decrease in resistivity was observed and two activation energies (30 and 15meV) were obtained for the doped samples. These levels were identified as due to zinc interstitials and/or due to indium at zinc lattice and impurity related defect levels. Photoluminescen...

Anomalous behavior of silver doped indium sulfide thin films

The effect of doping spray pyrolyzed thin films of In2S3 with silver is discussed. It was observed that silver diffused into In2S3 films in as deposited condition itself. Depth profile using x-ray photoelectron spectroscopy clearly showed diffusion of silver into In2S3 layer without any annealing. X-ray analysis revealed significant enhancement in crystallinity and grain size up to an optimum percentage of doping concentration. This optimum value showed dependence on thickness and atomic ratio of indium and sulfur in the film. Band gap decreased up to the optimum value of doping and thereafter it increased. Electrical studies showed a drastic decrease in resistivity from 1.2×103to0.06Ωcm due to doping. A sample having optimum doping was found to be more photosensitive and low resistive when compared with a pristine sample. Improvement in crystallinity, conductivity, and photosensitivity due to doping of spray pyrolyzed In2S3 films with Ag helped to attain efficiency of 9.5% for Ag∕In2S3∕CuInS2∕ITO (indium...

Swift heavy ion-induced interface mixing in In/Sb

In/Sb is integrated with Si by a process of high energy heavy ion beam mixing. The samples of In/Sb deposited on the Si substrate were irradiated using 100 MeV Au ions having fluences from 1 × 1012 to 6 × 1013 ions cm−2. Phase formation due to ion beam mixing was detected using high-resolution x-ray diffraction measurements. X-ray photoelectron spectroscopy measurements indicated that both In and Sb were embedded in the Si substrate with an irradiation dose of 3 × 1013 ions cm−2. Formation of InSb phase was observed in the irradiated sample, at a fluence of 1 × 1013 ions cm−2 and higher, without any post-irradiation annealing.

An investigation on the variations in properties of Ni+ irradiated ZnO thin films

ZnO thin films, irradiated by 80 MeV Ni+ ions, were analysed with the help of different characterization techniques like X-ray diffraction, optical absorption, transmission, photoluminescence (PL), electrical resistivity, photosensitivity (PS) and thermally stimulated current (TSC) measurements. Crystallinity and absorption edge were hardly affected by irradiation. PL spectrum of pristine sample showed a broad peak at 517 nm, whereas irradiated film had two emissions at 517 and 590 nm. Intensity ratio between these two emissions (I517/I590) decreased with the fluence, and finally at a fluence of 3×1013 ions/cm2, the emission at 517 nm completely disappeared. Electrical resistivity of the sample irradiated with a fluence of 1×1013 ions/cm2 drastically increased. However, on increasing the fluence to 3×1013 ions/cm2, resistivity decreased, probably due the onset of hopping conduction through defects. PS also decreased due to irradiation. TSC measurements on pristine sample could reveal only one defect level at 0.6 eV, due to interstitia1 zinc (ZnI). But, irradiation at a fluence of 1×1012 ions/cm2, resulted in three different defect levels as per TSC studies. Interestingly, the sample irradiated at a fluence of 3×1013 ions/cm2 had only one defect level corresponding to a deep donor. The possible origin of these defect levels is also discussed in the paper.

Surface topology using laser backscattering and photoluminescence on Cu- and In-rich CuInSe2 thin films

An easy-to-arrange imaging system was fabricated and used to probe surface topology of polycrystalline CuInSe2 thin films used for solar cell fabrication. Surface images developed using laser backscattering and photoluminescence (PL) showed correlation with AFM images. Imaging by laser backscattering was faster compared to PL imaging. The backscattered image was a profile of the air–film interface, which represented more closely the topology obtained using atomic force microscopy (AFM) analysis. Surface roughness calculated using laser backscattering was found to be agreeable with the value obtained using a stylus probe. PL topology was of lower resolution probably because of the infrared emission wavelength used for the imaging. Cu-rich films possessed hills and valleys on their surfaces while In-rich films were smoother with rounded features. The spatial distribution of PL intensity was correlated with the spatial defect distribution.