Yasube Kashiwaba

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.

Characterization of spray pyrolysed indium sulfide thin films

Indium sulfide thin films have been prepared using the chemical spray pyrolysis technique. Samples with different substrate temperatures and indium-to-sulfur (In/S) ratios have been prepared and characterized using x-ray diffraction (XRD), x-ray photoelectron spectroscopy, photosensitivity measurements and optical absorption studies. XRD studies have revealed that the samples are β-In2S3. The optical bandgap has been found to decrease from 2.81 to 2.64 eV with the In/S ratio varying from 2/1 to 2/8. The photoresponse of the samples can be improved by changing either the In/S ratio in the solution or the substrate temperature. From this study we observe that, in terms of crystallinity, bandgap and photoresponse, the sample with the In/S ratio of 1.2/8 is very suitable for any photovoltaic application.

Schottky ultraviolet photodiode using a ZnO hydrothermally grown single crystal substrate

A Schottky ultraviolet photodiode using a (0001) ZnO single crystal grown by the hydrothermal growth method is reported. The photodiode consisted of a semitransparent Pt film for the Schottky electrode and an Al thin film for the Ohmic electrode. The photodiode had polarity dependences on current-voltage characteristics and on responsivity. In the case of the Schottky electrode on the zinc surface, the responsivity was 0.185A∕W at a wavelength of 365nm. On the other hand, the responsivity was 0.09A∕W for an oxygen surface. The results are attributed to the polarity dependences of surface chemical reactivity and the surface state density on ZnO surfaces.

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.

Chemical bath deposition of different phases of copper selenide thin films by controlling bath parameters

Abstract In the preparation of copper selenide thin films using chemical bath deposition (CBD) technique, it is observed that the pH of the final reacting mixture is the major factor controlling the composition of the film. Thin films of cubic Cu2−xSe and tetragonal Cu3Se2, of band gaps 2.20 and 2.83 eV, respectively, have been prepared using the CBD technique by adjusting the bath parameters like pH, temperature and the ratio between copper and selenium atoms in the reaction bath. X-ray diffraction analysis is used as the major tool for identification of these phases. The results have been confirmed using XPS, ICP and absorption studies.

Reversible Cu2−xSe↔Cu3Se2 phase transformation in copper selenide thin films prepared by chemical bath deposition

Abstract This paper reports the inter phase conversion of Cu 2− x Se and Cu 3 Se 2 thin films prepared using the chemical bath deposition (CBD) technique. Chemically prepared Cu 2− x Se phase is found to be less stable than the Cu 3 Se 2 phase in ambient conditions. With aging the Cu 2− x Se phase gets converted to the Cu 3 Se 2 phase along with the formation of copper oxide impurity. The Cu 3 Se 2 phase is stable in ambient conditions but is unstable at temperatures above 140°C where it reverts to the Cu 2− x Se phase. This inter phase conversion is found to be cyclic. The relative stability of these phases is studied in detail with the help of X-ray diffraction, optical absorption and X-ray photoelectron spectroscopy.

Defect analysis of sprayed β-In2S3 thin films using photoluminescence studies

In this paper we report for the first time the results of photoluminescence (PL) studies on thin films of a β-In2S3 compound semiconductor, grown using a chemical spray pyrolysis (CSP) technique. PL emission in the wavelength range 550–900 nm was recorded using a 488 nm line from a Ar+ laser as the excitation source. There were two PL bands, centred at 568 nm (band A) and 663 nm (band B). A shift in the PL peak energy and full width at half maximum of the former band due to a variation in temperature strongly suggested that the emission followed the Cartesian coordinate (CC) model of luminescence, while the latter was found to have arisen from transitions between a donor–acceptor pair. Band A was most dominant in the sulfur-deficient sample and hence associated with a sulfur vacancy, while band B was dominant in the indium-rich sample and hence linked with indium interstitials. The proposed energy level scheme allowed us to interpret the recombination processes in β-In2S3 thin films.

CuInSe2 thin film preparation through a new selenisation process using chemical bath deposited selenium

Copper indium selenide thin films were prepared through a novel and an eco-friendly selenisation process. In this method, selenium film required for selenisation was prepared using chemical bath deposition technique, at room temperature. Thus, totally avoided usage of highly toxic H2Se or selenium vapour. Here, the process involved annealing the Stacked layer, Se/In/Cu in which Cu and In were deposited using vacuum evaporation technique. Investigations on the solid-state reaction between the layers were done by analysing structural and optical properties of films formed at different annealing temperatures. Optimum annealing condition for the formation of copper indium selenide thin film was found to be 673 K for 1 h in high vacuum. Compositional dependence of the growth process was also studied using various Cu/In ratios. Optical band gap was decreased with increase in Cu/In ratio. Carrier concentration and hence conductivity were found to be increased with increase in Cu/In ratio. The films obtained were p-type and highly Cu-rich films were degenerate.

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...

Preparation of CuInS2 thin films using CBD CuxS films

This paper reports the conversion of CBD CuxS films into CuInS2 films. XRD spectra of the as-prepared CuxS films show lack of crystallinity. When pure indium is evaporated over these films and the samples are subsequently annealed, the film improves in crystallinity and shows major peaks of CuInS2. Absorption spectra and XPS depth profile of the samples support this result.