Sindhu Singh

Electrodeposited semiconducting CuInSe2 films. I. Preparation, structural and electrical characterisation

Ternary compound semiconductor CuInSe2 film has been deposited cathodically under galvanostatic conditions from an aqueous solution containing CuCl2, InCl3 and SeO2. The deposition parameters have been optimised for electrodeposition of CuInSe2. Structural characterisation of the deposited film has been carried out using EDAX and EM studies. Optical absorption study shows that the band gap of the deposited material is 1.08 eV. The resistivity and trap density of the electrodeposited film are respectively approximately 103 ohm cm and approximately 1014 cm-3 as determined by I-V characteristics.

Electronic Structure, Electrical and Dielectric Properties of BaSnO3 below 300 K

The electronic structure, electrical and dielectric properties of barium stannate, a semiconducting perovskite oxide prepared by solid state ceramic route were studied by employing X-ray photoelectron spectroscopy (XPS), Mossbauer and impedance spectroscopic techniques in the temperature range 77–300 K. X-ray diffraction (XRD) pattern of BaSnO3 confirms the cubic structure. Scanning electron microscopy (SEM) images show high porosity in the sample and the average grain size was found to be about 1.85 µm which corroborates with the particle size obtained through XRD line broadening analysis. Mossbauer spectra, at 298 and 78 K reveal that tin exists mainly in tetravalent, Sn4+ state. XPS study also shows the same results but it indicates the existence of a trace amount of Sn2+. Electrical conductivity and dielectric constant of this system have been measured in the temperature range 298 to 148 K and in the frequency range 10-2 to 106 Hz. Frequency and temperature dependent electrical conductivity/dielectric properties have been used to separate the contributions of grains and grain boundaries to the total observed conductivity and dielectric constant. Orientational polarisation and space charge polarisation contributes to the observed dielectric properties of the system.

Alumina nanoparticles find an application to reduce the ionic effects of ferroelectric liquid crystal

We observed that the doping of alumina nanoparticles (AL-NPs) has suppressed the undesired ionic effect in ferroelectric liquid crystals (FLCs). The pure and AL-NPs doped FLC cells were analysed by means of dielectric spectroscopy and electrical resistivity/conductivity measurements. Dielectric loss spectra confirmed the disappearance of the low-frequency relaxation peak, which appears due to the presence of ionic impurities in the FLC materials. The reduction of ionic effects has been attributed to the strong adsorption of ionic impurities on the surface of AL-NPs. The adsorption capability of AL-NPs has been studied with both the size and their concentration in FLC material. This study would be helpful to minimize the undesired ionic effects of LC-based display devices.

Electrical behaviour of zirconium doped calcium copper titanium oxide

In this investigation, the effect of Zr substitution at the Ti site of the CaCu3Ti4O12 on the electrical properties has been studied. Samples with composition x = 0.00, 0.10 and 0.30 have been synthesized by the solid state ceramic route in the system CaCu3Ti4−xZrxO12. Powder x-ray diffraction data showed the formation of a single phase solid solution. The structure remains cubic similar to an undoped sample. The Seebeck coefficient, α, is measured on a thick pellet in the temperature range 500–800 K and is found to be negative in this temperature range, indicating n-type conduction in the temperature range of measurement. Dc resistivity, ρdc, and ac conductivity, σac, were measured to understand the mechanism of conduction. Immittance analysis is used to separate the contributions of the grains and grain boundaries to the total observed resistance. From the temperature and frequency dependence of ac conductivity, it is concluded that at and around room temperature conduction occurs due to thermally activated rotation of dipoles while at high temperature it occurs due to excitation of charge carriers at the conduction band edge and hopping at energies close to it. From the immittance analysis it is observed that activation energies of conduction for grains and grain boundaries are almost equal indicating the same mechanism of conduction.

Electrodeposited semiconducting CuInSe2 films. II: Photo-electrochemical solar cells

For pt.I see ibid., vol.19, p.1299 (1986). Electrochemical studies (Mott-Schottky plot and J-V characteristics) of an electrodeposited CuInSe2 film in contact with aqueous S2-/S22- redox electrolyte have been carried out. The material is n-type and the charge transfer at the interface occurs via the valence band involving the surface states and deep traps also. The values of Vfb, ND, W, Ec and Ev have been evaluated. Photo-electrochemical solar cells have been fabricated using the above junction and studied for films with different stoichiometry.