R. Srivastava

Optical Absorption Study of Molybdenum Diselenide and Polyaniline and their Use in Hybrid Solar Cells

The optical characterization of Molybdenum diselenide (MoSe2) and polyaniline (PANI) has been carried in the wavelength range 200 nm to 2500 nm. The detailed analysis of the optical properties has been carried out only for a range 200 nm to 800 nm from which the indirect band gap around 1.42 eV for MoSe2 and 1 eV and 2.5 eV for PANI was evaluated. It was interesting to note that π π* transitions lead to two distinct orders of energy gaps. The hybrid cells were fabricated using a photosensitive interface between MoSe2 and PANI. Various parameters of these heterostructure hybrid cells have been evaluated and it was found that the photoconversion efficiency was around 1%. Using the solar cell characteristics, the presence of trapping centers at the n-MoSe2/ p-PANI interface has been confirmed.

Structural and Thermoelectric Properties of Tungsten Diselenide Crystals

Crystals of Tungsten diselenide (WSe2) have been grown by direct vapour transport (DVT) technique using micro processor controlled dual zone horizontal furnace. The chemical composition and structure of grown crystals were confirmed using energy dispersive analysis of X‐ray (EDAX) and X‐ray diffraction (XRD). In the present investigation thermoelectric power measurements (TEP) have been carried out on the grown crystals. Different electrical transport parameters of semiconductors have been determined and discussed in the paper.Crystals of Tungsten diselenide (WSe2) have been grown by direct vapour transport (DVT) technique using micro processor controlled dual zone horizontal furnace. The chemical composition and structure of grown crystals were confirmed using energy dispersive analysis of X‐ray (EDAX) and X‐ray diffraction (XRD). In the present investigation thermoelectric power measurements (TEP) have been carried out on the grown crystals. Different electrical transport parameters of semiconductors have been determined and discussed in the paper.

Surface Studies of PVT Grown CdS Crystals

Physical vapour technique (PVT) is a versatile method to grow IIVI semiconductors. In present investigations, CdS crystals have been grown by this method using dual zone micro processor controlled horizontal furnace. CdS crystals grown in present case have been characterized by EDAX for stoichiometric conformation. The roughness of surface of grown CdS crystals has been studied in detail using optical microscopy, SEM and AFM. The surface topography study of as grown crystals has been carried out to understand the growth mechanism which was necessary for its application in electronic devices.

Thickness Dependent Structural and Optical Properties of Cadmium Selenide Thin Films

In this paper structural and optical properties of CdSe thin films with different thickness deposited by thermal evaporation under vacuum onto glass substrates are presented. The structural investigations performed by means of XRD technique showed that the films have a polycrystalline and hexagonal (würtzite) structure. The values of some important parameters of the studied films (absorption coefficient and optical bandgap energy) are determined from transmission spectra. The values of the optical bandgap energy (Eg) calculated from the absorption spectra, ranged between 1.67 - 1.74 eV.

Preparation and Characterization of N-CdS Thin Films and its Schottky Barrier

Cadmium sulphide (CdS), a member of group II-VI semiconductors is one of the promising materials from its applications point of view. The present investigations are about the preparation, structural and optical characterization of CdS thin films and their use as Schottky diode with Aluminum. Thin films of CdS having thickness around 700nm have been deposited by thermal evaporation. The chemical composition of the deposited CdS thin films has been made using EDAX technique. The structural characterization of this films was carried out using XRD. The structure of CdS after the deposition was found to be Cubic. Also, the lattice parameters were evaluated from the XRD data. From TEM of CdS thin films, the polycrystalline nature was confirmed. Optical characterization has been carried out using UV-VIS-IR spectroscopy. The direct as well as indirect band gaps obtained are 1.64eV and 1.48eV respectively. Schottky junctions were formed by a thermal vapor-deposition of 500nm Al films on pre-coated CdS glass substrates. Diode parameters, such as the zero bias barrier height φb0, the flat band barrier height φbf and the ideality factorη, were calculated using thermionic emission theory at room temperature.

Structural and Optical Properties of e‐Beam Evaporated MX2 Thin Films

WSe2 and MoSe2 thin films were obtained by using electron beam evaporation technique at room temperature. The films were characterized by EDAX, XRD, TEM and optical absorption. The X‐ray diffraction pattern shows that prepared polycrystalline thin films have a hexagonal phase which is confirmed by TEM also. Optical properties show a direct bandgap with bandgap energy 1.89 eV and 1.98 eV for WSe2 and MoSe2 respectively.

Optical Absorption in Mo0.25W0.75Se2 Single Crystals

Single crystals of Mo0.25W0.75Se2 have been grown by direct vapour transport technique. Optical absorption spectra have been measured in the range 200–2000 nm at room temperature. Results have been analyzed on the basis of three dimensional (3D). Absorption near the fundamental edge was found to be due to indirect and direct allowed transitions on the basis of 3D model. The optical energy gaps corresponding to both transitions have also been determined. Some feeble disorder in the crystal is conceived to be present.