M. Nagabhushanam

Effect of copper doping on structural, optical and electrical properties of Cd0·8Zn0·2S films prepared by chemical bath deposition

Cd 0·8Zn 0·2S:Cu films of 1 ·3–6 ·1 mole percentage of copper have been grown on mica substrate by using chemical bath deposition technique. The films have been characterized by using XRD, SEM and UV spectrophotometer. X-ray diffraction studies have shown that the films are polycrystalline. The average crystallite size as measured from XRD data is in the range of 125–130 nm. The activation energies of Cd 0·8Zn 0·2S:Cu films, as observed from d.c. conductivity studies in the temperature range (77–300 K) studied, decreased with the increase in Cu concentration. The optical absorption studies have revealed that the energy gap increases gradually with an increase in Cu concentration, whereas conductivity studies have shown an anomalous increase in conductivity in films of 3 ·8 mole percentage of Cu. SEM pictures have revealed the presence of defects with spherical structure having fibre network. The variation of electrical conductivity is explained based on the defects present and by adopting tunneling mechanism.

Electrical and Thermoelectric properties of Cu doped Cd0.8Zn0.2S Compound prepared by modified Co-precipitation method

Cd0.8Zn0.2S compounds doped with different mol % of Cu (1.3, 2.5, 3.8, 5.0 and 6.1) have been prepared by modified chemical co-precipitation method (CCP method). Bulk Cd0.8Zn0.2S compounds have been prepared by adopting two different ways of mixing the solutions of constituent elements named as CCP-I & CCP-II. XRD studies have shown that the compounds grown by both methods are of polycrystalline nature. SEM micrographs have shown that the crystallites in CCP-I grown samples have needle like shape whereas the samples grown by CCP-II failed to show clear shape of the crystallites . The dc-electrical conductivity of all the samples grown by CCP-I & II are more than the undoped sample and the conductivity change in CCP-I samples is more than that of CCP-II samples. The variation in activation energy at low temperature region is more or less uniform than at high temperature region in CCP-II grown samples. TEP measurements have shown that all the samples have p-type semiconductor nature. Mobility of charge carrier was found to increase with the increase in temperature. This is governed by the scattering mechanism associated with inter-grain barrier height. It is observed In all the samples that the sum of the activation energy due to charge carriers and grain boundary potential is equal to the activation energy due to conductivity.

Structural and dc conductivity Studies of Cd0.8-x PbxZn0.2S Mixed Semiconductor Compounds

Cd0.8-xPbxZn0.2S ( x= 0-0.8 ) semiconductor powders have been prepared by controlled Co-precipitation Method in an alkaline medium using Thiourea as a sulphide source. Pellets of these powders are sintered at 800 0 C for 2hours in Nitrogen atmosphere. X-Ray Diffractograms of these samples showed that they possess polycrystalline nature and its phase varied from Hexagonal to Cubic. Lattice parameters of all the compounds are determined. The dc electrical Conductivity of these bulk pellets has been studied using the Keithley electrometer over the temperature range 77-300K. It is observed that electrical conductivity increases with the increase in Pb concentration. The electrical conductivity measurements show that Cd0.8-xPbxZn0.2S compounds possess mixed conduction at low temperatures and is observed that the conductivity of Cd0.8-xPbxZn0.2S, mixed Semiconductors is enhanced with the inclusion of Pb. The results are explained based on the defects included by Pb atoms.

Dislocation-assisted complex scattering mobility of electrons in plastically deformed n-GaAs single crystals

Abstract DC conductivity and Hall effect measurements are made in undeformed and plastically deformed (by indentation) n-type GaAs samples between 77 and 300 K. The studies show that the dislocation-assisted vacancy complexes of activation energy 0.015-0.010 eV are present in deformed samples. The electron mobility of these samples is explained by considering different scattering processes. In plastically deformed samples an additional scattering mobility due to dislocation-assisted vacancy complexes is suggested to explain the experimental mobilities. The centres responsible for this scattering are associated with native vacancy complexes segregated at the dislocation sites. The fresh dislocation motion, mainly α-dislocations (with higher mobility than β-dislocations) help the creation and movement of acceptor vacancies and their segregation as complexes at the dislocation sites. The complex scattering mobility of electrons has been found to vary linearly with temperature in all the deformed samples. These complexes are also found to be temperature-insensitive throughout the extrinsic region of the sample.