Investigations on Photoconductivity and Electrical Switiching in Selected Chalcogenide Glasses

Content Provider	CUSAT-Thesis
Advisor	Dr. Jacob, Philip
Researcher	Gregorios, Mathew
Abstract	In this thesis, we present the results of our investigations on the photoconductingand electrical switching properties of selected chalcogenide glass systems. We have usedXRD and X-ray photoelectron spectroscopy (XPS) analysis for confinuing the amorphousnature of these materials and for confirming their constituents respectively.Photoconductivity is the enhancement in electrical conductivity of materialsbrought about by the motion of charge carriers excited by absorbed radiation. Thephenomenon involves absorption, photogeneration, recombination and transport processesand it gives good insight into the density of states in the energy gap of solids due to thepresence of impurities and lattice defects. Photoconductivity measurements lead to thedetermination of such important parameters as quantum efficiency, photosensiti\'ity,spectral sensitivity and carrier lifetime. Extensive research work on photoconductingproperties of amorphous semiconductors has resulted in the development of a variety ofvery sensitive photodetectors. Photoconductors are finding newer and newer uses eyeryday. CdS, CdSe. Sb2S3, Se, ZnO etc, are typical photoconducting materials which are usedin devices like vidicons, light amplifiers, xerography equipment etc.Electrical switching is another interesting and important property possessed byseveral Te based chalcogenides. Switching is the rapid and reversible transition between ahighly resistive OFF state, driven by an external electric field and characterized by athreshold voltage, and a low resistivity ON state, Switching can be either threshold typeor memory type. The phenomenon of switching could find applications in areas likeinfonnation storage, electrical power control etc. Investigations on electrical switching inchalcogenide glasses help in understanding the mechanism of switching which isnecessary to select and modify materials for specific switching applications.Analysis of XRD pattern gives no further infonuation about amorphous materialsthan revealing their disordered structure whereas x-ray photoelectron spectroscopy,XPS)provides information about the different constituents present in the material. Also it gives binding energies (b.e.) of an element in different compounds and hence b.e. shift from theelemental form.Our investigations have been concentrated on the bulk glasses, Ge-In-Se, Ge-Bi-Seand As-Sb-Se for photoconductivity measurements and In-Te for electrical switching. Thephotoconducting properties of Ge-Sb-Se thin films prepared by sputtering technique havealso been studied. The bulk glasses for the present investigations are prepared by the meltquenching technique and are annealed for half an hour at temperatures just below theirrespective glass transition temperatures. The dependence of photoconducting propenies oncomposition and temperature are investigated in each system. The electrical switchingcharacteristics of In-Te system are also studied with different compositions and by varyingthe temperature.
File Format	PDF
Language	English
Publisher Institution	Cochin University of Science and Technology
Access Restriction	Open
Subject Keyword	Amorphous Semiconductors Photoconductivity Electrical switching X-ray photoelectron spectral analysis Chalcogenide Glasses Ge-In-Se glasses As-Sb-Se glasses In-Te glasses
Content Type	Text
Educational Degree	Doctor of Philosophy (Ph.D.)
Resource Type	Thesis