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CNAA / Theses / 2018 / July /


Author: Marina Ciobanu
Degree:doctor of physics and mathematics
Speciality: 01.04.10 - Semiconductors physics and engineering
Scientific advisers: Dumitru Ţiuleanu
doctor habilitat, professor, Technical University of Moldova

Institution: Technical University of Moldova


The thesis was presented on the 5 July, 2018
Approved by NCAA on the 23 November, 2018


Adobe PDF document1.46 Mb / in romanian


CZU 621.315.592

Adobe PDF document 6.98 Mb / in romanian
161 pages


amorphous material, As2 S3 Ge8 -Te, contact, impedance, capacitance, transport mechanism, work function, gas sensors


The field of investigations: Physics and engineering of glassy chalcogenide semiconductors, contact properties and surface phenomena in quaternary chalcogenides by interaction with gases.

Thesis aim: The study of the influence of contacts and surface phenomena on the electric charge transport mechanism in quaternary glassy chalcogenides based on sulfur and tellurium, for their application in chemical transducers.

Objectives: Preparation and structural analysis of thin solid films based of new quaternary chalcogenides in the As2 S3 Ge8 -Te system, fabrication of functional structures based on these materials with electrodes of different metals such as (Ag, Pt, In), the study of their direct current conductive properties and capacitance for the purpose of selecting ohmic contacts, identification of the electric charge transport mechanisms and of the basic semiconductor parameters of the materials in question. Study of the electric charge transport under the conditions of the alternating current, the elucidation of the transport mechanisms via jumps between localized states in the forbidden gap, the estimation of the density and the energy distribution of these states. The study of the influence of surface phenomena by gas adsorption on the impedance, capacitance, work function and transport mechanisms, the realization and characterization of the gas sensors based on chalcogenides in question, operable at the room temperature by variation of the impedance, capacitance or work function.

Novelty and scientific originality: New quaternary chalcogenides As2Te13Ge8S3 and As2 Te130 Ge8 S3 have been synthesized and thin films based on them were grown and studied. The semiconductor parameters of these materials were determined: the width of forbidden gap, the position of the stationary Fermi level and the concentration of states located in its vicinity, the energy domain of the localized states of the valence band's tail and the energy requested for jumping of charge carriers between these states. The mechanisms of charge transport have been established in these materials. It was definitely demonstrated the recuperative variation of capacitance, surface conductivity and work function of quaternary chalcogenide thin films by gas interaction, as well as the physical models of their interaction with nitrogen dioxide and / or water vapor were developed. For the first time, the hypothesis has been suggested, which we have later confirmed experimentally, that the interaction of gases with the surface of the chalcogenide glassy semiconductors, together with the variation of the charged state of the surface, may also lead to modification of the dominant mechanism of conductivity, phenomenon available only in disordered semiconductors.

Applicative value of the work: Have been formulated the operating concepts and were elaborated the experimental gas transducers based on glassy As2 S3 Ge8 -Te, operable at room temperature by variation of impedance, capacitance or work function.

The resultshave been published in 16 scientific papers, three of which in international journals with impact factor. The work was supported by nominal scholarship for excellence, provided by the Government of the Republic of Moldova.