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Physical properties of one-and bi-dimensional semiconductor structures and composites


Author: Postolache Vitalie
Degree:doctor of physics and mathematics
Speciality: 01.04.10 - Semiconductors physics and engineering
Year:2019
Scientific adviser: Ion Tighineanu
doctor habilitat, professor, Institute of Mathematics and Computer Science of the ASM
Scientific consultant: Veaceslav Ursachi
doctor habilitat, associate professor (docent), Institute of Applied Physics of the ASM
Institution: Technical University of Moldova

Status

The thesis was presented on the 12 June, 2019 at the meeting of the Scientific Council and now it is under consideration of the National Council.

Abstract

Adobe PDF document1.96 Mb / in romanian

Thesis

CZU 621.315.592

Adobe PDF document 6.25 Mb / in romanian
157 pages


Keywords

III-V semiconductors, zinc oxide, hybrid nanomaterials, aerographite, magnetic alloys, filiform nanostructures, persistent photoconductivity, luminescence, plasmonic effects, magnetic properties, magnetic bistability

Summary

The structure of the thesis: introduction, 4 chapters, general conclusions and recommendations, bibliography of 215 titles, 5 annexes, 122 pages of basic text, 75 figures and 6 tables. The results presented in the thesis were published in 15 scientific papers.

Field of study: nanotechnology and novel functional nanomaterials.

The aim of the work is to explore photoelectric and plasmonic effects in quasi-onedimensional and two-dimensional nanostructures as well as in nanoporous and composite materials prepared on the basis of III-V materials and ZnO, and to explore magnetic, galvanomagnetic and photonic properties of filiform structures from Ge and alloys in glass isolation.

Objectives: preparation of semiconductor and magnetic filiform, porous, membrane-type and composite materials; comparative study of their photoelectrical properties with a special focus on photoconductivity relaxation for identifying the mechanisms of persistent photoconductivity; elucidation of the impact of thin metal film deposition on nanostructured semiconductor layers upon photoluminescence intensification by means of plasmonic effects; development of techniques for measuring magnetic properties of filiform structures; investigation of filiform nanostructures produced by stretching and estimation of prospects for their application.

Novelty and scientific originality. Technological parameters have been identified which ensure controlled modification of the morphology of semiconductor nanostructured layers, ultrathin membranes, nanowires and hybrid three-dimensional nanomaterials. Broadband photoabsorption has been demonstrated for the first time in hybrid aerographite-ZnO structures; reasons and mechanisms of this phenomenon have been elucidated. Peculiarities of long duration photoconductivity relaxation and the mechanisms of persistent photoconductivity in semiconductor nanostructures have been determined as compared to bulk materials. The mechanisms of photoluminescence intensification have been identified in nanostructured semiconductor layers covered by thin conductive films. Technology for integration of a record number of Ge nanowires (up to 1 mln) in a glass fiber has been developed, and conditions for ensuring the continuity of the filiform nanostructure core have been determined. The effect of galvano-magnetic recombination in Ge nanowires, the effect of magnetic microwire interaction and the Wiegand-type effect in a microwire bunch have been realiazed.

The solved scientific problem is the identification of persistent photoconductivity mechanisms as a function of composition and morphology of semiconductor nanostructures, exploration of plasmonic effects for intensification of luminescence, and photonic, magnetic and galvano-magnetic properties in filiform nanostructures. Theoretical significance and practical value of the work. The mechanisms of persistent photoconductivity, optical quenching, and plasmonic effects have been determined as a function composition and morphology of semiconductor nanostructures. These results can be employed for diminution of the negative impact upon devices, improving their parameters, exploration of memory effects and increasing the emission efficiency. The observed effects in filiform nanostructures can be employed in magnetic sensors and labels, photonic devices and other applications.