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Epitaxy and physical properties of the structural mismatched thin films of chalcogenides and oxides


Author: Belenciuc Alexandr
Degree:doctor of physics and mathematics
Speciality: 01.04.07 - Condensed matter physics
Year:2010
Scientific adviser: Valeriu Canţer
doctor habilitat, professor, Institute of the Electronic Engineering and Nanotechnologies, Academy of Sciences of Moldova
Institution:
Scientific council:

Status

The thesis was presented on the 15 September, 2010
Approved by NCAA on the 4 November, 2010

Abstract

Adobe PDF document0.58 Mb / in romanian
Adobe PDF document0.87 Mb / in russian

Keywords

Epitaxy, thin films, superlattices, lattice mismatch, incommensurate interface, strain relaxation, fluorides, A4B6 semiconductors, manganites, photodetectors, magnetotransport

Summary

The thesis is devoted to study heteroepitaxial systems with a large lattice parameter mismatch. Two different heavy mismatched heterosystems were investigated: (1) chalcogenides A4B6 (PbTe and Pb1-xSnxTe) on Si(111) substrates with a buffer layer of BaF2, and (2) complex oxides, manganites La0.7(Ca, Sr)0.3MnO3, on substrates of MgO(100).

Comparative analysis of BaF2 epitaxial growth on Si(111) and on CaF2(111)/Si(111) was carried out. It was established that epitaxy of BaF2 directly on Si(111) without intermediate layer CaF2 occurred by a layered growth mechanism leading to residual stress reduction and to surface morphology improving. There is full residual stress relaxation on thick films PbTe and Pb1 xSnxTe grown at such buffer layers. La0.7(Ca,Sr)0.3MnO3 epitaxy at optimal supersaturation on MgO(100) also showed absence of residual stresses. It was offered an explanation of obtained results based on an incommensurate interface formation and epitaxy with matching domains rather than lattices. For oxide heterosystem a direct confirmation of the incommensurate interface formation was obtained. It has been demonstrated that layered growth mechanism and the absence of residual pressure lead to substantial improvement of the material properties.

The results of the heterosystems studies were used to obtain and investigate a number of new film structures. Arrays of far-IR photodetectors on Si were first created on the basis of Pb1 xSnxTe:In films grown on Si with fluorură ide buffer and their photosensitivity was studied. PbTe/CdTe superlattices were obtained for the first time and interdiffusion coefficient between the materials was determined. PbTe/SnTe superlattices were first grown on Si with fluorură ide buffer and residual stresses on the superlattice layers were determined. A-cation ordering was firstly discovered on La0.75Ca0.25MnO3 layers and structural model of the ordered material was constructed. Large magnetocapacitance effect was found on La0.7Ca0.3MnO3/BaTiO3 superlattices. The effect origin based on formation of the incommensurate interface between superlattice and substrate was suggested. Vertical two-phase epitaxial nanocomposite films (La0.7Ca0.3MnO3)1-x:(MgO)x were first obtained and studied. It was demonstrated that an elastic interaction between two phases determined the composite films properties.

The obtained results were published in 19 scientific papers and 4 patents.

The thesis consists of introduction, 4 chapters and overall conclusions.

The thesis is written in Russian and contains 136 pages of basic text, 55 figures, 5 tables and 150 references.