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Low dimensional electron states and effects in the quantum tructures on the base of semiconductors IV-VI and bismuth


Author: Igor Bejenari
Degree:doctor of physics and mathematics
Speciality: 01.04.07 - Condensed matter physics
Year:2006
Scientific adviser: Valeriu Canţer
doctor habilitat, professor, Institute of the Electronic Engineering and Nanotechnologies
Institution:

Status

The thesis was presented on the 18 September, 2006
Approved by NCAA on the 26 October, 2006

Abstract

Adobe PDF document0.28 Mb / in romanian
Adobe PDF document0.30 Mb / in russian

Thesis

CZU 538.91:[539.21:537.311.322]

Adobe PDF document 1.41 Mb / in russian
174 pages


Keywords

heterojunction, nanowire, electron state, dimensional quantization effect, magnetophotogalvanic effect, Aharonov-Bohm effect, semimetal-semiconductor transition, anisotropy, PbTe/Pb1-xSnxTe, Bi, Bi2Te3, two band kp approximation, Seebeck coefficient

Summary

The dissertation is intended to study electron states and effects in the heterojunctionPbTe/Pb1-xSnxTe, nanowires of bimuth and bismuth telluride. The comparative analysis of the interface states was performed in the framework of the linear and step-like heterojunction. The direct analogy between the interface state energy values and corresponding wave functions is obtained independent of boundary conditions at the interface. The energy spectrum and wave functions of the electron states were studied in the framework of the two band model of the linear and step heterojunction PbTe/Pb0.88Sn0.12Te in the parallel magnetic field taking into account the induced polarization in the layers. It is stated that the parallel magnetic field leads to breaking of energy spectrum inversion of charge carriers E(-k)≠E(k) in the strained heterojunction. The nondissipative magnetophotogalvanic current is calculated in the heterojunction interface plane. The anisotropic effective mass method is elaborated for analytical calculation of the energy spectrum and wave functions of charge carriers in the cylindrical Bi nanowires with the infinite large potential barrier on the surface. The motion of the carriers with anisotropic effective mass is obtained to be restricted by the elliptic or hyperbolic caustic. The mass anisotropy leads to orbital splitting of the energy subbands and amplification of the confinement effect. Hence, the semimetal-semiconductor transition takes place at the considerably larger diameters than it was predicted in the framework of the quasi-isotropic model so far. The energy spectrum and wave function of carriers were studied by using pattern problem method and finite difference method in bismuth nanowires in the weak longitudinal magnetic field. The electron states are found to be divided into the surface, ring, hyperbolic caustic, and harmonic oscillator states in dependence of the type of carrier motion in the Bi nanowire cross section. It was deduced, that the noninteger period from the interval (1÷4.2)Фо of the magnetic flux quantization in Bi nanowire is expressed by formula ∆Ф=ФоS/Sec, where S is transverse section area, Sec is area of the surface bounded by the elliptic caustic, Фо=h/e is magnetic flux quantum. The radial electric field effect on the thermoelectric properties of bismuth telluride nanowires of different conductivity type is investigated. It is obtained that the figure of merit ZT of undoped nanowires increases about twice under the electric field influence.

The obtained results were published in 19 scientific papers. The thesis is written in Russian language and it consists of 95 text pages, 47 figures, 4 tables, and 217 references.