Author: Ramūnas Nedzinskas
Dissertation title: Modulated reflectance and photoluminescence spectroscopy of epitaxial InGaAs quantum dot structures
Fields of science: Physical sciences, Physics (02P), Semiconductor physics (P 265)
Scientific supervisor: Prof. Habil. Dr. Gintaras Valušis
Defence of the dissertation: 2012-09-24
Epitaxial InGaAs quantum dot (QD) structures is the topic of this doctoral dissertation. The QD structures are studied using modulated reflectance and photoluminescence spectroscopy techniques. Such nanostructures are the key-ingredients in many novel photonics devices, operating in infrared and terahertz spectral range. Hence, a comprehensive knowledge of optical properties and electronic energy spectrum of these QD structures is essential in order to define their optimal design parameters and favorable growth conditions.
The doctoral thesis is organized as follows. Motivation, main aims of the work, scientific novelty, statements for defence and list of publications together with a list of conference reports are given in the Introduction. Then, Chapter 1 presents the principles and examples of modulation spectroscopy, a very sensitive tool for optical characterization, followed by a brief introduction to molecular beam epitaxy and Stranski-Krastanow self-assembling growth mode for realization of QD nanostructures. Moreover, an extensive literature overview, regarding main achievements of QD-based nanostructures investigated, can be found here. In Chapter 2, details of QD samples studied with the relevant structure schemes, bandstructure diagrams, growth protocols and TEM images followed by experimental set-up of spectroscopic techniques employed are given. Chapters 3 and 4 covers original results of the dissertation. In particular, Chapter 3 contains comprehensive investigation of electronic structure and optical properties of InAs/GaAs/AlAs dots-in-a-superlattice, InAs/InGaAs/GaAs/AlAs dots-in-a-well and InGaAs quantum rod (QR) structures. Moreover, an intriguing optical anisotropy properties of InGaAs QRs are revealed and discussed therein. Chapter 4 is devoted to original analytical approach, based upon variable separation approximation, for energy spectrum calculations of cylindrical self-assembling QDs and QRs. Finally, Chapter 5 underlines the main results and presents conclusions of the work.