Electronic Structure And Optical Properties Of Sb Based Self Assembled Quantum Dots For The Mid Infrared Range
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| Author | : Gik Hong Yeap |
| Publisher | : |
| Total Pages | : |
| Release | : 2009 |
| Genre | : |
| ISBN | : |
Quantum dots (QDs) are zero-dimensional nanostructures that confined carriers in three dimensions comparable to their de Broglie wavelengths. Therefore, carriers exhibit?-shaped energy levels and densities of states. Due to their band structure, QD systems show significant advantages as active regions in laser cavities, both in term of lower threshold current densities and better thermal behaviour. The most studied system being InAs/GaAs system but the antimonide-based (Sb-based) material system has been paid much attention due to their potential for optical devices in the 3-5?m (0.25-0.40 eV) spectral regions and motivated by feasibility of active medium in high speed electronic and long wavelength photonic devices. In most cases, QDs structures had been obtained with an intrinsic elastic strain field arising from the lattice mismatch between the matrix and QD materials. The strain field plays a very significant role in the fabrication of the self-assembled QDs (SAQDs). Strain fields inside SAQD structures strongly affect the electronic band structure, which in turn, strongly affects the performance of optoelectronic devices. Therefore, knowledge and determination of the strain field in the dots and surrounding matrix is crucial in order to obtain a well ordered SAQDs structure. While knowledge and determination of the electronic structure calculation are necessary for further device modelling to improve the performance of the devices. Numerical work based on continuum-elasticity based on Finite Element Method (FEM) and standard-deformation-potential theory has been carried out to investigate the effect of strain on the band structure for InSb-based SAQD systems with type-I and type-II band alignment. The effect of elastic anisotropy on both strain distribution and band edges profile is also performed. Next, multi-band k?p method is used to model the electronic structure of InSb-based SAQD systems. The results from the modelling show that the strain-modified band profile of the zinc-blende III-V compound semiconductor SAQDs is not very sensitive to the details of the dot shape and the major governing parameter of the geometry is the aspect ratio of the dot. The modelling results also reveal that there are no appropriate material combinations for zinc-blende III-V compound semiconductors that would applicable for the MIR 3-5?m (0.25-0.40 eV) emission range when type-I band alignment is possible. This leads to the investigation of type-II broken gap InAsxSb(1-x)/InAs SAQDs. Finally, the optical properties of the InSb-based SAQDs are investigated by means of the photoluminescence (PL) measurement using Fourier transform infrared (FT-IR) spectroscopy. The PL results are analysed and compared to the modelling results.
| Author | : Zhiming M Wang |
| Publisher | : Springer Science & Business Media |
| Total Pages | : 470 |
| Release | : 2007-11-29 |
| Genre | : Technology & Engineering |
| ISBN | : 0387741917 |
This multidisciplinary book provides up-to-date coverage of carrier and spin dynamics and energy transfer and structural interaction among nanostructures. Coverage also includes current device applications such as quantum dot lasers and detectors, as well as future applications to quantum information processing. The book will serve as a reference for anyone working with or planning to work with quantum dots.
| Author | : Weidong Yang |
| Publisher | : |
| Total Pages | : 312 |
| Release | : 1999 |
| Genre | : Molecular electronics |
| ISBN | : |
| Author | : Hock Jin Quah |
| Publisher | : Trans Tech Publications Ltd |
| Total Pages | : 245 |
| Release | : 2023-07-27 |
| Genre | : Science |
| ISBN | : 3036410066 |
Selected peer-reviewed extended articles based on abstracts presented at the 2nd International Conference on Semiconductor Materials and Technology (ICoSeMT 2021) Aggregated Book
| Author | : Saumya Sengupta |
| Publisher | : Springer |
| Total Pages | : 77 |
| Release | : 2017-08-04 |
| Genre | : Technology & Engineering |
| ISBN | : 9811057028 |
This book explores the effects of growth pause or ripening time on the properties of quantum dots(QDs). It covers the effects of post-growth rapid thermal annealing (RTA) treatment on properties of single layer QDs. The effects of post-growth rapid thermal annealing (RTA) treatment on properties of single layer QDs are discussed. The book offers insight into InAs/GaAs bilayer QD heterostructures with very thin spacer layers and discusses minimum spacer thickness required to grow electronically coupled bilayer QD heterostructures. These techniques make bilayer QD heterostructures a better choice over the single layer and uncoupled multilayer QD heterostructure. Finally, the book discusses sub-monolayer (SML) growth technique to grow QDs. This recent technique has been proven to improve the device performance significantly. The contents of this monograph will prove useful to researchers and professionals alike.
| Author | : Lucjan Jacak |
| Publisher | : Springer Science & Business Media |
| Total Pages | : 176 |
| Release | : 2013-06-29 |
| Genre | : Technology & Engineering |
| ISBN | : 3642720021 |
We present an overview of the theoretical background and experimental re sults in the rapidly developing field of semiconductor quantum dots - systems 8 6 of dimensions as small as 10- -10- m (quasi-zero-dimensional) that contain a small and controllable number (1-1000) of electrons. The electronic structure of quantum dots, including the energy quan tization of the single-particle states (due to spatial confinement) and the evolution of these (Fock-Darwin) states in an increasing external magnetic field, is described. The properties of many-electron systems confined in a dot are also studied. This includes the separation of the center-of-mass mo tion for the parabolic confining potential (and hence the insensitivity of the transitions under far infrared radiation to the Coulomb interactions and the number of particles - the generalized Kohn theorem) and the effects due to Coulomb interactions (formation of the incompressible magic states at high magnetic fields and their relation to composite jermions), and finally the spin-orbit interactions. In addition, the excitonic properties of quantum dots are discussed, including the energy levels and the spectral function of a single exciton, the relaxation of confined carriers, the metastable states and their effect on the photoluminescence spectrum, the interaction of an exciton with carriers, and exciton condensation. The theoretical part of this work, which is based largely on original re sults obtained by the authors, has been supplemented with descriptions of various methods of creating quantum-dot structures.
| Author | : Juraj Marek |
| Publisher | : Trans Tech Publications Ltd |
| Total Pages | : 131 |
| Release | : 2023-05-31 |
| Genre | : Science |
| ISBN | : 3036413316 |
Special topic volume with invited peer-reviewed papers only
| Author | : Tuan Anh Nguyen |
| Publisher | : |
| Total Pages | : 218 |
| Release | : 2006 |
| Genre | : |
| ISBN | : |
In this dissertation, we use different optical and imaging spectroscopy techniques to study electronic structure and optical properties of CdTe/ZnTe and CdSe/ZnSe self-assembled quantum dots (SAQDs). We perform single dot photoluminescence excitation experiments to identify carrier excitation mechanisms in CdTe/ZnTe QDs. The first mechanism is direct excitation into the QD excited states followed by relaxation to the ground state and the second mechanism is direct excitation into the QD ground states through LO phonon-assisted absorption. We then execute resonant PL measurements for both CdTe and CdSe QD ensembles to study the dependence of exciton-LO phonon coupling on QD size in these II-VI SAQDs. We shown that the strength of exciton-LO phonon coupling increases significantly for QDs with lateral sizes smaller than the exciton Bohr radius (e.g. as-grown CdTe QDs) while for larger QDs (e.g. CdSe or CdTe annealed) it is almost independent of the QD emission energy, and therefore presumably of the QD size. In order to study electronic coupling between SAQDs, we setup imaging experiments with the use of a hemisphere solid immersion lens. While the PLE imaging measurements show the existence two-dimensional platelets with a typical size of about 500 nm which provide spatially extended but strong localized states through which different QDs could be populated simultaneously, the spatially resolved imaging data demonstrates a complete 2D map of those platelets. These results are further supported by computational calculations based on finite element analysis. Low temperature exciton spin relaxation in symmetric CdTe SAQDs has been thoroughly studied by means of cw polarized magneto-PL and polarized time-resolved PL spectroscopies. We find that the degeneracy of exciton energy levels has a strong influence on the spin transition. When the exciton spin states in QDs are degenerate, the spin relaxation time is much shorter than the exciton recombination time. In contrast, if this degeneracy is removed, either by asymmetry or an external magnetic field, the spin relaxation time becomes much longer than the exciton recombination time. Using simple rate equation models, we estimate exciton spin relaxation times equal to 4.8 ns and 50 ps for non-degenerate and degenerate QD states, respectively.
| Author | : |
| Publisher | : Academic Press |
| Total Pages | : 385 |
| Release | : 1999-03-29 |
| Genre | : Technology & Engineering |
| ISBN | : 0080864589 |
This volume is concerned with the crystal growth, optical properties, and optical device application of the self-formed quantum dot, which is one of the major current subjects in the semiconductor research field.The atom-like density of states in quantum dots is expected to drastically improve semiconductor laser performance, and to develop new optical devices. However, since the first theoretical prediction for its great possibilities was presented in 1982, due to the difficulty of their fabrication process. Recently, the advent of self-organized quantum dots has made it possible to apply the results in important optical devices, and further progress is expected in the near future.The authors, working for Fujitsu Laboratories, are leading this quantum-dot research field. In this volume, they describe the state of the art in the entire field, with particular emphasis on practical applications.
| Author | : Malte Huck |
| Publisher | : diplom.de |
| Total Pages | : 137 |
| Release | : 2010-03-25 |
| Genre | : Science |
| ISBN | : 3836644398 |
Inhaltsangabe:Abstract: Chapter 1: In this thesis we investigate the optical properties of self-assembled quantum dots exposed to a lateral electric field. As a result of the electric field the wave functions of electrons and holes inside the quantum dot are manipulated, which makes it possible to tune their energy levels and control the optical properties of the system. The possibility of tuning the emission energy of different few particle states using this method makes this system very promising for the use of a source of polarization entangled photons as discussed in the following sections. In Section 1.1 the concept of entangled states is introduced together with a brief historical overview. The possibility of using the exciton biexciton cascade of a self-assembled quantum dot for the generation of entangled photon pairs is presented in Section 1.2. Chapter 2: In this chapter we introduce the concept of quantum dots and demonstrate their optical emission properties. In Section 2.1 the quantum dot is introduced as a three-dimensional charge carrier trap. Several types of quantum dots are presented in an overview. In Section 2.2 we discuss the physical effects that occur on the way from bulk semiconductor material to the three-dimensional charge carrier confinement in the case of quantum dots. The growth of self-assembled quantum dot samples is the topic of Section 2.3, where the technique of molecular beam epitaxy is introduced (Section 2.3.1). This technique is used to grow the semiconductor quantum dots via heteroepitaxy in the Stranski-Krastanov growth mode (Section 2.3.2). Quantum dots are commonly referred to as artificial atoms due to their atomlike emission features. The origin for this expression is explained in Section 2.4 on the basis of the energetic structure of self-assembled quantum dots. The optical properties of quantum dots are discussed in Section 2.5, beginning with an introduction to the experimental setup that has been used to investigate the quantum dots during this thesis (Section 2.5.1). Different optical excitation modes are presented in Section 2.5.2 and in Section 2.5.3 we discuss, how to achieve a low enough quantum dot density on the analyzed samples. Section 2.5.4 deals with the photoluminescence of different exciton states and in Section 2.5.5 we present how these lines can be identified via power dependent measurements. Finally, the concept of initial charges in self-assembled quantum dots is presented in [...]
