Fingerprints in the Optical and Transport Properties of Quantum Dots

The book "Fingerprints in the optical and transport properties of quantum dots" provides novel and efficient methods for the calculation and investigating of the optical and transport properties of quantum dot systems. This book is divided into two sections. In section 1 includes ten chapters where novel optical properties are discussed. In section 2 involve eight chapters that investigate and model the most important effects of transport and electronics properties of quantum dot systems This is a collaborative book sharing and providing fundamental research such as the one conducted in Physics, Chemistry, Material Science, with a base text that could serve as a reference in research by presenting up-to-date research work on the field of quantum dot systems

Spintronics: Fundamentals and applications

Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics.Comment: invited review, 36 figures, 900+ references; minor stylistic changes from the published versio

Light Matter Interaction in Epsilon Near Zero Metal/Insulator Layered Nanocavities Thesis

Light-matter interaction has been a widely investigated phenomena enlarging the area of nanophotonics beyond the limit. This stand out to be the back bone for future generation optical devices. Light confinement and propagation in a small volume gives rise to several rich optical properties. This can be realized in different type of nanostructured materials. Metal(M)/Insulator(I) multilayer nanocavities are highly versatile systems for light confinement and wave guiding at nanoscale. Their physical behavior is discussed successfully by electromagnetic theory. However, it is still obscured about the nature of cavity modes in layered metal/insulator nanocavities. The reason why such cavity mode can be excited without having any momentum matching technique are yet to be investigated. We start with a quantum treatment of the MIM as a double barrier quantum well where the resonant modes are assisted by tunneling of photons. The lossless characteristics of these modes with zero wavevector condition are inherent to the epsilon-nearzero (ENZ) band. We further investigated the coupling between epsilon near zero assisted volume plasmons in MIMIM nanocavities where one MIM cavity placed above the other. Strong coupling has been demonstrated in this system by an anticrossing of the ENZ modes in the individual cavities, where the splitting depends strongly on the thickness of the central metal layer. The properties of ENZ bulk plasmon modes for MIM and MIMIM systems are exploited to achieve both enhancement of spontaneous emission and decay rate of the perovskite nanocrystal film placed on the top of the nanocavity. However, the enhancement is within the limit of weak coupling regime. In order to achieve strong coupling between ENZ mode of cavity and emission mode of the fluorophore, one need to embed the fluorophore inside the cavity. But it has been realized that in such a case, long term stability of fluorophore by retaining its original optical properties are primary challenges. We studied the optical properties of nanocrystal layer that were overcoated with alumina by atomic layer deposition. This enabled us to effectively embed the NCs inside the dielectric layers of planar MIM and MIMIM nanocavities

Nuclear spin physics in quantum dots: an optical investigation

The mesoscopic spin system formed by the 10E4-10E6 nuclear spins in a semiconductor quantum dot offers a unique setting for the study of many-body spin physics in the condensed matter. The dynamics of this system and its coupling to electron spins is fundamentally different from its bulk counter-part as well as that of atoms due to increased fluctuations that result from reduced dimensions. In recent years, the interest in studying quantum dot nuclear spin systems and their coupling to confined electron spins has been fueled by its direct implication for possible applications of such systems in quantum information processing as well as by the fascinating nonlinear (quantum-)dynamics of the coupled electron-nuclear spin system. In this article, we review experimental work performed over the last decades in studying this mesoscopic,coupled electron-nuclear spin system and discuss how optical addressing of electron spins can be exploited to manipulate and read-out quantum dot nuclei. We discuss how such techniques have been applied in quantum dots to efficiently establish a non-zero mean nuclear spin polarization and, most recently, were used to reduce fluctuations of the average quantum dot nuclear spin orientation. Both results in turn have important implications for the preservation of electron spin coherence in quantum dots, which we discuss. We conclude by speculating how this recently gained understanding of the quantum dot nuclear spin system could in the future enable experimental observation of quantum-mechanical signatures or possible collective behavior of mesoscopic nuclear spin ensembles.Comment: 61 pages, 45 figures, updated reference list, corrected typographical error

Top-Down Etched Site-Controlled InGaN/GaN Quantum Dots.

Quantum technologies such as quantum communication and computation may one day revolutionize the landscape of communication and computing industry, which so far has been largely based on the classical manipulation of the flow of many photons and electrons. Many important quantum technologies have been demonstrated on single atoms which have discrete energy levels and can interact strongly with light, both functionalities are key to quantum technologies. However, single atoms are difficult to integrate with other photonic and electronic components, which are equally crucial to most of the applications. Semiconductor quantum dots are considered as the key building block to scalable quantum technologies due to their atom-like functionality and solid-state integrability. To date, many proof-of-principle integrated quantum devices have been demonstrated based on single quantum dots. However, most of the devices were not suitable for large-scale practical applications mainly due to the adoption of self-assembled III-As quantum dots, which form at random sites and operate only at liquid-helium temperatures. These drawbacks may be resolved by using III-N quantum dots with controlled forming site and optical properties, and high operating temperatures. This thesis studies site-controlled InGaN/GaN quantum dots fabricated by top-down etching a planar single quantum well. Compared to other existing site-controlled III-N quantum dots, ours have the following advantages: 1) the fabrication approach allows flexible control of the emission energy, oscillator strength and polarization of each quantum dot; 2) their emission is free from wetting layer contamination leading to purer single-photon emission; 3) they can be efficiently driven by electrical current. We demonstrate in this thesis that these quantum dots have all the essential properties required for most quantum technologies. They are efficient light emitters due to the strain relaxation that enhances the radiative recombination and limits the nonradiative surface recombination. They have discrete energy levels due to the strong exciton-exciton interaction by the small lateral size, manifested by both optically and electrically driven single-photon sources using our quantum dots. Finally, the net charges in each quantum dot can be controlled electrically via Coulomb blockade, which enables the understanding of exciton charging and fine structures crucial to many quantum technologies.PhDPhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111576/1/zlei_1.pd

Memory and Coupling in Nanocrystal Optoelectronic Devices

Optoelectronic devices incorporating semiconducting nanocrystals are promising for many potential applications. Nanocrystals whose size is below the exciton Bohr radius have optical absorption and emission that is tunable with size, due to the quantum confinement of the charge carriers. However, the same confinement that yields these optical properties also makes electrical conduction in a film of nanocrystals occur via tunneling, due to the high energy barrier between nanocrystals. Hence, the extraction of photo-generated charge carriers presents a significant challenge. Several approaches to optimizing the reliability and efficiency of optoelectronic devices using semiconducting nanocrystals are explored herein. Force microscopy is used to investigate charge behavior in nanocrystal films. Plasmonic structures are lithographically defined to enhance electric field and thus charge collection efficiency in two-electrode nanocrystal devices illuminated at plasmonically resonant wavelengths. Graphene substrates are shown to couple electronically with nanocrystal films, improving device conduction while maintaining carrier quantum confinement within the nanocrystal. And finally, the occupancy of charge carrier traps is shown to both directly impact the temperature-dependent photocurrent behavior, and be tunable using a combination of illumination and electric field treatments. Trap population manipulation is robustly demonstrated and verified using a variety of wavelength, intensity, and time-dependent measurements of photocurrent in nanogap nanocrystal devices, emphasizing the importance of measurement history and the possibility of advanced device behavior tuning based on desired operating conditions. Each of these experiments reveals a path toward understanding and optimizing semiconducting nanocrystal optoelectronic devices