Using Time-resolved Photoluminescence Spectroscopy to Examine Exciton Dynamics in II-VI Semiconductor Nanostructures PDF Download
Are you looking for read ebook online? Search for your book and save it on your Kindle device, PC, phones or tablets. Download Using Time-resolved Photoluminescence Spectroscopy to Examine Exciton Dynamics in II-VI Semiconductor Nanostructures PDF full book. Access full book title Using Time-resolved Photoluminescence Spectroscopy to Examine Exciton Dynamics in II-VI Semiconductor Nanostructures by Laura M. Robinson. Download full books in PDF and EPUB format.
Author: Laura M. Robinson Publisher: ISBN: Category : Languages : en Pages :
Book Description
We use photoluminescence spectroscopy to investigate the optical properties of two different II-VI semiconductor nanostructure systems: ZnMnSe/ZnSe multiple quantum wells and self-assembled CdSe quantum dots. The behavior of excitons in ZnMnSe quantum wells is examined using polarized magneto-photoluminescence, while (temperature-dependent) time-resolved photoluminescence is used to study the dynamics of excitons confined to quantum dot structures. When Zn0.86Mn0.14Se/ZnSe multiple quantum wells are placed in an external magnetic fields, the spin-down holes become confined to the ZnMnSe "barriers," while the electrons remain in the ZnSe "wells." This spatial separation of electrons and holes results in weak electron-hole overlap, which should result in a large increase of the radiative lifetime of the spin-down exciton. As a result, we see the formation of exciton magnetic polarons (EMP) which lower their energy by spontaneously aligning the magnetic impurities in the exciton Bohr radius. We find that the EMP polarization approaches 100% in fields as small as 200 mT in these spatially indirect EMP, which is consistent with their extremely long recombination lifetime (%7E10 ns). This contrasts with previous measurements on other magnetic quantum well systems for which the polarization of short-lived spatially direct EMP never saturates. Time-resolved photoluminescence measurements of excitons confined to CdSe self-assembled quantum dots (SAQDs) reveal the existence of two different exciton decay times: a short 450 ps lifetime and a much longer (> 4 ns) lifetime. While the emission resulting from the short lifetime excitons persists to room temperatures, the longlifetime component decreases in intensity with increasing temperature and is nearly completely gone by 60 K. Time-resolved spectra further reveal that the long lifetime component arises from spectrally sharp features (%7E200eV), while the rapid decay results from an underlying broad emission (%7E60 meV). Further analysis reveals that both states exhibit an activated behavior with activation energies that differ by over an order of magnitude for the two components. These interesting differences may reflect the complex nature of the electron and hole wave functions confined to these CdSe structures.
Author: Laura M. Robinson Publisher: ISBN: Category : Languages : en Pages :
Book Description
We use photoluminescence spectroscopy to investigate the optical properties of two different II-VI semiconductor nanostructure systems: ZnMnSe/ZnSe multiple quantum wells and self-assembled CdSe quantum dots. The behavior of excitons in ZnMnSe quantum wells is examined using polarized magneto-photoluminescence, while (temperature-dependent) time-resolved photoluminescence is used to study the dynamics of excitons confined to quantum dot structures. When Zn0.86Mn0.14Se/ZnSe multiple quantum wells are placed in an external magnetic fields, the spin-down holes become confined to the ZnMnSe "barriers," while the electrons remain in the ZnSe "wells." This spatial separation of electrons and holes results in weak electron-hole overlap, which should result in a large increase of the radiative lifetime of the spin-down exciton. As a result, we see the formation of exciton magnetic polarons (EMP) which lower their energy by spontaneously aligning the magnetic impurities in the exciton Bohr radius. We find that the EMP polarization approaches 100% in fields as small as 200 mT in these spatially indirect EMP, which is consistent with their extremely long recombination lifetime (%7E10 ns). This contrasts with previous measurements on other magnetic quantum well systems for which the polarization of short-lived spatially direct EMP never saturates. Time-resolved photoluminescence measurements of excitons confined to CdSe self-assembled quantum dots (SAQDs) reveal the existence of two different exciton decay times: a short 450 ps lifetime and a much longer (> 4 ns) lifetime. While the emission resulting from the short lifetime excitons persists to room temperatures, the longlifetime component decreases in intensity with increasing temperature and is nearly completely gone by 60 K. Time-resolved spectra further reveal that the long lifetime component arises from spectrally sharp features (%7E200eV), while the rapid decay results from an underlying broad emission (%7E60 meV). Further analysis reveals that both states exhibit an activated behavior with activation energies that differ by over an order of magnitude for the two components. These interesting differences may reflect the complex nature of the electron and hole wave functions confined to these CdSe structures.
Author: Pradeep Bajracharya Publisher: ISBN: Category : Languages : en Pages : 163
Book Description
We study the dynamics of excitons in bimodal CdSe quantum dots. The effect of exciton localization is investigated by identifying transfer mechanisms due to thermalization and redistribution of excitons. We observe an exciton emission from low energy (QDs1) and weaker emission from high energy (QDs2) at low excitation levels at 10 K. Temperature-dependent photoluminescence (PL) studies reveal a thermally activated exciton transfer from QDs1 to QDs2. Time-resolved PL estimate the characteristic radiative and nonradiative decay rates as well as the trapping rate from the QD-precursor layer. The observed PL is reasonably reproduced using a coupled rate equation model. We investigate 10 nm Zn0.94Mg0.06Se/ZnSe quantum well (QW) with two-beam four-wave mixing (FWM) using 90 fs pulses. At high intensity the signal is dominated by & chi(3) FWM processes and at low intensity it reveals an exciton resonant phase coherent photorefractive (PCP) effect that is attributed to the formation of an electron grating within the QW by the interference of coherent QW excitons. The observed traces and spectra are reproduced by the model based on a 15-level system and a phenomenological PCP model. The dynamical properties of the electron grating responsible for the PCP is further studied reducing the pulse repetition at 45, 55 and 65 K. The PCP diffraction reveals a nearly constant efficiency up to 1 & mus that implies a constant average equilibrium electron density. With increasing temperature, the efficiency decreases due to QW electron escape back to the substrate reducing the grating lifetime. The observed PCP efficiency is studied with a model that considers the equilibrium density dynamics in the QW. We further report on PCP effect in Zn0.9Mg0.1Se/ZnSe QW by performing intensity dependent and polarization dependent two-beam FWM experiments using 30 fs pulses at 2.79 and 2.84 eV. The PCP effect is attributed to the formation of an electron grating within the QW by the interference of excitons in the ZnMgSe barrier. Model calculations based on the extended optical Bloch equations for a 17-level system and a modified PCP model reproduce most of the features of intensity and polarization dependent FWM spectra and traces. Three beam experiments support the observed PCP effect.
Author: Publisher: ISBN: Category : Languages : en Pages : 374
Book Description
The first part of this dissertation discusses GaSe monomer and aggregated particles. GaSe nano-disks have been prepared by several different synthetic methods. A study on the effect of various ligations suggests that well-aggregated stable particles are ligated by tight-binding alkyl phosphonic acid anhydrides. Addition of dodecyl aldehyde to particles that are primarily ligated by trioctylphosphine and trioctylphosphine oxide results in strongly coupled aggregates that cause a large red shift of the absorption spectrum (1600 cm-1) and the reversal of singlet and triplet states. This spin reversal results in changes in time-resolved anisotropy and a dramatic decrease in radiative lifetime. The quantum yield of particles increases from 4.7% in monomers to 61% in strongly coupled aggregates. GaSe aggregates can be mixed with a smectic-A phase liquid crystal, LC (4-octyl, 4'-cyanobiphenyl), where the liquid crystal forces the particles to form long stacks that are in line with the director axis of the LC. This only happens when the synthesized GaSe particles are extremely well-aggregated. The second part of this dissertation discusses the synthesis and exciton dynamics of various morphologies of CdTe/CdSe nano-heterostructures. Highly luminescent CdTe spherical nanoparticles with an average size of 3.4 nm are synthesized using a novel synthetic method that uses Octadecylphosphonic acid in the Te precursor. These particles can have a quantum yield of up to 90%. Core/shell and dot/tetrapod CdTe/CdSe heterostructures synthesized from these Te cores are used to study the biexciton Auger dynamics and the electron cooling rates in these structures by means of femtosecond transient absorption measurements. An effective mass approximation (EMA) is used to model the exciton dynamics, specifically Auger times, in these particles. Calculations of the electron and hole wavefunctions using the EMA model predict electron and hole overlap and radiative lifetimes that match those of t
Author: Writam Banerjee Publisher: CRC Press ISBN: 1040119107 Category : Technology & Engineering Languages : en Pages : 683
Book Description
In recent years, the abundant advantages of quantum physics, quantum dots, quantum wires, quantum wells, and nanocrystals in various applications have attracted considerable scientific attention in the field of nonvolatile memory (NVM). Nanocrystals are the driving elements that have helped nonvolatile flash memory technology reach its distinguished height, but new approaches are still needed to strengthen nanocrystal-based nonvolatile technology for future applications. This book presents comprehensive knowledge on nanocrystal fabrication methods and applications of nanocrystals in baseline NVM and emerging NVM technologies and the chapters are written by experts in the field from all over the globe. The book presents a detailed analysis on nanocrystal-based emerging devices by a high-level researcher in the field. It has a unique chapter especially dedicated to graphene-based flash memory devices, considering the importance of carbon allotropes in future applications. This updated edition covers emerging ferroelectric memory device, which is a technology for the future, and the chapter is contributed by the well-known Ferroelectric Memory Company, Germany. It includes information related to the applications of emerging memories in sensors and the chapter is contributed by Ajou University, South Korea. The book introduces a new chapter for emerging NVM technology in artificial intelligence and the chapter is contributed by University College London, UK. It guides the readers throughout with appropriate illustrations, excellent figures, and references in each chapter. It is a valuable tool for researchers and developers from the fields of electronics, semiconductors, nanotechnology, materials science, and solid-state memories.
Author: Marcin L. Sadowski Publisher: Springer Science & Business Media ISBN: 9401141584 Category : Science Languages : en Pages : 443
Book Description
Optical methods for investigating semiconductors and the theoretical description of optical processes have always been an important part of semiconductor physics. Only the emphasis placed on different materials changes with time. Here, a large number of papers are devoted to quantum dots, presenting the theory, spectroscopic investigation and methods of producing such structures. Another major part of the book reflects the growing interest in diluted semiconductors and II-IV nanosystems in general. There are also discussions of the fascinating field of photonic crystals. `Classical' low dimensional systems, such as GsAs/GaAlAs quantum wells and heterostructures, still make up a significant part of the results presented, and they also serve as model systems for new phenomena. New materials are being sought, and new experimental techniques are coming on stream, in particular the combination of different spectroscopic modalities.
Author: Chi-Hung Chuang Publisher: ISBN: Category : Languages : en Pages : 233
Book Description
My interest in the photoscience has been focused on the photoinduced charge carrier dynamics in heterostructured nanomaterials. Of particular interest are type-II heterostructures, where the relative band alignment of their constituent semiconductor materials promotes a spatial separation of the electron and hole following photoexcitation, a highly desirable property for photovoltaic applications. Femtosecond laser spectroscopy has been used to investigate charge transfer dynamics with a time resolution of 100 fs and better. Using femtosecond transient absorption and time-resolved photoluminescence spectroscopy, we have studied the electron versus the hole dynamics in quasi-type-II hetero-nanomaterials. By choosing the pump wavelength in resonance with the respective core and shell transitions, we were able to measure the excited electron and hole dynamics selectively. Both charge carriers transfer through the interface within one picosecond, but the subsequent relaxations of the electron and hole are very distinguishable. On the basis of our measurements and analysis from the steady-state spectra, we find that the mixed core - charge transfer states and the electron transfer occur in the Marcus inverted region. The electron transfer dynamics in organic macromolecular complexes are also of interest in this dissertation. The organic capsule named octa acid is the model system studied with femtosecond laser techniques. We believe that understanding the charge carrier dynamics in nano- and supramolecular systems will pave the way to emergent optoelectronic and photovoltaic applications based on the design of functional nanoarchitectures. Moreover, exploring novel combinations, which are earth-abundant and environmentally benign, will make photoactive nanomaterials more applicable for broader use. Heterostructured assemblies (organic and inorganic) are pivotal materials in this context.
Author: Gyu-Chul Yi Publisher: Springer Science & Business Media ISBN: 3642224806 Category : Technology & Engineering Languages : en Pages : 347
Book Description
This book presents the fabrication of optoelectronic nanodevices. The structures considered are nanowires, nanorods, hybrid semiconductor nanostructures, wide bandgap nanostructures for visible light emitters and graphene. The device applications of these structures are broadly explained. The book deals also with the characterization of semiconductor nanostructures. It appeals to researchers and graduate students.
Author: Laura M. Robinson
Author: Laura M. Robinson
Author: Pradeep Bajracharya
Author: 
Author: Writam Banerjee
Author: Marcin L. Sadowski
Author: Chi-Hung Chuang
Author: Jagdeep Shah
Author: Gyu-Chul Yi
Author: Richard Andrew Adams
Author: