The Effects of Electron Temperature in Terahertz Quantum Cascade Laser Predictions PDF Download
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Languages : en
Pages : 9
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Book Description
Quantum cascade lasers (QCL's) employ the mid- and far-infrared intersubband radiative transitions available in semiconducting heterostructures. Through the precise design and construction of these heterostructures the laser characteristics and output frequencies can be controlled. When fabricated, QCL's offer a lightweight and portable alternative to traditional laser systems which emit in this frequency range. The successful operation of these devices strongly depends on the effects of electron transport. Studies have been conducted on the mechanisms involved in electron transport and a prediction code for QCL simulation and design has been completed. The implemented approach utilized a three period simulation of the laser active region. All of the wavefunctions within the simulation were included in a self-consistent rate equation model. This model employed all relevant types of scattering mechanisms within three periods. Additionally, an energy balance equation was studied to determine the temperature of electron distributions separately from the lattice temperature. This equation included the influence of both electron-LO phonon and electron-electron scattering. The effect of different modelling parameters within QCL electron temperature predictions will be presented along with a description of the complete QCL prediction code.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 9
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Book Description
Quantum cascade lasers (QCL's) employ the mid- and far-infrared intersubband radiative transitions available in semiconducting heterostructures. Through the precise design and construction of these heterostructures the laser characteristics and output frequencies can be controlled. When fabricated, QCL's offer a lightweight and portable alternative to traditional laser systems which emit in this frequency range. The successful operation of these devices strongly depends on the effects of electron transport. Studies have been conducted on the mechanisms involved in electron transport and a prediction code for QCL simulation and design has been completed. The implemented approach utilized a three period simulation of the laser active region. All of the wavefunctions within the simulation were included in a self-consistent rate equation model. This model employed all relevant types of scattering mechanisms within three periods. Additionally, an energy balance equation was studied to determine the temperature of electron distributions separately from the lattice temperature. This equation included the influence of both electron-LO phonon and electron-electron scattering. The effect of different modelling parameters within QCL electron temperature predictions will be presented along with a description of the complete QCL prediction code.
Author: Benjamin Adams Burnett
Publisher:
ISBN:
Category :
Languages : en
Pages : 223
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Book Description
The portion of the electromagnetic spectrum between roughly 300 GHz and 10 THz is nicknamed the "THz Gap" because of the enormous difficulty encountered by researchers to devise practical sources covering it. Still, the quantum cascade laser (QCL) has emerged over recent years as the most promising approach to a practical source in the 1-5 THz range. First developed in the higher-frequency mid-IR, where they are now widely available, QCLs were later extended to the THz where a host of greater design challenges awaited. Lasing in QCLs is based on intersubband optical transitions in semiconductor quantum wells, the energy of which can be chosen by design ("bandstructure engineering"). However, simply building a THz optical transition is insufficient; a good design must also produce significant population inversion by the applied cascading electron current, and this requires deep understanding of the transport physics. So far, no THz QCL has operated above the temperature of 200 K, even though the reasons prohibiting high temperature operation are well known. The goal of this Thesis is to put novel ideas for high-temperature operation of THz QCL active regions through rigorous theoretical testing. The central enabling development is a density-matrix-based model of transport and optical properties tailored for use in QCLs, which is general enough that widely varying design concepts can be tested using the same core principles. Importantly, by simulating QCLs more generally, fewer a priori assumptions are required on part of the researcher, allowing for the true physics to emerge on its own. It will be shown that this gives rise to new and useful insights that will help to guide the experimental efforts towards realization of these devices. One specific application is a quantum dot cascade laser (QDCL), a highly ambitious approach in which the electrons cascade through a series of quantum dots rather than wells. Benefits are expected due to the suppression of nonradiative scattering, brought about by the discrete spectrum of electronic states. However, this in turn leads to a highly different physics of transport and effects that are not well understood, even in the case of perfect materials. This work will show that while the benefits are clear, naive scaling of existing QCL designs to the quantum dot limit will not work. An alternative strategy is given based on a revised understanding of the nature of transport, and is put to a test of practicality in which the effects of quantum dot size inhomogeneity are estimated. Another application is to the already existing method of THz difference frequency generation in mid-IR QCLs, which occurs via a difference-frequency susceptibility $\chi^{(2)}$ in the active region itself. For this purpose, the model is extended to enable a coherent and nonperturbative calculation of optical nonlinearities. First, the generality of the method is displayed through the emergence of exotic nonlinear effects, including electromagnetically-induced transparency, in mock quantum-well systems. Then, the modeling concepts are applied to the real devices, where two new and important mechanisms contributing to $\chi^{(2)}$ are identified. Most importantly, it is predicted that the QCL acts as an extremely fast photodetector of itself, giving rise to a current response to the mid-IR beatnote that provides a better path forward to the generation of frequencies below ~2 THz. Finally, the fundamentals of density matrix transport theory for QCLs are revisited to develop a model for conventional THz QCL designs eliminating the usual phenomenological treatment of scattering. The new theory is fully developed from first principles, and in particular sheds light on the effects of scattering-induced electron localization. The versatility of the model is demonstrated by successful simulation of varying active region designs.
Author: Lianhe Li
Publisher: Frontiers Media SA
ISBN: 2889760200
Category : Science
Languages : en
Pages : 120
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Book Description
Author: Dan Botez
Publisher: Cambridge University Press
ISBN: 1108427936
Category : Science
Languages : en
Pages : 551
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Book Description
A state-of-the-art overview of this rapidly expanding field, featuring fundamental theory, practical applications, and real-life examples.
Author: Seyed Ghasem Razavipour
Publisher:
ISBN:
Category :
Languages : en
Pages : 129
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Book Description
Quantum cascade laser (QCL), as a unipolar semiconductor laser based on intersubband transitions in quantum wells, covers a large portion of the Mid and Far Infrared electromagnetic spectrum. The frequency of the optical transition can be determined by engineering the layer sequence of the heterostructure. The focus of this work is on Terahertz (THz) frequency range (frequency of 1 - 10 THz and photon energy of ~ 4 - 40 meV), which is lacking of high power, coherent, and efficient narrowband radiation sources. THz QCL, demonstrated in 2002, as a perfect candidate of coherent THz source, is still suffering from the empirical operating temperature limiting factor of T [ap] h̳[omega]/kB, which allows this source to work only under a cryogenic system. Most of high performance THz QCLs, including the world record design which lased up to ~ 200 K, are based on a resonant phonon (RP) scheme, whose population inversion is always less than 50%. The indirectly-pumped (IDP) QCL, nicely implemented in MIR frequency, starts to be a good candidate to overcome the aforementioned limiting factor of RP-QCL. A rate equation (RE) formalism, which includes both coherent and incoherent transport process, will be introduced to model the carrier transport of all presented structures in this thesis. The second order tunneling which employed the intrasubband roughness and impurity scattering, was implemented in our model to nicely predict the behavior of the QCL designs. This model, which is easy to implement and fast to calculate, could help us to engineer the electron wavefunctions of the structure with optimization tools. We developed a new design scheme which employs the phonon scattering mechanism for both injecting carrier to the upper lasing state and extracting carrier from lower lasing state. Since there is no injection/extraction state to be in resonance with lasing states, this simple design scheme does not suffer from broadening due to the tunneling. Finally, three different THz IDP-QCLs, based on phonon-photon-phonon (3P) scheme were designed, grown, fabricated, and characterized. The performance of those structures in terms of operating temperature, threshold current density, maximum current density, output optical power, lasing frequency, differential resistance at threshold, intermediate resonant current before threshold, and kBT/h̳[omega] factor will be compared. We could improve the kBT/h̳[omega] factor of the 3P-QCL design from 0.9 in first iteration to 1.3 and the output optical power of the structure from 0.9 mW in first design to 3.4 mW. The performance of the structure in terms of intermediate resonant current and the change in differential resistance at threshold was improved.
Author: Muhammad Mustafa Hussain
Publisher: John Wiley & Sons
ISBN: 352734358X
Category : Technology & Engineering
Languages : en
Pages : 284
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Book Description
Brings novel insights to a vibrant research area with high application potential?covering materials, physics, architecture, and integration aspects of future generation CMOS electronics technology Over the last four decades we have seen tremendous growth in semiconductor electronics. This growth has been fueled by the matured complementary metal oxide semiconductor (CMOS) technology. This comprehensive book captures the novel device options in CMOS technology that can be realized using non-silicon semiconductors. It discusses germanium, III-V materials, carbon nanotubes and graphene as semiconducting materials for three-dimensional field-effect transistors. It also covers non-conventional materials such as nanowires and nanotubes. Additionally, nanoelectromechanical switches-based mechanical relays and wide bandgap semiconductor-based terahertz electronics are reviewed as essential add-on electronics for enhanced communication and computational capabilities. Advanced Nanoelectronics: Post-Silicon Materials and Devices begins with a discussion of the future of CMOS. It continues with comprehensive chapter coverage of: nanowire field effect transistors; two-dimensional materials for electronic applications; the challenges and breakthroughs of the integration of germanium into modern CMOS; carbon nanotube logic technology; tunnel field effect transistors; energy efficient computing with negative capacitance; spin-based devices for logic, memory and non-Boolean architectures; and terahertz properties and applications of GaN. -Puts forward novel approaches for future, state-of-the-art, nanoelectronic devices -Discusses emerging materials and architectures such as alternate channel material like germanium, gallium nitride, 1D nanowires/tubes, 2D graphene, and other dichalcogenide materials and ferroelectrics -Examines new physics such as spintronics, negative capacitance, quantum computing, and 3D-IC technology -Brings together the latest developments in the field for easy reference -Enables academic and R&D researchers in semiconductors to "think outside the box" and explore beyond silica An important resource for future generation CMOS electronics technology, Advanced Nanoelectronics: Post-Silicon Materials and Devices will appeal to materials scientists, semiconductor physicists, semiconductor industry, and electrical engineers.
Author: Paul Harrison
Publisher: John Wiley & Sons
ISBN: 1118923367
Category : Science
Languages : en
Pages : 626
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Book Description
Quantum Wells, Wires and Dots provides all the essential information, both theoretical and computational, to develop an understanding of the electronic, optical and transport properties of these semiconductor nanostructures. The book will lead the reader through comprehensive explanations and mathematical derivations to the point where they can design semiconductor nanostructures with the required electronic and optical properties for exploitation in these technologies. This fully revised and updated 4th edition features new sections that incorporate modern techniques and extensive new material including: Properties of non-parabolic energy bands Matrix solutions of the Poisson and Schrödinger equations Critical thickness of strained materials Carrier scattering by interface roughness, alloy disorder and impurities Density matrix transport modelling Thermal modelling Written by well-known authors in the field of semiconductor nanostructures and quantum optoelectronics, this user-friendly guide is presented in a lucid style with easy to follow steps, illustrative examples and questions and computational problems in each chapter to help the reader build solid foundations of understanding to a level where they can initiate their own theoretical investigations. Suitable for postgraduate students of semiconductor and condensed matter physics, the book is essential to all those researching in academic and industrial laboratories worldwide. Instructors can contact the authors directly (
[email protected] /
[email protected]) for Solutions to the problems.
Author: Matthew Michael Suttinger
Publisher:
ISBN:
Category :
Languages : en
Pages : 47
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Book Description
Quantum Cascade Lasers are a novel source of coherent infrared light, unique in their tunability over the mid-infrared and terahertz range of frequencies. Advances in bandgap engineering and semiconductor processing techniques in recent years have led to the development of highly efficient quantum cascade lasers capable of room temperature operation. Recent work has demonstrated power scaling with broad area quantum cascade lasers by increasing active region width beyond the standard ~10 [micrometer]. Taking into account thermal effects caused by driving a device with electrical power, an experimentally fitted model is developed to predict the optical power output in both pulsed and continuous operation with varying device geometry and minor changes to quantum cascade laser active region design. The effects of the characteristic temperatures of threshold current density and slope efficiency, active region geometry, and doping, on output power are studied in the model. The model is then used to refine the active region design for increased power out in continuous operation for a broad area design. Upon testing the new design, new thermal effects on rollover current density are observed. The model is then refined to reflect the new findings and more accurately predict output power characteristics.
Author: Chun Wang Ivan Chan
Publisher:
ISBN:
Category :
Languages : en
Pages : 251
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Book Description
Terahertz Quantum Cascade Lasers (THz QCLs) are arguably the most promising technology today for the compact, efficient generation of THz radiation. Their main limitation is that they require cryogenic cooling, which dominates their ownership cost. Therefore, achieving room-temperature operation is essential for the widespread adoption of THz QCLs. This thesis analyzes the limitations of THz QCL maximum lasing temperature (Tmax) and proposes solutions. THz QCL Tmax is hypothesized to be limited by a fundamental trade-off between gain oscillator strength ful and upper-level lifetime [Tau]. This so-called "ful[Tau] tradeoff" is shown to explain the failure of designs which target [Tau] alone. A solution is proposed in the form of highly diagonal (low ful) active region design coupled with increased doping. Experimental results indicate the strategy to be promising, but heavily doped designs are shown to suffer band-bending effects which may deteriorate performance. In order to treat these band-bending effects, which are typically neglected in previous THz QCL designs, a fast transport simulation tool is developed. Scattering integrals are simplified using the assumption of thermalized sub bands. Results comparable to ensemble Monte Carlo are achieved at a fraction of the computational expense. Carrier leakages to continuum states are also investigated, although they are found to have little effect. Other work in this thesis includes the optimization of double-metal THz waveguides to enable Tmax ~ 200 K, a current world record. Furthermore, laser designs to investigate the leakages of carriers to high-energy subbands and continuum states were fabricated and tested; such parasitic leakages are suggested to be small. Finally, the design of gain media for applications is examined, notably the development of 4.7 THz gain media for OI line detection in astrophysics, and the development of broadband heterogeneous gain media for THz comb generation.
Author: Shuo Tang
Publisher: CRC Press
ISBN: 1315354101
Category : Technology & Engineering
Languages : en
Pages : 236
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Book Description
This introductory, yet in-depth, book explains the physical principles of electronic imaging and sensing and provides the reader with the information necessary to understand the design, operation, and practical applications of contemporary electronic imaging and sensing systems. The text has strong practical focus and contains examples of biomedical applications of optical electronic imaging and sensing. Each chapter draws upon the authors’ extensive research, teaching, and industrial experience and provides a useful resource for undergraduate and graduate students, as well as a convenient reference for scientists and engineers working in the field of electronic imaging and sensing.
