Heterostructure and Quantum Well Physics
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Quantum Well Devices: Applications of the PIAB
Quantum Well Devices: Applications of the PIAB. H2A Real World Friday What is a semiconductor? no e- Conduction Band Empty e levels a few e- Empty e levels lots of e- Empty e levels Filled e levels Filled e levels Filled e levels Insulator Semiconductor Metal Electrons in the conduction band of semiconductors like Si or GaAs can move about freely. Conduction band a few e- Eg = hν Energy Bandgap in Valence band Filled e levels Semiconductors We can get electrons into the conduction band by either thermal excitation or light excitation (photons). Solar cells use semiconductors to convert photons to electrons. A "quantum well" structure made from AlGaAs-GaAs-AlGaAs creates a potential well for conduction electrons. 10-20 nm! A conduction electron that get trapped in a quantum well acts like a PIAB. A conduction electron that get trapped in a quantum well acts like a PIAB. Quantum Wells are used to make Laser Diodes Quantum Well Laser Diodes Quantum Wells are used to make Laser Diodes Quantum Well Laser Diodes Multiple Quantum Wells work even better. Multiple Quantum Well Laser Diodes Multiple Quantum Wells work even better. Multiple Quantum Well LEDs Multiple Quantum Wells work even better. Multiple Quantum Well Laser Diodes Multiple Quantum Wells also are used to make high efficiency Solar Cells. Quantum Well Solar Cells Multiple Quantum Wells also are used to make high efficiency Solar Cells. The most common approach to high efficiency photovoltaic power conversion is to partition the solar spectrum into separate bands and each absorbed by a cell specially tailored for that spectral band. -
Federico Capasso “Physics by Design: Engineering Our Way out of the Thz Gap” Peter H
6 IEEE TRANSACTIONS ON TERAHERTZ SCIENCE AND TECHNOLOGY, VOL. 3, NO. 1, JANUARY 2013 Terahertz Pioneer: Federico Capasso “Physics by Design: Engineering Our Way Out of the THz Gap” Peter H. Siegel, Fellow, IEEE EDERICO CAPASSO1credits his father, an economist F and business man, for nourishing his early interest in science, and his mother for making sure he stuck it out, despite some tough moments. However, he confesses his real attraction to science came from a well read children’s book—Our Friend the Atom [1], which he received at the age of 7, and recalls fondly to this day. I read it myself, but it did not do me nearly as much good as it seems to have done for Federico! Capasso grew up in Rome, Italy, and appropriately studied Latin and Greek in his pre-university days. He recalls that his father wisely insisted that he and his sister become fluent in English at an early age, noting that this would be a more im- portant opportunity builder in later years. In the 1950s and early 1960s, Capasso remembers that for his family of friends at least, physics was the king of sciences in Italy. There was a strong push into nuclear energy, and Italy had a revered first son in En- rico Fermi. When Capasso enrolled at University of Rome in FREDERICO CAPASSO 1969, it was with the intent of becoming a nuclear physicist. The first two years were extremely difficult. University of exams, lack of grade inflation and rigorous course load, had Rome had very high standards—there were at least three faculty Capasso rethinking his career choice after two years. -
Dephasing in an Electronic Mach-Zehnder Interferometer,” Phys
Dephasing and Quantum Noise in an electronic Mach-Zehnder Interferometer Dissertation zur Erlangung des Doktorgrades der Naturwissenschaften (Dr. rer. nat.) der Fakultät für Physik der Universität Regensburg vorgelegt von Andreas Helzel aus Kelheim Dezember 2012 ii Promotionsgesuch eingereicht am: 22.11.2012 Die Arbeit wurde angeleitet von: Prof. Dr. Christoph Strunk Prüfungsausschuss: Prof. Dr. G. Bali (Vorsitzender) Prof. Dr. Ch. Strunk (1. Gutachter) Dr. F. Pierre (2. Gutachter) Prof. Dr. F. Gießibl (weiterer Prüfer) iii In Gedenken an Maria Höpfl. Sie war die erste Taxifahrerin von Kelheim und wurde 100 Jahre alt. Contents 1. Introduction1 2. Basics 5 2.1. The two dimensional electron gas....................5 2.2. The quantum Hall effect - Quantized Landau levels...........8 2.3. Transport in the quantum Hall regime.................. 10 2.3.1. Quantum Hall edge states and Landauer-Büttiker formalism.. 10 2.3.2. Compressible and incompressible strips............. 14 2.3.3. Luttinger liquid in the QH regime at filling factor 2....... 16 2.4. Non-equilibrium fluctuations of a QPC.................. 24 2.5. Aharonov-Bohm Interferometry..................... 28 2.6. The electronic Mach-Zehnder interferometer............... 30 3. Measurement techniques 37 3.1. Cryostat and devices........................... 37 3.2. Measurement approach.......................... 39 4. Sample fabrication and characterization 43 4.1. Fabrication................................ 43 4.1.1. Material.............................. 43 4.1.2. Lithography............................ 44 4.1.3. Gold air bridges.......................... 45 4.1.4. Sample Design.......................... 46 4.2. Characterization.............................. 47 4.2.1. Filling factor........................... 47 4.2.2. Quantum point contacts..................... 49 4.2.3. Gate setting............................ 50 5. Characteristics of a MZI 51 5.1. -
DESIGN and FABRICATION of Gan-BASED HETEROJUNCTION BIPOLAR TRANSISTORS
DESIGN AND FABRICATION OF GaN-BASED HETEROJUNCTION BIPOLAR TRANSISTORS By KYU-PIL LEE A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2003 In his heart a man plans his course, But, the LORD determines his steps. Proverbs 16:9 ACKNOWLEDGMENTS First and foremost, I would like to express great appreciation with all my heart to Professor Pearton and Professor Ren for their expert advice, guidance, and instruction throughout the research. I also give special thanks to members of my committee (Professor Abernathy, Professor Norton, and Professor Singh) for their professional input and support. Additional special thanks are reserved for the people of our research group (Kwang-hyun, Kelly, Ben, Jihyun, and Risarbh) for their assistance, care, and friendship. I am very grateful to past group members (Sirichai, Pil-yeon, David, Donald and Bee). 1 also give my thanks to P. Mathis for her endless help and kindness; and to Mr. Santiago who is network assistant in the Chemical Engineering Department, because of his great help with my simulation. I also thank my discussion partners about material growth technologies, Dr. B. Gila, Dr. M. Overberg, Jerry and Dr. Kang-Nyung Lee. I would like to give my thanks to my friends (especially Kyung-hoon, Young-woo, Se-jin, Byeng-sung, Yong-wook, and Hyeng-jin). Even when they were very busy, they always helped my research work without hesitation. I cannot forget Samsung's vice president Dr. Jong-woo Park’s devoted help, and the steadfast support from Samsung Electronics. -
Based Vertical Double Heterojunction Bipolar Transistors with High Current Amplification
COMMUNICATION Heterojunction Bipolar Transistor www.advelectronicmat.de 2D Material-Based Vertical Double Heterojunction Bipolar Transistors with High Current Amplification Geonyeop Lee, Stephen J. Pearton, Fan Ren, and Jihyun Kim* been applied to various types of semicon- The heterojunction bipolar transistor (HBT) differs from the classical homo- ductor devices, such as lasers, solar cells, junction bipolar junction transistor in that each emitter-base-collector layer high electron mobility transistors, and het- [3–6] is composed of a different semiconductor material. 2D material (2DM)- erojunction bipolar transistors (HBTs). Notably, with a bipolar junction transistor, based heterojunctions have attracted attention because of their wide range which is a three-terminal transistor fabri- of fundamental physical and electrical properties. Moreover, strain-free cated by connecting two P–N homojunc- heterostructures formed by van der Waals interaction allows true bandgap tion diodes, there is a trade-off between engineering regardless of the lattice constant mismatch. These characteristics the current gain and high-frequency ability [3,7] make it possible to fabricate high-performance heterojunction devices such because of these problems. In sharp contrast, HBTs realized using the hetero- as HBTs, which have been difficult to implement in conventional epitaxy. structure can avoid these trade-offs and Herein, NPN double HBTs (DHBTs) are constructed from vertically stacked improve device performance.[8] HBTs, due 2DMs (n-MoS2/p-WSe2/n-MoS2) using dry transfer technique. The forma- to their high power efficiency, uniformity tion of the two P–N junctions, base-emitter, and base-collector junctions, of threshold voltage, and low 1/f noise in DHBTs, was experimentally observed. -
Quantum Dot and Electron Acceptor Nano-Heterojunction For
www.nature.com/scientificreports OPEN Quantum dot and electron acceptor nano‑heterojunction for photo‑induced capacitive charge‑transfer Onuralp Karatum1, Guncem Ozgun Eren2, Rustamzhon Melikov1, Asim Onal3, Cleva W. Ow‑Yang4,5, Mehmet Sahin6 & Sedat Nizamoglu1,2,3* Capacitive charge transfer at the electrode/electrolyte interface is a biocompatible mechanism for the stimulation of neurons. Although quantum dots showed their potential for photostimulation device architectures, dominant photoelectrochemical charge transfer combined with heavy‑metal content in such architectures hinders their safe use. In this study, we demonstrate heavy‑metal‑free quantum dot‑based nano‑heterojunction devices that generate capacitive photoresponse. For that, we formed a novel form of nano‑heterojunctions using type‑II InP/ZnO/ZnS core/shell/shell quantum dot as the donor and a fullerene derivative of PCBM as the electron acceptor. The reduced electron–hole wavefunction overlap of 0.52 due to type‑II band alignment of the quantum dot and the passivation of the trap states indicated by the high photoluminescence quantum yield of 70% led to the domination of photoinduced capacitive charge transfer at an optimum donor–acceptor ratio. This study paves the way toward safe and efcient nanoengineered quantum dot‑based next‑generation photostimulation devices. Neural interfaces that can supply electrical current to the cells and tissues play a central role in the understanding of the nervous system. Proper design and engineering of such biointerfaces enables the extracellular modulation of the neural activity, which leads to possible treatments of neurological diseases like retinal degeneration, hearing loss, diabetes, Parkinson and Alzheimer1–3. Light-activated interfaces provide a wireless and non-genetic way to modulate neurons with high spatiotemporal resolution, which make them a promising alternative to wired and surgically more invasive electrical stimulation electrodes4,5. -
17 Band Diagrams of Heterostructures
Herbert Kroemer (1928) 17 Band diagrams of heterostructures 17.1 Band diagram lineups In a semiconductor heterostructure, two different semiconductors are brought into physical contact. In practice, different semiconductors are “brought into contact” by epitaxially growing one semiconductor on top of another semiconductor. To date, the fabrication of heterostructures by epitaxial growth is the cleanest and most reproducible method available. The properties of such heterostructures are of critical importance for many heterostructure devices including field- effect transistors, bipolar transistors, light-emitting diodes and lasers. Before discussing the lineups of conduction and valence bands at semiconductor interfaces in detail, we classify heterostructures according to the alignment of the bands of the two semiconductors. Three different alignments of the conduction and valence bands and of the forbidden gap are shown in Fig. 17.1. Figure 17.1(a) shows the most common alignment which will be referred to as the straddled alignment or “Type I” alignment. The most widely studied heterostructure, that is the GaAs / AlxGa1– xAs heterostructure, exhibits this straddled band alignment (see, for example, Casey and Panish, 1978; Sharma and Purohit, 1974; Milnes and Feucht, 1972). Figure 17.1(b) shows the staggered lineup. In this alignment, the steps in the valence and conduction band go in the same direction. The staggered band alignment occurs for a wide composition range in the GaxIn1–xAs / GaAsySb1–y material system (Chang and Esaki, 1980). The most extreme band alignment is the broken gap alignment shown in Fig. 17.1(c). This alignment occurs in the InAs / GaSb material system (Sakaki et al., 1977). -
Heterojunction Quantum Dot Solar Cells
Heterojunction Quantum Dot Solar Cells by Navid Mohammad Sadeghi Jahed A thesis presented to the University of Waterloo in fulfillment of the thesis requirement for the degree of Doctor of Philosophy in Electrical and Computer Engineering Waterloo, Ontario, Canada, 2016 © Navid Mohammad Sadeghi Jahed 2016 I hereby declare that I am the sole author of this thesis. This is a true copy of the thesis, including any required final revisions, as accepted by my examiners. I understand that my thesis may be made electronically available to the public. ii Abstract The advent of new materials and application of nanotechnology has opened an alternative avenue for fabrication of advanced solar cell devices. Before application of nanotechnology can become a reality in the photovoltaic industry, a number of advances must be accomplished in terms of reducing material and process cost. This thesis explores the development and fabrication of new materials and processes, and employs them in the fabrication of heterojunction quantum dot (QD) solar cells in a cost effective approach. In this research work, an air stable, highly conductive (ρ = 2.94 × 10-4 Ω.cm) and transparent (≥85% in visible range) aluminum doped zinc oxide (AZO) thin film was developed using radio frequency (RF) sputtering technique at low deposition temperature of 250 °C. The developed AZO film possesses one of the lowest reported resistivity AZO films using this technique. The effect of deposition parameters on electrical, optical and structural properties of the film was investigated. Wide band gap semiconductor zinc oxide (ZnO) films were also developed using the same technique to be used as photo electrode in the device structure. -
Band Alignment and Graded Heterostructures
Band Alignment and Graded Heterostructures Guofu Niu Auburn University Outline • Concept of electron affinity • Types of heterojunction band alignment • Band alignment in strained SiGe/Si • Cusps and Notches at heterojunction • Graded bandgap • Impact of doping on equilibrium band diagram in graded heterostructures Reference • My own SiGe book – more on npn SiGe HBT base grading • The proc. Of the IEEE review paper by Nobel physics winner Herb Kromer – part of this lecture material came from that paper • The book chapter of Prof. Schubert of RPI – book can be downloaded online from docstoc.com • http://edu.ioffe.ru/register/?doc=pti80en/alfer_e n.tex - by Alfreov, who shared the noble physics prize with Kroemer for heterostructure laser work 3 Band alignment • So far I have intentionally avoided the issue of band alignment at heterojunction interface • We have simply focused on – ni^2 change due to bandgap change for abrupt junction – Ec or Ev gradient produced by Ge grading • We have seen in our Sdevice simulation that the final band diagrams actually depend on doping – A Ec gradient favorable for electron transport is obtained for forward Ge grading in p-type (npn HBT) – A Ev gradient favorable for hole transport is obtained for forward Ge grading in n-type (pnp HBT) Electron Affinity – rough picture • Neglect interface between vacuum and semiconductor, vacuum level is drawn to be position independent • The energy needed to move an electron from Ec to vacuum level is called electron affinity. 5 Electron Affinity Model • The electron affinity model is the oldest model invoked to calculate the band offsets in semiconductor heterostructures (Anderson, 1962). -
Modeling Multiple Quantum Well and Superlattice Solar Cells
Natural Resources, 2013, 4, 235-245 235 http://dx.doi.org/10.4236/nr.2013.43030 Published Online July 2013 (http://www.scirp.org/journal/nr) Modeling Multiple Quantum Well and Superlattice Solar Cells Carlos I. Cabrera1, Julio C. Rimada2, Maykel Courel2,3, Luis Hernandez4,5, James P. Connolly6, Agustín Enciso4, David A. Contreras-Solorio4 1Department of Physics, University of Pinar del Río, Pinar del Río, Cuba; 2Solar Cell Laboratory, Institute of Materials Science and Technology (IMRE), University of Havana, Havana, Cuba; 3Higher School in Physics and Mathematics, National Polytechnic Insti- tute, Mexico City, Mexico; 4Academic Unit of Physics, Autonomous University of Zacatecas, Zacatecas, México; 5Faculty of Phys- ics, University of Havana, La Habana, Cuba; 6Nanophotonics Technology Center, Universidad Politécnica de Valencia, Valencia, Spain. Email: [email protected] Received January 23rd, 2013; revised May 14th, 2013; accepted May 27th, 2013 Copyright © 2013 Carlos I. Cabrera et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. ABSTRACT The inability of a single-gap solar cell to absorb energies less than the band-gap energy is one of the intrinsic loss mechanisms which limit the conversion efficiency in photovoltaic devices. New approaches to “ultra-high” efficiency solar cells include devices such as multiple quantum wells (QW) and superlattices (SL) systems in the intrinsic region of a p-i-n cell of wider band-gap energy (barrier or host) semiconductor. These configurations are intended to extend the absorption band beyond the single gap host cell semiconductor. -
Heterojunction Engineering for Next Generation Hybrid II-VI Materials
City University of New York (CUNY) CUNY Academic Works All Dissertations, Theses, and Capstone Projects Dissertations, Theses, and Capstone Projects 9-2017 Heterojunction Engineering for Next Generation Hybrid II-VI Materials Thor Garcia The Graduate Center, City University of New York How does access to this work benefit ou?y Let us know! More information about this work at: https://academicworks.cuny.edu/gc_etds/2385 Discover additional works at: https://academicworks.cuny.edu This work is made publicly available by the City University of New York (CUNY). Contact: [email protected] HETEROJUNCTION ENGINEERING FOR NEXT GENERATION HYBRID II-VI MATERIALS by THOR AXTMANN GARCIA A dissertation submitted to the Graduate Faculty in chemistry in partial fulfillment of the requirements for the degree of Doctor of Philosophy, The City University of New York 2017 © 2017 THOR AXTMANN GARCIA All Rights Reserved ii Heterojunction Engineering for Next Generation Hybrid II-VI Materials by Thor Axtmann Garcia This manuscript has been read and accepted for the Graduate Faculty in chemistry in satisfaction of the dissertation requirement for the degree of Doctor of Philosophy. Date Professor Maria C. Tamargo Chair of Examining Committee Date Professor Brian R. Gibney Executive Officer Supervisory Committee: Professor Aidong Shen Professor Igor L. Kuskovsky Professor Glen Kowach THE CITY UNIVERSITY OF NEW YORK iii ABSTRACT Heterojunction Engineering for Next Generation Hybrid II-VI Materials by Thor Axtmann Garcia Advisor: Professor Maria C. Tamargo Molecular Beam Epitaxy(MBE) is a versatile thin film growth technique with monolayer control of crystallization. The flexibility and precision afforded by the technique allows for unique control of interfaces and electronic structure of the films grown. -
Chapter 2 Quantum Theory
Chapter 2 - Quantum Theory At the end of this chapter – the class will: Have basic concepts of quantum physical phenomena and a rudimentary working knowledge of quantum physics Have some familiarity with quantum mechanics and its application to atomic theory Quantization of energy; energy levels Quantum states, quantum number Implication on band theory Chapter 2 Outline Basic concept of quantization Origin of quantum theory and key quantum phenomena Quantum mechanics Example and application to atomic theory Concept introduction The quantum car Imagine you drive a car. You turn on engine and it immediately moves at 10 m/hr. You step on the gas pedal and it does nothing. You step on it harder and suddenly, the car moves at 40 m/hr. You step on the brake. It does nothing until you flatten the brake with all your might, and it suddenly drops back to 10 m/hr. What’s going on? Continuous vs. Quantization Consider a billiard ball. It requires accuracy and precision. You have a cue stick. Assume for simplicity that there is no friction loss. How fast can you make the ball move using the cue stick? How much kinetic energy can you give to the ball? The Newtonian mechanics answer is: • any value, as much as energy as you can deliver. The ball can be made moving with 1.000 joule, or 3.1415926535 or 0.551 … joule. Supposed it is moving with 1-joule energy, you can give it an extra 0.24563166 joule by hitting it with the cue stick by that amount of energy.