HIGHER PHYSICS Electricity
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Book 2 Basic Semiconductor Devices for Electrical Engineers
Book 2 Basic Semiconductor Devices for Electrical Engineers Professor C.R. Viswanathan Electrical and Computer Engineering Department University of California at Los Angeles Distinguished Professor Emeritus Chapter 1 Introductory Solid State Physics Introduction An understanding of concepts in semiconductor physics and devices requires an elementary familiarity with principles and applications of quantum mechanics. Up to the end of nineteenth century all the investigations in physics were conducted using Newton’s Laws of motion and this branch of physics was called classical physics. The physicists at that time held the opinion that all physical phenomena can be explained using classical physics. However, as more and more sophisticated experimental techniques were developed and experiments on atomic size particles were studied, interesting and unexpected results which could not be interpreted using classical physics were observed. Physicists were looking for new physical theories to explain the observed experimental results. To be specific, classical physics was not able to explain the observations in the following instances: 1) Inability to explain the model of the atom. 2) Inability to explain why the light emitted by atoms in an electric discharge tube contains sharp spectral lines characteristic of each element. 3) Inability to provide a theory for the observed properties in thermal radiation i.e., heat energy radiated by a hot body. 4) Inability to explain the experimental results obtained in photoelectric emission of electrons from solids. Early physicists Planck (thermal radiation), Einstein (photoelectric emission), Bohr (model of the atom) and few others made some hypothetical and bold assumptions to make their models predict the experimental results. -
Condensed Matter Physics
Condensed Matter Physics Crystal Structure Basic crystal structure Crystal: an infinite repeated pattern of identical groups of atoms, consisting of a basis and a lattice Basis: a group of atoms which forms the crystal structure Lattice: the three-dimensional set of points on which the basis is attached to form the crystal Primitive cell: the cell of the smallest volume which can be translated to map out all the points on the lattice. The primitive cell is not unique for a given crystal. There is always exactly one lattice point per primitive cell Conventional cell: a more convenient unit which also translates to map out the entire lattice, often a cube Wigner-Seitz primitive cell: this is a special form of the primitive cell constructed by connecting a given lattice point to all its neighbours, then drawing new lines as the mid-points of these lines 1 Lattice point group: a collection of symmetry operations which map the lattice back onto itself, such as translation, reflection, and rotation Miller indices Miller indices are an indexing system for defining planes and directions in a crystal. The method for defining them is as follows: Find the intercepts of the plane with the axes in terms of lattice constants Take the reciprocal of each intercept, then reduce the ratio to the smallest possible integer ratio A particular plane is denoted A set of planes equivalent by symmetry is denoted The direction perpendicular to is denoted by The reciprocal lattice If we have a repeating lattice we can represent the electron density by a periodic function, which we can write as a Fourier series: Where the factors of ensure that has the required periodic relation . -
Lecture 3 Electron and Hole Transport in Semiconductors Review
Lecture 3 Electron and Hole Transport in Semiconductors In this lecture you will learn: • How electrons and holes move in semiconductors • Thermal motion of electrons and holes • Electric current via drift • Electric current via diffusion • Semiconductor resistors ECE 315 – Spring 2005 – Farhan Rana – Cornell University Review: Electrons and Holes in Semiconductors holes + electrons + + As Donor A Silicon crystal lattice + impurity + As atoms + ● There are two types of mobile charges in semiconductors: electrons and holes In an intrinsic (or undoped) semiconductor electron density equals hole density ● Semiconductors can be doped in two ways: N-doping: to increase the electron density P-doping: to increase the hole density ECE 315 – Spring 2005 – Farhan Rana – Cornell University 1 Thermal Motion of Electrons and Holes In thermal equilibrium carriers (i.e. electrons or holes) are not standing still but are moving around in the crystal lattice because of their thermal energy The root-mean-square velocity of electrons can be found by equating their kinetic energy to the thermal energy: 1 1 m v 2 KT 2 n th 2 KT vth mn In pure Silicon at room temperature: 7 vth ~ 10 cm s Brownian Motion ECE 315 – Spring 2005 – Farhan Rana – Cornell University Thermal Motion of Electrons and Holes In thermal equilibrium carriers (i.e. electrons or holes) are not standing still but are moving around in the crystal lattice and undergoing collisions with: • vibrating Silicon atoms • with other electrons and holes • with dopant atoms (donors or acceptors) and -
A Note on the Electrochemical Nature of the Thermoelectric Power
Eur. Phys. J. Plus (2016) 131:76 THE EUROPEAN DOI 10.1140/epjp/i2016-16076-8 PHYSICAL JOURNAL PLUS Regular Article A note on the electrochemical nature of the thermoelectric power Y. Apertet1,a, H. Ouerdane2,3, C. Goupil4, and Ph. Lecoeur5 1 Lyc´ee Jacques Pr´evert, F-27500 Pont-Audemer, France 2 Russian Quantum Center, 100 Novaya Street, Skolkovo, Moscow region 143025, Russian Federation 3 UFR Langues Vivantes Etrang`eres, Universit´e de Caen Normandie, Esplanade de la Paix 14032 Caen, France 4 Laboratoire Interdisciplinaire des Energies de Demain (LIED), UMR 8236 Universit´e Paris Diderot, CNRS, 5 Rue Thomas Mann, 75013 Paris, France 5 Institut d’Electronique Fondamentale, Universit´e Paris-Sud, CNRS, UMR 8622, F-91405 Orsay, France Received: 16 November 2015 / Revised: 21 February 2016 Published online: 4 April 2016 – c Societ`a Italiana di Fisica / Springer-Verlag 2016 Abstract. While thermoelectric transport theory is well established and widely applied, it is not always clear in the literature whether the Seebeck coefficient, which is a measure of the strength of the mutual interaction between electric charge transport and heat transport, is to be related to the gradient of the system’s chemical potential or to the gradient of its electrochemical potential. The present article aims to clarify the thermodynamic definition of the thermoelectric coupling. First, we recall how the Seebeck coefficient is experimentally determined. We then turn to the analysis of the relationship between the thermoelectric power and the relevant potentials in the thermoelectric system: As the definitions of the chemical and electrochemical potentials are clarified, we show that, with a proper consideration of each potential, one may derive the Seebeck coefficient of a non-degenerate semiconductor without the need to introduce a contact potential as seen sometimes in the literature. -
Digital Electronics Part II – Electronics, Devices and Circuits Dr
Digital Electronics Part II – Electronics, Devices and Circuits Dr. I. J. Wassell Introduction • In the coming lectures we will consider how logic gates can be built using electronic circuits • First, basic concepts concerning electrical circuits and components will be introduced • This will enable the analysis of linear circuits, i.e., one where superposition applies: – If an input x1(t) gives an output y1(t), and input x2(t) gives an output y2(t), then input [x1(t)+x2(t)] gives an output [y1(t)+y2(t)] 1 Introduction • However, logic circuits are non-linear, consequently we will introduce a graphical technique for analysing such circuits • Semiconductor materials, junction diodes and field effect transistors (FET) will be introduced • The construction of an NMOS inverter from an n-channel (FET) will then be described • Finally, CMOS logic built using FETs will then be presented Basic Electricity • An electric current is produced when charged particles e.g., electrons in metals, move in a definite direction • A battery acts as an ‘electron pump’ and forces the free electrons in the metal to drift through the metal wire in the direction from its -ve terminal toward its +ve terminal + Flow of electrons - 2 Basic Electricity • Actually, before electrons were discovered it was imagined that the flow of current was due to positively charged particles flowing out of +ve toward –ve battery terminal • Indeed, the positive direction of current flow is still defined in this way! • The unit of charge is the Coulomb (C). One Coulomb is equivalent to the charge carried by 6.25*1018 electrons (since one electron has a charge of 1.6*10-19 Coulombs). -
Theoretical Analysis on Transient Photon-Generated Voltage in Polymer Based Organic Devices
Electronic Supplementary Material (ESI) for Physical Chemistry Chemical Physics This journal is © The Owner Societies 2012 Supporting Information (SI) Theoretical Analysis on transient photon-generated voltage in polymer based organic devices. 5 To further confirm the conclusion in the manuscript, a theoretical model, simultaneously taking into account the possible excitons and carrier processes in the active polymer layer after photo excitation and the interaction of different polar species formed in different phases has been developed. The interphasic and 10 intraphasic interactions have to be considered in the studies of Device No.1, 2 and 3. For Device No.2 and Device No.3, since one pristine polymer is used for these devices, intraphasic interaction will dominate the processes. However, as polymer blend is used in Device 1, both interphasic and intraphasic interactions will exist. The details are discussed as belows. 15 We present a time-dependent device model, describing the dynamical processes of both excitons induced by light illumination and charge carriers created from the exciton dissociation in pristine polymer layer and blend layer. Then we calculate the transient photovoltage (TPV) in single-layer organic photovoltaic cells. With the 20 model, the theoretical TPV has been determined and analyzed with the experimental results for further verifying the conclusion of this work. Considering (1) the laser pulse transmits into the polymer layer through the ITO side; (2) the absorption length of polymer layer is much less than the thickness of polymer 25 layer in our devices, for example, for Device No. 3, the absorption length is around 100 nm and thickness of P3HT layer is around 240nm and (3) the exciton lifetime is ultra-short with a value around 500 ps, excitons will have very little population near interface of polymer layer/Al which will thus be ignored in the model. -
Effect of Drift and Diffusion Processes in the Change of the Current Direction in a Fet Transistor
EFFECT OF DRIFT AND DIFFUSION PROCESSES IN THE CHANGE OF THE CURRENT DIRECTION IN A FET TRANSISTOR By OSCAR VICENTE HUERTA GONZALEZ A Dissertation submitted to the program in Electronics, in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE WITH SPECIALTY IN ELECTRONICS At the National Institute por Astrophysics, Optics and Electronics (INAOE) Tonantzintla, Puebla February, 2014 Supervised by: DR. EDMUNDO A. GUTIERREZ DOMINGUEZ INAOE ©INAOE 2014 All rights reserved The author hereby grants to INAOE permission to reproduce and to distribute copies of this thesis document in whole or in part. DEDICATION There are several people which I would like to dedicate this work. First of all, to my parents, Margarita González Pantoja and Vicente Huerta Escudero for the love and support they have given me. They are my role models because of the hard work and sacrifices they have made so that my brothers and me could set high goals and achieve them. To my brothers Edgard de Jesus and Jairo Arturo, we have shared so many things, and helped each other on our short lives. I would also like to thank Lizbeth Robles, one special person in my life, thanks for continuously supporting and encouraging me to give my best. And thanks to every member of my family and friends for their support. They have contributed to who I am now. ACKNOWLEDGEMENTS I would like to thank the National Institute for Astrophysics, Optics and Electronics (INAOE) for all the facilities that contributed to my successful graduate studies. To Consejo Nacional de Ciencia y Tecnologia (CONACYT) for the economic support. -
1 the Drift Current and Diffusion Current
the Drift Current and Diffusion Current There are two types of current through a semiconducting material – one is drift current and the other is diffusion current. The mechanism of drift current is similar to the flow of charge in a conductor. In case of conductor when a voltage is applied across the material, the electrons are drawn to the positive end. Similar is the case in semiconductor. However, the movement of the charge carriers may be erratic path due to collisions with other atoms, ions and carriers. So, the net result is a drift of carriers to the positive end. In semiconducting material, when a heavy concentration of carrier is introduced to some region, the heavy concentrations of carriers distribute themselves evenly through the material by the process of diffusion. It should be remembered that there is no source of energy as required for drift current. When an electric field is applied across the crystal, every charge carrier experiences a force due to the electric field and hence it will be accelerated in the direction of force. This results in drifting of the charge carriers in the direction of force will cause a net flow of electric current through the crystal. Drift current The flow of charge carriers, which is due to the applied voltage or electric field is called drift current. In a semiconductor, there are two types of charge carriers, they are electrons and holes. When the voltage is applied to a semiconductor, the free electrons move towards the positive terminal of a battery and holes move towards the negative terminal of a battery.