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2 An Elementary Approach on Solid State Devices i

3 Publishing-in-support-of, EDUCREATION PUBLISHING RZ 94, Sector - 6, Dwarka, New Delhi Shubham Vihar, Mangla, Bilaspur, Chhattisgarh Website: Copyright, Authors All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted, in any form by any means, electronic, mechanical, magnetic, optical, chemical, manual, photocopying, recording or otherwise, without the prior written consent of its writer. ISBN: Price: `INR The opinions/ contents expressed in this book are solely of the authors and do not represent the opinions/ standings/ thoughts of Educreation or the Editors. The book is released by using the services of self-publishing house. Printed in India ii

4 An Elementary Approach on Solid State Devices Mr. G. HARIKRISHNAN Assistant Professor, Department of Electronics and Communication Engineering, IMPACT College of Engineering and Applied Sciences, Bangalore, Karnataka, India. Dr. S. R. BOSELIN PRABHU Associate Professor, Department of Electronics and Communication Engineering, VSB College of Engineering Technical Campus, Coimbatore, Tamilnadu, India. EDUCREATION PUBLISHING (Since 2011) iii

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6 Preface This treatise on the subject An Elementary Approach on Solid State Devices contains comprehensive treatment of subject matter in a simple lucid and direct language. It covers the syllabus of various Indian universities. This book contains five modules which emphasis on an adaptive and systematic approach from introduction to mainstream applications It will be beneficial for students, researchers and academia s for a time bound and effective reading for easy understanding of the subject. All the five modules are saturated with much needed text supported by simple and self-explanatory figures and worked examples whenever required. This is a foundation core subject in Electronics and communication and many competitive examinations like GATE, IES etc. This book will be beneficial for preparing the subject in depth for such competitive objective and descriptive examinations. The author s thanks are due to his beloved parents and sister for extending all cooperation during preparation of the manuscript. I (Mr.G.Harikrishnan) take this opportunity to thank the management of IMPACT group of institutions for their wholehearted support especially to the founder chairman Dr.K.P.Mathulla for his inspiration and motivation. I (Dr.S.R.Boselin Prabhu) am grateful to my beloved friend Dr.E.Gajendran, Associate Professor, Sree Dattha Group of Institutions, Hyderabad because of whom I was enriched with the skill of writing books. Any suggestions for improvement of this book will be thankfully acknowledged and incorporated in the next edition Mr.G.Harikrishnan & Dr.S.R.Boselin Prabhu (Authors of the Book) v

7 Author Profiles Mr. Harikrishnan. G is working as an Assistant Professor in the Department of Electronics and Communication Engineering in IMPACT College of Engineering and Applied Sciences, Bangalore. He received his M.Tech degree in Remote Sensing and Wireless Sensor Networks from Amrita Vishwa Vidyapeeth, Ettimadai, Coimbatore. He received his B.E. in Electronics and Communication Engineering from Tamilnadu College of Engineering, Anna University Chennai. His research areas include Digital Image Processing, Software Defined Radio, Wireless Sensor Networks, CUDA, Deep Space and Hyper Spectral Image Processing. He Completed MBA in Marketing Management and highly passionate about management and business studies. Currently pursuing Ph.D. in Engineering which is in the verge of thesis submission with SCI and Scopus indexed journal publications. He has delivered several talks and workshops on philosophy of life and student centric methodological teaching learning process. Dr. Boselin Prabhu S.R. obtained his doctorate (Ph.D) from Anna University Chennai, India. He has 9 years of experience in teaching and research. He has published 163 research articles in International Journals and Conference Proceedings. He is an editorial board member, advisory board member and reviewer of 297 International Journals both Scopus and SCI Indexed. He is an elected fellow member FUAMAE, FISECE, FISRD, FUAAMP, FISQEM, SIESRP, FUACEE and FISEEE. He has attained Google scholar citations-1068 and h-index-16. He is the recipient of awards like Excellent Professional Achievement Award Winner from Society of Professional Engineers, Biography vi

8 Included in Marquis Who s who in the World (Academic Year 2015, 2016 & 2018), Dedicated Professional Engineer Award Winner from Society of Engineers & Technicians, Albert Nelson Marquis Lifetime Achievement Award Winner (2017 & 2018), Best Young Scientist from Association of Scientists, Developers and Faculties (2017), Best Young Researcher from Association of Scientists, Developers and Faculties (2017) and Bright Educator Award from International Institute of Organized Research (2018). He has written 12 books and two monographs for students. vii

9 This Book Shall Be Dedicated to Our Student Friends viii

10 Contents Module 1 Energy bands and charge carriers in semiconductors: energy bands- metals- semiconductors and insulators- direct and indirect semiconductors- charge carriers in semiconductors: electrons and holes- intrinsic and extrinsic material- n-material and p-materialcarrier concentration: fermi level- EHPs- temperature dependanceconductivity and mobility- drift and resistance- effect of temperature and doping on mobility- hall effect. Module 2 Diffusion of carriers- derivation of diffusion constant (D)- Einstein relation- continuity equation- p-n junctions: contact potentialequilibrium fermi levels- space charge at junctions- current components at a junction: majority and minority carrier currentszener and avalanche breakdown- capacitance of p-n junctions. Module 3 p-n junction diodes: volt-ampere characteristics- switching timerectifier action -Zener diodes: volt-ampere characteristics- Tunnel diodes: tunneling phenomena- volt-ampere characteristics- Varactor diodes- Photo diodes: detection principle- light emitting diodes. Module 4 Bipolar junction transistors: npn and pnp transistor action- open circuited transistor- biasing in active region- majority and minority carrier distribution- terminal currents- amplification and switching- and ß gain factors- emitter efficiency - schottky transistorsphoto transistors. Module 5 Field effect transistors: operation- pinch off and saturation- pinch off voltage- gate control- volt-ampere characteristics- MOSFETS: ix

11 n MOS and p MOS: comparison- enhancement and depletion types- control of threshold voltage- MOS capacitance. x

12 Table of Contents Sr. Title Page Module I 1 Bonding Forces and Energy Bands in Solids 1. Energy Bands 3 2. Metals, Semiconductors, And Insulators 5 3. Direct and Indirect Semiconductors 6 4. Variation of Energy Bands with Alloy 7 Composition 5. Charge Carriers in Semiconductors 8 6. Electrons and Holes 9 7. Effective Mass Intrinsic Material Extrinsic Material Carrier Concentrations Temperature Dependence of Carrier 22 Concentrations 12. Compensation and Space Charge Neutrality Drift of Carriers In Electric and Magnetic Fields Effects of Temperature and Doping on Mobility High-Field Effects The Hall Effect 34 Module II 38 Excess Carriers in Semiconductors 1. Carrier Lifetime Direct Recombination of Electrons and Holes Indirect Recombination Steady State Carrier Generation; Quasi-Fermi 42 Levels 5. Diffusion of Carriers Diffusion and Recombination; The Continuity 51 Equation xi

13 7. Steady State Carrier Injection; Diffusion Length P-N Junctions-Equilibrium Conditions The Contact Potential Equilibrium Fermi Levels Space Charge at A Junction Forward and Reverse Biased Conditions Qualitative Description of Current Flow at A 63 Junction 14. Carrier Injection 67 Module III 70 Reverse Breakdown in PN Junctions 1. Zener Breakdown Avalanche Breakdown Breakdown Diodes Transient and A-C Conditions Reverse Recovery Transient Switching Diodes Capacitance of P-N Junctions The Varactor Diode Metal Semiconductor Junctions Optoelectronic Devices Optical Absorption Luminescence Solar Cells Light-Emitting Diodes Lasers 96 Module IV 99 The Ideal MOS Capacitor 1. Threshold Voltage Tunnel Diodes P-N-P-N Diodes Semiconductor controlled Rectifier (SCR) Insulated-Gate Bipolar Transistor (IGBT) Mosfet Metal Oxide FET Depletion-Mode MOSFET Enhancement-Mode MOSFET Transconductance Control of Threshold Voltage Basic Principles of CMOS 131 xii

14 Module V 134 Fundamentals of BJT Operation 1. Amplification with BJTs Minority Carrier Distributions and Terminal 139 Currents 3. Current Transfer Ratio Switching Base Narrowing Avalanche Breakdown Base Resistance and Emitter Crowding The Junction FET (JFET) Currents-Voltage Characteristics 161 References 164 xiii

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16 Mr.G.Harikrishnan Module I Bonding Forces and Energy Bands in Solids The basic difference between the case of an electron in a solid and that of an electron in an isolated atom is that in the solid the electron has a range, or band, of available energies. The discrete energy levels of the isolated atom spread into bands of energies in the solid because in the solid the wave functions of electrons in neighboring atoms overlap, and an electron is not necessarily localized at a particular atom. The interaction of electrons in neighboring atoms of a solid serves the very important function of holding the crystal together. For example, alkali halides such as NaCl are typified by ionic bonding. Fig.1 An example of ionic bonding in NaCl In the NaCl lattice, each Na atom is surrounded by six nearest neighbor CI atoms, and vice versa. Four of the nearest neighbors are evident in the two-dimensional representation shown in Fig.1. The electronic structure of Na (Z = 11) is [Ne] 3s1, and CI (Z = 1

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