Microwave Semiconductor Devices

Microwave Semiconductor Devices

SITESH KUMAR ROYChief Investigator, Formerly Professor and Head

Institute of Radiophysics and ElectronicsCalcutta University

MONOJIT MITRADepartment of Electronics and Telecommunication Engineering

Bengal Engineering College (Deemed University), Howrah

Delhi-110 0922017

MICROWAVE SEMICONDUCTOR DEVICESSitesh Kumar Roy and Monojit Mitra

© 2003 by PHI Learning Private Limited, Delhi. All rights reserved. No part of this book may be reproduced in any form, by mimeograph or any other means, without permission in writing from the publisher.

ISBN-978-81-203-2418-3

The export rights of this book are vested solely with the publisher.

Published by Asoke K. Ghosh, PHI Learning Private Limited, Rimjhim House, 111, Patparganj Industrial Estate, Delhi-110092 and Printed by Mohan Makhijani at Rekha Printers Private Limited, New Delhi-110020.

v

��������

Preface xi

Chapter 1 Microwave and Millimeter Wave Devices 1–51.0 Introduction 11.1 Microwave Regions and Band Designation 41.2 Advantage of Microwave and Millimeter Wave 5

Chapter 2 Physics of Semiconductor Devices 6–472.0 Introduction 62.1 Semiconductor Materials 7

2.1.1 Element semiconductor 72.1.2 Compound semiconductor 7

2.2 Classification of Semiconductors 82.2.1 Intrinsic carrier concentration 92.2.2 Extrinsic semiconductors 112.2.3 Non-degenerate semiconductors 122.2.4 Degenerate semiconductors 13

2.3 Carrier Mobility 142.4 Electrical Conductivity 152.5 Effects of Temperature and Doping on Mobility 182.6 Carrier Diffusion 192.7 Einstein’s Relationship 192.8 Lifetime of Minority Carriers 202.9 Continuity Equation 212.10 Behaviour of Charged Particles at the Interface 22

2.10.1 Metal-n-type semiconductor with Wm > Ws 222.10.2 Metal-n-type semiconductor with Wm < Ws 232.10.3 Metal-p-type semiconductor with Wm > Ws 242.10.4 Metal-p-type semiconductor with Wm < Ws 242.10.5 Metal Intrinsic semiconductor interface 252.10.6 Potential distribution and space change width at metal

semiconductor interface 25

vi Contents

2.11 Semiconductor Junction 262.11.1 Unbiased p-n junction 272.11.2 Biased p-n junction 292.11.3 Volt-amp (V–I) characteristics of p-n junction 302.11.4 Junction capacitances 352.11.5 Effects of high field on charge carriers in semiconductors 372.11.6 Impact ionization and creation of e-h pairs at high field 382.11.7 Theory of exponential field dependence of ionization rate 392.11.8 Charge multiplication and avalanche breakdown of junctions 402.11.9 Zener breakdown 442.11.10 Resistance of a p-n junction diode 45

References 45Suggested Readings 45Problems 45

Chapter 3 Microwave IMPATT Devices 48–853.0 Introduction 483.1 Saturation of Drift Velocity 483.2 Impact Ionization, Carrier Multiplication and Junction Breakdown 513.3 IMPATT Structures and Doping Profiles 543.4 Basic Principle of Generation of Microwaves in IMPATT Diodes 543.5 Small Signal Analysis Based on Analytical Approximation 583.6 DC to Microwave Conversion Efficiency 593.7 Effect of Mobile Space Charge 603.8 Double Avalanche Region (DAR) IMPATT Diode and Cancellation of Space

Charge Effect 623.9 Low-High-Low Diodes for Reduction of Space Charge Effect and Constriction

of Avalanche Zone 623.10 High Frequency Consideration 633.11 Fabrication of IMPATT Diodes 643.12 GaAs and InP IMPATT Diodes 643.13 Noise in IMPATT Diode 663.14 Thermal Limitation and Heat Sink 663.15 Millimeter Wave IMPATT Packaging 663.16 Millimeter Wave IMPATT Devices and Sources 673.17 CW mm Wave IMPATT Diodes 703.18 Doping Density and Drift Layer Widths of mm Wave IMPATT against

Frequency 703.19 Fabrication of mm Wave IMPATT Diodes 72

3.19.1 Diffusion 723.19.2 Ion implantation 733.19.3 Molecular beam epitaxy 733.19.4 Metallization 743.19.5 Thinning 743.19.6 Photolithography and mesa etching 743.19.7 Package and bonding of mm wave IMPATT chip 74

Contents vii

3.20 mm Wave IMPATT Oscillator Circuits and Performances 743.21 CW Millimeter Wave Oscillators 753.22 Heat Sink of IMPATT Oscillator 773.23 Bias Filter of the IMPATT Oscillator 773.24 Output Characteristics of a mm Wave IMPATT Source 783.25 Pulse mm Wave IMPATT Devices 803.26 Fabrication of Pulsed IMPATT Diodes 813.27 Frequency Chirp of Pulsed IMPATT Oscillators 813.28 Discussions 82References 83Suggested Readings 84Problems 85

Chapter 4 TRAPATT Diodes 86–984.0 Introduction 864.1 Basic Principle of TRAPATT Operation 874.2 Avalanche Shock Front Propagation 874.3 Velocity of the Avalanche Shock Front 894.4 Extractions of Trapped Plasma and Recovery of the Electric Field 904.5 Triggering Voltage and TRAPATT Circuit 924.6 TRAPATT Oscillation Condition and Oscillation Frequency 934.7 Frequency of Oscillation of a TRAPATT Diode 974.8 Performance of TRAPATT Oscillators 97References 97Suggested Readings 98Problems 98

Chapter 5 BARITT Diodes 99–1065.0 Introduction 995.1 BARITT Structure and DC Field Profiles 995.2 Small Signal Microwave Profiles of a BARITT Diode 1025.3 Large Signal Operation of BARITT Diode and Optimum Frequency of

Oscillation 1035.4 Discussion 105References 106Suggested Readings 106Problems 106

Chapter 6 Transfer Electron Devices (Gunn Diode) 107–1256.0 Introduction 1076.1 The Transferred Electron Mechanism 1076.2 Domain Formation 1106.3 Modes of Operation of Gunn Diode 112

6.3.1 Transit-time domain mode 1126.3.2 Delayed domain mode 1136.3.3 Quenched domain mode 1136.3.4 Limited space-charge accumulation (LSA) mode 113

viii Contents

6.4 Criterion for Classifying the Modes of Operation 1166.5 Mode Chart for Transferred Electron Devices 1176.6 Fabrication of Gunn Diode 1176.7 Typical Characteristics 1186.8 Application of Gunn Diode 1196.9 Gunn Oscillator Circuits 1196.10 Gunn Diode Amplifier 1216.11 Disadvantage of Gunn Diode 1226.12 InP Gunn Diode 122References 123Suggested Readings 124Problems 124

Chapter 7 Tunnel Diode 126–1397.0 Introduction 1267.1 Tunnelling Process 1267.2 Principle of Tunnel Diode 1287.3 Volt-Amp Characteristics of a Tunnel Diode 1307.4 Material and Construction of Tunnel Diode 1317.5 Tunnel Diode Equivalent Circuit of Oscillator 1327.6 Tunnel Diode Oscillator Using Cavity 1337.7 Tunnel Diode Amplifier with Circulator 1347.8 Tunnel Diode Switch 1367.9 Resonant Tunnelling Diode (RTD) 137References 138Suggested Readings 139Problems 139

Chapter 8 Schottky Barrier Diodes 140 –1468.0 Introduction 1408.1 Theory 1408.2 Surface States in Practical Schottky Barrier Diodes 1448.3 Structure of Schottky Diodes 144References 146Suggested Readings 146Problems 146

Chapter 9 Microwave Bipolar Transistors 147–1569.0 Introduction 1479.1 Physical Structure 1479.2 Principle of Operation 1489.3 Performance Parameter 1499.4 Power Frequency Limitations 1499.5 Applications 152

Contents ix

9.6 Heterojunction Bipolar Transistors (HBTs) 1529.6.1 Structure of heterojunction transistors 1529.6.2 Application of heterojunction bipolar transistor (HBT) 154

References 155Suggested Readings 155Problems 155

Chapter 10 Metal Semiconductor Field Effect Transistors (MESFETs) 157–177

10.0 Introduction 15710.1 Structure of MESFET 15710.2 Device Fabrication and Packaging 15810.3 Materials for MESFETs 16010.4 Principle of Operation of MESFET 16110.5 Small Signal Equivalent Circuit 16310.6 Dual Gate MESFET 16910.7 MESFET Oscillators 17110.8 MESFET Amplifiers 173References 175Suggested Readings 176Problems 176

Chapter 11 High Electron Mobility Transistor (Modulation Doped Field Effect Transistor) 178–185

11.0 Introduction 17811.1 Heterojunction and 2-DEG 17911.2 Device Structure and Fabrication 18111.3 HEMT Characteristics 18111.4 Recent Development of HEMT 18311.5 Conclusion 184References 184Suggested Readings 184Problems 184

Appendix 187–190

Index 191–192

Microwaves have been used extensively since the Second World War when the sources werebased on vacuum devices. Microwaves (3–30 GHz) are presently playing a vital role in landbased and satellite based communication and radars and have wide civilian and defenceapplications. In recent years, due to availability and emergence of semiconductor millimeterwave sources, millimeter waves (30–300 GHz) are finding wider application in ground andsatellite communication, radars and missile guidance systems. This wide spectrum ofapplication is making the millimeter wave system development one of the most advancedtechnology of radio science, specially in view of the ever increasing demand ofcommunication and saturation of microwave frequency range with increasing number ofchannels. Millimeter wave semiconductor devices are presently under intensive investigationby various researchers all over the world although Sir J.C. Bose successfully generatedelectromagnetic waves of wavelength 6 mm and frequency 50 GHz in Calcutta as early as1896.

This book is intended to provide a foundation to understand the physics andoperational principle of microwave and millimeter wave semiconductor devices. Thesedevices are making a revolutionary change in the field of communication and radartechnology and will have important emerging applications in the twenty-first century.

The book deals with IMPATTs, Gunns, FETs, HEMTs etc., which are discussed ingreater detail to provide fundamental knowledge to students, engineers and scientists.Various three-terminal and two-terminal devices in the microwave and millimeter wave fieldbased on silicon and other Gr III-V semiconductors are discussed in the book.

The book will serve as a textbook for undergraduate electronics engineering studentsand a reference book for professional engineers and physicists.

We are indebted to the Centre of Advanced Study in Radio Physics and Electronics,University of Calcutta, for providing the facilities to write this book and also to BengalEngineering College, Howrah, for necessary help to us. We are thankful to the co-investigatorsDr. D. Ghoshal, Dr. N. Majumder, Sri B. Maity, Sri N.C. Mondal and Sri T.K. Pal.

Finally we thank Mr. Santanu Ghosh and Mr. Subhadeep Seal for typesetting, drawingfigures and illustrations of the manuscript.

Sitesh Kumar RoyMonojit Mitra

�����

xxx x i

�

�������� �� � ��������� ��� ����

1.0 INTRODUCTIONMicrowaves cover the wavelength range of 10–1 cm, and millimeter waves cover the wavelength 1 cm–1 mm, corresponding to the high frequency electromagnetic oscillation rangingfrom 3 GHz–300 GHz. They have significant application in communication since they act ascarriers of information in analog and digital form. Devices, which generate microwaves andmillimeter waves, are essential for satellite and line of sight communication for audio andvideo signals as also for digital data communications. Moreover, microwaves are very usefulfor radars since they can penetrate through fog and cloud.

Millimeter waves are emerging very fast as highly suitable for carrying large numberof channels of audio, video and data since the frequency is about 10 times more thanmicrowaves and the microwave frequency-range as carriers of information is getting saturatedfor communication. Small antennas and sharp beams characterize millimeter wave systems.Millimeter wave devices are also being used in missile technology for defence applications.

The early generations of microwaves during the Second World War were vacuumdevices, viz. Klystrons, Magnetrons and Travelling wave tubes, which depended on themotion of electrons in vacuum for various configurations of electric and magnetic fields. Thesetubes were heavy and bulky and required high voltage for their operation and occupied largespace.

The invention of transistors led to almost complete replacement of vacuum triodes andpentodes in the audio and radio frequency range. The integration of a large number oftransistors in very large-scale integrated circuits led to solid-state replacement on computerswitching circuits, which were originally based on vacuum triodes and pentodes.Simultaneously, solid-state replacement of microwaves and millimeter waves started in the1960s. Among these devices, Gunn diodes, IMPATT diodes, Bipolar transistors, MetalSemiconductor Field Effect Transistors (MESFET), and High Electron Mobility Transistors(HEMT) have emerged as highly suitable generators of microwaves and millimeter waves.IMPATT (IMPact ionization Avalanche Transit Time) covers the frequency range of3–300 GHz, and is now the most powerful solid-state source covering the entire frequencyspectrum of microwaves and millimeter waves. IMPATTs are based on p-n junctions of Ge,Si, GaAs and InP. Gunn diode covers the frequency range up to 100 GHz and providessufficient low noise microwave power for communication. It is a bulk device based on n-GaAsor n-InP. Bipolar transistor, and MESFET operate at microwave frequency-range as ordinary

�������

2 Microwave Semiconductor Devices

bipolar transistor and MESFET with technological refinements. HEMT depends on formationof a two-dimensional electrons gas formed at the heterojunction of AlGaAs and GaAs whenelectrons move with very high speed under the gate electrode and generate oscillation up to60 GHz. These semiconductor devices are basically small and reliable and they require lowvoltage for their operation. The oscillators and amplifiers based on these devices are findingwide application in satellite and terrestrial communications. Since computers worldwide arebeing linked through communication lines and satellites, microwave and millimeter wavedevices will play a key role as microwave and millimeter wave sources in the expandingworld of information technology.

A summary of energy band, carrier distribution, transport properties, and devicetechnology including different methods for junction formation are presented emphasizing onthe three most important semiconductors, germanium (Ge), silicon (Si), and gallium arsenide(GaAs). This will help to understand the device characteristics.

A detailed discussion is given on IMPATT devices, which have emerged as verypowerful solid-state source of microwave, millimeter wave and submillimeter wave power.IMPATT is the acronym for IMPact Avalanche Transit Time and is basically a p-n junctiondiode of appropriate doping profile reversed biased to breakdown. Due to vast frequencyrange of operation and large power output IMPATT devices would find increasingapplications in the 21st Century. Due to the importance of IMPATT devices in both microwaveand millimeter wave range a special emphasis is given to it in this book. The physics ofmicrowave and millimeter semiconductor devices, principle of operation, applications ofmicrowave IMPATT devices and sources are therefore discussed in detail.

TRAPATT (TRApped Plasma Avalanche Triggered Transit) which is a solid-statemicrowave device with very high dc to microwave conversion efficiency and capable ofproducing high microwave power under pulsed mode operation is also discussed. Itsfrequency is restricted to lower microwave frequency range.

BARITT diodes (BARrier Injection Transit Time) is normally a p+np+ or metal–n–metaljunction and is equivalent to a pair of diodes, connected back to back. BARITT can generatemicrowave power with very low noise but operates at lower microwave frequency.

Transfer electron devices, popularly called Gunn diodes, which depend for its operationon negative differential mobility in certain Gr-III & V semiconductors which arise due to thetransfer of electrons from low to high valley conduction bands in n-type GaAs and n-type InPis discussed. These devices are bulk semiconductor devices based on band properties ofGr-III & V semiconductors. They are suitable as microwave and millimeter wave sources upto 100 GHz and are having large number of applications in microwave and millimeter wavesystems.

Other types of junction diodes useful for microwaves and millimeter waves are tunneldiodes, backward diodes and Schottky diodes. Tunnel diodes are based on tunnelling ofmajority carrier across p-n junction. They have high speed and are used as pump sources inparametric amplifiers.

Metal semiconductor Schottky barrier diode is used as detector of microwave power.Under normal operating conditions it exhibits a square low response. The lower 1/f noise,better reliability and low burn out of this diode have made it more advantageous than thepoint contact diode.

High frequency bipolar as well as heterojunction transistors are also discussed. Mostof the bipolar devices are fabricated from silicon and can give appreciable power up to20 GHz.

Microwave and Millimeter Wave Devices 3

MESFET is a field effect transistor having metal semiconductor junction, where thedepletion layer is controlled by gate electric field. Its efficiency and frequency range is higherthan those of a bipolar transistor. MESFET has emerged as a very important source ofmicrowave of lower millimeter wave frequencies.

High Electron Mobility Transistor (HEMT), which has a selectively doped GaAs–AlGaAs heterojunction structure is discussed. HEMT is characterized by higher speed andhigher frequency operation than MESFET. HEMT has a great promise and is a suitable devicefor VLSI chips, space communication and high-speed super computers.

Figure 1.1 shows the output power available at different frequencies from differentdevices.

Pow

er o

utpu

t (m

W)

Frequency (GHz)

CW GaAs IMPATT

GaAs FETs

GaAs GUNN

HEMT

InP GUNN

CW Si IMPATT

20 W20000

100008000

6000

4000

2000

1000800

600

400

200

10080

60

40

20

1010 20 40 60

10 W

1 W

Figure 1.1 State of the art for microwave and millimeter wave solid state sources.

Microwave Semiconductor Devices

Publisher : PHI Learning ISBN : 9788120324183 Author : Roy And Mitra

Type the URL : http://www.kopykitab.com/product/10259

Get this eBook

25%OFF