Metal-Semiconductor Schottky Barrier Junctions and Their Applications

Transcription

1 Metal-Semiconductor Schottky Barrier Junctions and Their Applications

2 Metal-Setniconductor Schottlcy Barrier Junctions and Their Applications Edited by B. L.Sharma Solid State Physics Laboratory Delhi, India Plenum Press.. New York and London

3 Main entry under title: Library of Congress Cataloging in Publication Data Metal-semiconductor Schottky barrier junctions and their applications. Bibliography: p. Includes index. 1. Diodes, Schottky-barrier-Addresses, essays, lectures. I. Sharma, B. L. TK S35M ' ISBN-13: e-isbn-13: : \0.\007/ Plenum Press. New York Softcover reprint of the hardcover 1 st edition 1984 A Division of Plenum Publishing Corporation 233 Spring Street, New York, N.Y All rights reserved No part of this book may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, microfilming, recording, or otherwise, without written permission from the Publisher

4 Contributors Y. Anand MIA-COM Gallium Arsenide Products, Inc., Burlington, Massachusetts R. Z. Bachrach Xerox Palo Alto Research Center, Palo Alto, California Stephen J. Fonash Engineering Science Program, The Pennsylvania State University, University Park, Pennsylvania S. C. Gupta Solid State Physics Laboratory, Delhi, India R.J. Nemanich Xerox Palo Alto Research Center, Palo Alto, California H. Preier Fraunhofer-Institut fur Physikalische Messtechnik, Freiburg, Federal Republic of Germany Dieter K. Schroder Department of Electrical and Computer Engineering, Arizona State University, Tempe, Arizona B.L. Sharma Solid State Physics Laboratory, Delhi, India M.J. Thompson Xerox Palo Alto Research Center, Palo Alto, California James A. Turner Plessey Research (Caswell) Ltd., Allen Clark Research Centre, Caswell, Towcester, Northants, England M.S. Tyagi Department of Electrical Engineering, Indian Institute of Technology, Kanpur, India v

5 Preface The present-day semiconductor technology would be inconceivable without extensive use of Schottky barrier junctions. In spite of an excellent book by Professor E.H. Rhoderick (1978) dealing with the basic principles of metalsemiconductor contacts and a few recent review articles, the need for a monograph on "Metal-Semiconductor Schottky Barrier Junctions and Their Applications" has long been felt by students, researchers, and technologists. It was in this context that the idea of publishing such a monograph by Mr. Ellis H. Rosenberg, Senior Editor, Plenum Publishing Corporation, was considered very timely. Due to the numerous and varied applications of Schottky barrier junctions, the task of bringing it out, however, looked difficult in the beginning. After discussions at various levels, it was deemed appropriate to include only those typical applications which were extremely rich in R&D and still posed many challenges so that it could be brought out in the stipulated time frame. Keeping in view the larger interest, it was also considered necessary to have the different topics of Schottky barrier junctions written by experts. This monograph is divided into eight chapters. The first chapterreviews the physics of Schottky barrier junctions, while the second deals with the interface chemistry and structure of Schottky barrier formation. Chapter 3 emphasizes the design considerations, fabrication processes, and characterization aspects of metal-silicon and metal-gallium arsenide junctions in a general way. Chapters 4-8 are concerned with specific applications. Amongst these, Chapter 4 encompasses a number of optoelectronic structures which employ not only Schottky barrier junctions but also Schottky barrier-type junctions. Chapters 5, 6, 7, and 8 deal with various theoretical and practical aspects of Schottky photodiodes, microwave Schottky diodes, MESFETs, and Schottky barrier gate CCDs, respectively. Considering the timely importance of metalamorphous silicon junctions, a chapter on such junctions and their applications is also included at the end. In a monograph of this type it is difficult to maintain the interwoven nature of the text and ensure a uniformity of presentation and notations, especially when the contributors are from different parts of the world. For this, I regret any inconvenience to those readers who prefer a textbook-type approach. vii

6 viii PREFACE Finally, I am indebted to the contributors for their self-contained contributions and to Mr. Ellis H. Rosenberg and his staff, without whose cooperation it would have been difficult to bring out this monograph in the stipulated time. B.L. SHARMA

7 Contents 1. PHYSICS OF SCHOTTKY BARRIER JUNCTIONS M.S. Tyagi 1. Introduction Origins of Barrier Height Schottky-Mott Theory of Ideal Metal-Semiconductor Contact Modifications to Schottky Theory Classifications of Metal-Semiconductor Interfaces Contacts on Reactive Interfaces Contacts with Surface States and an Insulating Interfacial Layer Contacts on Vacuum Cleaved Surfaces Measurement of Barrier Height Capacitance-Voltage Measurement Current-Voltage Measurement Photoelectric Measurement Results of Barrier Height Measurements Chemically Prepared Surfaces Vacuum Cleaved Surfaces Concluding Remarks Capacitance-Voltage Characteristics Electric Field and Potential Distribution in the Depletion Region Depletion Region Capacitance Ideal Schottky Barrier Effect of Minority Carriers Effect of Interfacial Layer Effect of Deep Traps Current-Voltage Characteristics Transport Mechanisms Diffusion and Thermionic Emission over the Barrier Tunneling through the Barrier Carrier Generation and Recombination in the Junction Depletion Region Minority Carrier Injection Forward Characteristics Reverse Characteristics Transient Behavior 53 ix

8 x 8. Low-Resistance Schottky Barrier Contacts References CONTENTS INTERFACE CHEMISTRY AND STRUCTURE OF SCHOTTKY BARRIER FORMATION R.z. Bachrach 1. Introduction.. 2. Perspectives on Schottky Barrier Formation Introduction Brief Review of Phenomenological Schottky Barrier Data 3. The Chemistry and Structure of the Interfacial Layer Synopsis of the Layer-by-Layer Evolution Some Techniques for Studying the Stages of Interface Formation. 4. Evolution of the Interfacial Layer Stage 0: The Clean Semiconductor Surface Silicon (100) and (111) Surfaces GaAs (110) and GaAs (100) Surfaces Stage 1: The Dilute Limit «1/2 Monolayer) Stage 2: Monolayer Formation-Metal Film Nucleation Stage 3: Additional Monolayers and Interdiffusion Some Specific Characteristics of the Interfacial Layers.. 5. Formation of Interface States Intrinsic Interface States Derived from the Metal and Semiconductor 5.2. Localized Defect and Impurity Related States Interface States and the Stages of Interface Formation Case Studies of the Chemistry and Structure of Schottky Barrier Formation Case Studies of Silicon Schottky Barriers AI, Ag, Cu, and Au Schottky Barriers Silicide-Silicon Interfaces Case Studies of III-V and II-VI Compound Semiconductor Schottky Barriers The Ga-AI-As System The GaAIAs Ternary System with Au Schottky Barriers InP Some II-VI Examples. 7. Summary References FABRICATION AND CHARACTERIZATION OF METAL SEMICONDUCTOR SCHOTTKY BARRIER JUNCTIONS B.L.Sharma 1. Introduction Selection of Semiconductor Materials

9 CONTENTS xi 3. Metal-Semiconductor Systems Metal-Silicon Systems Metal-GaAs Systems Multilayer Metallization Systems 4. Design Considerations 5. Fabrication Technology Surface Processing Dielectric Film Deposition 5.3. Ohmic Contact Formation 5.4. Metal Deposition Other Steps. 6. Characterization. References SCHOTTKY-BARRIER-TYPE OPTOELECTRONIC STRUCTURES Stephen J. Fonash 1. Introduction Barrier Formation in Schottky-Barrier-Type Junctions 3. Transport in Schottky-Barrier-Type Structures 3.1. MS and MIS Structures SIS Structures Schottky-Barrier-Type Optoelectronic Structures 4.1. Schottky-Barrier-Type Light-Emitting Structures Schottky-Barrier-Type Photodiodes Schottky-Barrier-Type Photovoltaic Devices MS and MIS Photovoltaic Devices SIS Photo voltaic Devices 3. Summary R~ferences SCHOTTKY BARRIER PHOTODIODES s.c. Gupta and H. Preier 1. Introduction General Parameters of Photodiodes Signal-to-Noise Ratio (SIN) Noise Equivalent Power (NEP) Detectivity (D) Normalized Detectivity (D*) Detectivity Normalized Also with Respect to the Field of View (D**) Resistance Area Product 2.7. Response Time.. 3. Selection of Materials

10 xii 3.1. Metal Systems Semiconducting Materials 4. Fabrication Technology Techniques for Evaluating Device Parameters 5.1. Current-Voltage Characteristics 5.2. Capacitance-Voltage Characteristics Photoelectric Measurements Electron Beam Induced Current Technique. 6. Applications 7. Conclusions References.. CONTENTS MICROWAVE SCHOTTKY BARRIER DIODES Y. Anand 1. Introduction Diode Design Considerations 2.1. Equivalent Circuit Frequency Conversion Basic Mixer Diode RF Parameters Conversion Loss Theory Noise-Temperature Ratio Overall Receiver Noise Figure Mixer Noise Temperature RF Impedance IF Impedance Receiver Sensitivity Doppler Shift Typical Doppler Radar System Basic Detector RF Parameters Video Resistance (Rv) Voltage Sensitivity Current Sensitivity fj Minimum Detectable Signal (MDS) Tangential Signal Sensitivity (TSS) Nominal Detectable Signal (NDS) Noise Equivalent Power (NEP) Video Bandwidth Superheterodyne vs. Single Detection Mixer Configurations Single-Ended Mixer Single-Balanced Mixer Double-Balanced Mixer Image Rejection Mixer

11 CONTENTS xiii Image Enhanced or Image Recovery Mixer Properties of Schottky Barrier Diodes Diode Theory DC Parameters Junction Capacitance Overlay Capacitance Series Resistance Figure of Merit Semiconductor Materials Epitaxial GaAs Barrier Height Lowering Fabrication Microwave Performance Mixer Diodes Detector Diodes RF Pulse and CW Burnout Introduction Factors Affecting RF Burnout Experimental Results Physical Analysis of RF Pulsed Silicon Schottky Barrier Failed Diodes Physical Analysis of RF Pulsed Millimeter GaAs Schottky Barrier Failed Diodes Electrostatic Failure of Silicon Schottky Barrier Diodes Conclusions 266 References METAL-SEMICONDUCTOR FIELD EFFECT TRANSISTORS James A. Turner 1. Introduction Small-Signal FET Theory Design Parameters of a Low-Noise Device 4. Practical Small-Signal FET Fabrication Techniques 4.1. Material Growth Techniques FET Fabrication Technology 5. GaAs Power Field Effect Transistors Principle of Power FET Operation 5.2. Thermal Impedance Power FET Technology 6. Conclusions References

12 xiv CONTENTS 8. SCHOTTKY BARRIER GATE CHARGE-COUPLED DEVICES Dieter K. Schroder 1. Introduction Schottky Gate CCDs Potential-Charge Relationships 3.1. Surface Channel CCD 3.2. Bulk Channel CCD Schottky Gate CCD. 4. Charge Storage Capacity Surface Channel CCD 4.2. Bulk Channel CCD Schottky Gate CCD. 5. Charge Transfer Charge Transfer Efficiency 5.2. Charge Transfer Mechanisms Surface Channel CCD Bulk Channel CCD Schottky Gate CCD 6. Input-Output Circuits 7. Schottky Gate Heterojunction CCDs 8. Experimental Results High-Frequency Devices 8.2. Heterojunction Devices 9. Applications Bibliography References SCHOTTKY BARRIERS ON AMORPHOUS Si AND THEIR APPLICA TIONS R.J. Nemanich and M.J. Thompson 1. Introduction 2. Properties of Amorphous Si Deposition Methods Structural Properties 2.3. Electronic Properties 2.4. Surfaces 3. The Schottky Barrier on a-si:h 3.1. Current-Voltage Measurements Capacitance Measurements 3.3 Internal Photoemission. 4. Interface Kinetics and Its Effect on the Schottky Barrier 5. Applications 5.1. Drift Mobility

13 CONTENTS 5.2. Deep Level Transient Spectroscopy 5.3. Solar Cells Thin Film Transistors 6. Concluding Remarks References Index.. xv