SEMICONDUCTORS AND SEMIMETALS VOLUME 19 Deep Levels, GaAs, Alloys, Photochemistry This page intentionally left blank SEMICONDUCTORS AND SEMIMETALS Edited by R. K. WILLARDSON WILLARDSON CONSULTING SPOKANE, WASHINGTON ALBERT C. BEER BATTELLE COLUMBUS LABORATORIES COLUMBUS, onio VOLUME 19 Deep Levels, GaAs, Alloys, Photochemistry 1983 ACADEMIC PRESS A Subsidiary of ffarcourt Brace Jovanovich, Publishers New York London Paris San Diego San Francisco Sdo Paul0 Sydney Tokyo Toronto COPYRIGHT @ 1983, BY ACADEMIPCRE SS, INC. ALL RIGHTS RESERVED. NO PART OF THIS PUBLICATION MAY BE REPRODUCED OR TRANSMITTED IN ANY FORM OR BY ANY MEANS, ELECTRONIC OR MECHANICAL, INCLUDING PHOTOCOPY, RECORDING, OR ANY INFORMATION STORAGE AND RETRIEVAL SYSTEM, WITHOUT PERMISSION IN WRITING FROM THE PUBLISHER. ACADEMIC PRESS, INC. 111 Fifth Avenue, New York, New York 10003 United Kingdom Edition published by ACADEMIC PRESS, INC. (LONDON) LTD. 24/28 Oval Road, London NWl IDX Library of Congress Cataloging in Publication Data (Revised for volume 19) Main entry under title: Semiconductors and semimetals. Includes bibliographical refercnccs and indexes. Contents: v. 1-2. Physics of Ill-V compounds-. v. 3. Optical properties of Ill-V compounds- [etc.] -- v. 19. Deep levels, GaAs, alloys, photochemistry. 1. Semiconductors--Collected works. 2. Semimetals-- Collected works. 1. Willardson, Robert K. 11. Beer, Albert C. QC610.9.S47 537.6'22 65-26048 ISBN 0-12-7521 19-4 PRINTED IN THE UNITED STATES OF AMERICA 83 84 85 86 9 8 1 6 5 4 3 2 1 Contents LISTO F CONTRIBUTOR.S . . . . . . . . . . . . vii PREFACE. . . . . . . . . . . . . . . . ix Chapter 1 Deep Levels in Wide Band-Gap Semiconductors 111-V G . F . Neurnark and K . Kosai I . Introduction . . . . . . . . . . . . . . 1 I1 . Experimental Characterization of Deep Levels . . . . . . . 7 111 . Observation and Intercomparison of Deep Levels . Results for GaAs and GaP . . . . . . . . . . . 2 0 IV . Theory of Recombination . . . . . . . . . . . 3 0 V . Analysis of Optical Cross Sections . . . . . . . . . 52 References . . . . . . . . . . . . . . 6 5 Chapter 2 The Electrical and Photoelectronic Properties of Semi-Insulating GaAs David C . Look List of Symbols . . . . . . . . . . . . . 76 I . Introduction . . . . . . . . . . . . . . 7 7 . Hall Effect and Magnetoresistance . . . . . . . . . 77 I1 111 . Thermal Equilibrium Processes . . . . . . . . . . 8 6 IV . Nonequilibrium Processes . . . . . . . . . . . 9 6 V . Comparison of Techniques . . . . . . . . . . . 121 Appendix A . Charge Transport Theory . . . . . . . . 12 7 Appendix B . Semiconductor Statistics . . . . . . . . 14 8 Appendix C . Derivation of TSC and PITS Equations . . . . . 16 2 References . . . . . . . . . . . . . . 16 7 Chapter 3 Associated Solution Model for Ga-In-Sb and Hg-Cd-Te R . F . Brebrick. Ching-Hua Su. and Pok-Kai Liao List of Symbols . . . . . . . . . . . . . 17 2 I . Introduction . . . . . . . . . . . . . . 17 3 I1 . Thermodynamic Equations for the Liquidus Surface of (A,-.B,)C(s) . . 178 111 . Solution Thermodynamics . . . . . . . . . . . 18 1 IV . Associated Solution Model for the Liquid Phase . . . . . . 186 V vi CONTENTS V . Ga-In-SbTernary . . . . . . . . . . . . 19 7 VI . Hg-Cd-TeTernary . . . . . . . . . . . . 214 VII.Sununary . . . . . . . . . . . . . . 23 0 AppendixA . . . . . . . . . . . . . . 231 Appendix B . . . . . . . . . . . . . . 234 AppendixC . . . . . . . . . . . . . . 24 2 References . . . . . . . . . . . . . . 251 Chapter 4 Photoelectrochemistry of Semiconductors Yu . Yu. Gurevich and Yu . V . Pleskov List of Symbols . . . . . . . . . . . . . 256 I . Introduction . . . . . . . . . . . . . . 257 I1 . General Concepts of the Electrochemistry of Semiconductors . . . . 259 . III The Theory of Processes Caused by Photoexcitation of Semiconductors . . . . . . . . . . . . 273 IV . Photocorrosion and Its Prevention . . . . . . . . . 282 V . Light-Sensitive Etching of Semiconductors . . . . . . . 294 . Processes Caused by Photoexcitation of Reactants in the Solution . . . 30 3 VI VII . Selected Problems in the Photoelectrochemistry of Semiconductors . . . 31 0 VIII . Conclusion: Problems and Prospects . . . . . . . . . 323 References . . . . . . . . . . . . . . 324 INDEX . . . . . . . . . . . . . . . . 32 9 CONTENTOSF PREVIOUSV OLUMES . . . . . . . . . . 339 List of Contributors Numbers in parentheses indicate the pages on which the authors’ contributions begin R. F. BREBRICKM, aterials Science and Metallurgy Program, College of Engineering, Marquette University, Milwaukee, Wisconsin 53233 (171) Yu. YA. GUREVICHIn,s titute of Electrochemistry, Academy of Sciences of the USSR, 117071 Moscow, USSR (255) K. KOSAI,P’ hilips Laboratories, Briarcliff Manor, New York 10510 (1) POK-KAIL IAO,M aterials Science and Metallurgy Program, College of Engineering, Marquette University, Milwaukee, Wisconsin 53233 (171) DAVIDC . LOOK,U niversity Research Center, Wright State University, Dayton, Ohio 45435 (75) G. F. NEUMARPKhi,l ips Laboratories, Briarcliff Manor, New York 10510 (1) Yu. V. PLESKOVIn, stitute of Electrochemistry, Academy of Sciences of the USSR, 117071 Moscow, USSR (255) CHING-HUAS u, Materials Science and Metallurgy Program, College of Engineering, Marquette University, Milwaukee, Wisconsin 53233 (171) I Present address: Santa Barbara Research Center, Goieta, California 931 17. vii This page intentionally left blank Preface This treatise reflects the rapid growth in the field of semiconductors and semimetals. Chapters 1 and 2 of the present volume are concerned with deep levels in wide band-gap III-V compounds and the measurement techniques used to characterize such levels. These chapters provide a background for the next volume, which will address the use of semi- insulating GaAs in digital and microwave integrated circuits (ICs) as well as providing valuable insight into methods of improving solar cells, lasers, and light-emitting diodes (LEDs). Chapter 3 in the present volume is concerned with thermodynamic modeling to improve Hg-Cd-Te phase diagrams applicable to the infrared detector arrays discussed in Volume 18 of this treatise. Chapter 4 treats photoelectrochemistry (PEC), an emerging technology. Chapter 1 focuses on the characteristics of deep states in wide band-gap III-V compound semiconductors, particularly the recombination proper- ties which control minority-carrier lifetime and luminescence efficiency. These properties are significant for many optoelectronic devices, includ- ing lasers, LEDs, and solar cells. While this review emphasizes areas of extensive recent development, it also provides references to previous comprehensive reviews. The compilation of levels reported in GaAs and GaP since 1974 is an important contribution, as is the discussion of the methods used to characterize these levels. Recombination at and excitation from deep levels are emphasized. Nonradiative transitions at defect levels-Auger, cascade capture, and multiphonon emission processes-are discussed in detail. Factors to be considered in the analysis of optical cross sections which can give infor- mation about the parity of the impurity wave function and thus about the symmetry of a particular center are reviewed. In Chapter 2, not only are the electrical and optical properties of semi- insulating GaAs discussed, but also the measurement techniques are criti- cally reviewed. GaAs digital IC and monolithic microwave IC technolo- gies are dependent on the development of reliable substrate materials and an understanding of the deep levels of GaAs. Thus these first two chapters provide an important background to the discussion of the crystal growth and device fabrication techniques for GaAs, which are the subjects of Volume 20 of this treatise “Semiconductors and Semimetals .” Automated computer-controlled measurement techniques for Hall ef- fect, photoconductivity, and photo-Hall measurements in semi-insulating ix