57 Springer Series in Solid-State Sciences Edited by Manuel Cardona Springer Series in Solid-State Sciences Editors: M. Cardona P. Fulde H.-J. Queisser 40 Semiconductor Physics - 50 Multiple Diffraction of X-Rays in Crystals An Introduction By K Seeger By Shih-Lin Chang 41 The LMTO Method 51 Phonon Scattering in Condensed Matter Muffin-Tin Orbitals and Electronic Editors: W. Eisenmenger, K LaBmann, Structure and S. D5ttinger By H. L. Skriver 52 Superconductivity in Magnetic and Exotic 42 Crystal Optics with Spatial Dispersion, Materials and Excitons Editors: T. Matsubara and A Kotani By V. M. Agranovich and V. L. Ginzburg 53 Two-Dimensional Systems, 43 Resonant Nonlinear Interactions of Heterostructures, and Superiattices Light with Matter Editors: G. Bauer, F. Kuchar, By V. S. Butylkin, A E. Kaplan, and H. Heinrich Yu. G. Khronopulo, and E. I. Yakubovich 44 Elastic Media with Microstructure II 54 Magnetic Excitations and Fluctuations Three-Dimensional Models Editors: S. Lovesey, U. Balucani, F. Borsa, ByI.A Kunin and V. Tognetti 45 Electronic Properties of Doped 55 The Theory of Magnetism II. Semiconductors Thermodynamics and Statistical Mechanics By B.!. Shklovskii and A L. Efros By D. C. Mattis 46 Topological Disorder in Condensed Matter 56 Spin Fluctuations in Itinerant Electron Editors: F. Yonezawa and T. Ninomiya Magnetism By T. Moriya 47 Statics and Dynamics of Nonlinear 57 Polycrystalline Semiconductors, Systems Physical Properties and Applications Editors: G. Benedek, H. Bilz, Editor: G. Harbeke and R Zeyher 48 Magnetic Phase Transitions 58 The Recursion Method and Editors: M. Ausloos and R J. Elliott Its Applications Editors: D. Pettifor and D. Weaire 49 Organic Molecular Aggregates, Electronic Excitation and Interaction Processes 59 Dynamical Processes and Editors: P. Reineker, H. Haken, Ordering on Solid Surfaces and H.C. Wolf Editors: A Yoshimori and M. Tsukada Volume 1-39 are listed on the back inside cover Polycrystalline Semiconductors Physical Properties and Applications Proceedings of the International School of Materials Science and Technology at the Ettore Majorana Centre, Erice, Italy, July 1-15, 1984 Editor: G. Harbeke With 159 Figures Springer-Verlag Berlin Heidelberg New York Tokyo 1985 Dr. GUnther Harbeke Laboratories RCA Ltd., Badenerstr. 569 CH-8048 ZUrich, Switzerland Series Editars: Professor Dr. Manuel Cardona Professor Dr. Peter Fulde Professor Dr. Hans-Joachim Queisser Max-Planck-Institut flir Festk6rperforschung, Heisenbergstrasse 1 D-7000 Stuttgart 80, Fed. Rep. of Germany ISBN-13: 978-3-642-82443-2 e-ISBN-13: 978-3-642-82441-8 DOl: 10.1007/978-3-642-82441-8 This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically those of translation, reprinting, reuse of illustrations, broadcasting, reproduction by photocopying machine or similar means, and storage in data banks. Under § 54 of the German Copy right Law, where copies are made for other than private use, a fee is payable to "Verwertungsgesellschaft Wort", Munich. © Springer-Verlag Berlin Heidelberg 1985 Softcover reprint of the hardcover I st edition 1985 The use of registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Bookbinding: J. SchiifferOHG ,6718 Griinstadt. 2153/3130-543210 Preface In terms of structure, the field of semiconductors spans a wide range, from the perfect order of single crystals to the non-periodic, disordered amorph ous state. The two extremes of this range attract a large amount of inter est. On one side, glamorous novel phenomena are being found which can only occur in specially tailored ultra-perfect periodic lattices. On the other side, the exotic and challenging nature of the amorphous state has triggered a surge of activity in recent years. Po1ycrystall i ne semi conductors are in between. They are among the work horses in the field, useful in many applications, a handy solution to many practical problems and still - they have not received in the past the amount of research interest that they deserve. It is the aim of the present book to improve this situation. The book originated from the lectures and seminars presented at the course on "Po1ycrystall i ne Semi conductors - Physical Properties and Applications" of "the International School on Materials Scien ce and Technology, hel d at the Centre for Sci entifi c Culture "Ettore Majorana" in Erice, Italy, July 1-15, 1984. The physics of polycrystalline semiconductors is largely the physics of grain boundaries. Grain boundaries play an essential part in polycrystal1ine semiconductors. The charge carriers perhaps see themselves in the role of the traveller in ancient times who could fairly easily traverse wide areas of flat country or long stretches of a calm sea but had great difficulties in crossing steep mountain ridges and deep river gorges. The present volum? is divided into four parts. In the first part, the fundamental aspects of the physics of grain boundaries are laid out. The use of modern research techniques has greatly increased our knowledge about the detailed atomic structure of grain boundaries and the type of defects which may exist in them. This knowledge forms the basis for total energy calcula tions and facilitates the discussion of atom migration phenomena. In the se cond part, the present state of electronic characterization of grain boundaries is reviewed. The authors deal with the important issues of elec tronic states at and charge transport across grain boundaries. One of the major objectives of these studies is to establish a relationship between the electronic properties of a single boundary in a bi-crystal (ideal situation, easier to study) and those of fil ms with a vi rtually i nfi nite nunber of grain boundaries (real situation, of practical interest). The remaining two parts are mainly devoted to a discussion of the physics involved in using po1ycrystalline semiconductors as parts of active or pas sive electronic and optoelectronic devices. Po1ycrystalline silicon offers the invaluable advantage of a high degree of interfacial compatibility with single crystal silicon and silicon dioxide in microelectronics. Besides its crucial function in integrated-circuit technology it is also a key material v for polycrystalline solar cells. Polycrystalline structures of semiconduc ting compounds such as ZnS and various oxides have found their place in the technology of electroluminescent displays or sensors and varistors, respecti vely . All the chapters on devi ce physi cs stress the necessi ty of a fruitful exchange between fundamental aspects, materials characterization and the technological application. This fruitful exchange became a major achievement of the Erice lecture course, as is reflected in this book. I wish to thank all lecturers and participants for their stimulating con tributions to the success of the course and to the present book. We all have expressed our appreciation for the fine facilities afforded us by the Ettore Majorana Centre and are indebted to its Director, Professor A. Zichichi, to Dr. A. Gabriele, Dr. Pinola Savalli and the staff of the Centre. I am grate ful for the generous support, in particular for student grants, given by the sponsoring institutions European Physical Society, European Research Office, General Electric Co. Wembley, IBM Italia, Italian Ministry of Education, Italian Ministry of Scientific and Technological Research, Italian CNR Group of the Structure of Matter, Laboratories RCA Zurich, Sicilian Regional Go vernment and Siemens AG Munich. Last but not least, I appreciate the advice of the Director of the School, Professor M. Balkanski, and of many friends and colleagues in the field of semiconductors. Zurich, Switzerland Gunther Harbeke December 1984 VI Contents Part I Fundamental Aspects of Grain Boundaries Atomic Structure of Grain Boundaries. By A. Bourret (With 5 Figures) 2 Computer Calculations of Grain Boundary Energies in Germanium and Silicon. By H.J. Moller and H.H. Singer (With 4 Figures) ............. 18 The Geometrical Character of Extended Interfacial Defects in Semiconducting Materials. By R.C. Pond (With 12 Figures) .............. 27 Grain Boundary Segregation. Grain Boundary Diffusion By M. Aucouturier (With 22 Figures) ......................••.......... 47 Part /I Electronic Characterization of Grain Boundaries Electronic Properties of Grain Boundaries By J. Werner (With 15 Figures) ....................................... 76 Electronic States at Grain Boundaries in Semiconductors By A. Broni atowski (With 15 Fi gures) .. .. .. .. .. . .. .. .. .. . .. .. .. .. .. .. . 95 Electrical Properties of Grain Boundaries in the Presence of Deep Bulk Traps. By G. Blatter and F. Greuter (With 7 Figures) ................. 118 Beam Induced Current Characterization in Polycrystalline Semiconductors By C. Donolato (With 17 Figures) ..................................... 138 Part /II Properties and Applications of Polycrystalline Silicon Optical Properties of Polycrystalline Silicon Films By G. Harbeke (With 10 Fi gures) .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .... 156 Polycrystalline Silicon in Integrated Circuits By H.C. de Graaff (With 13 Figures) .................................. 170 VII Part I V Applications of Polycrystalline Semiconductor Compounds Electroluminescence in Polycrystalline Semiconductors By R. Mach (With 21 Figures) ......•.•.••.••.......••...•.••..•..•.••. 186 The Electrical Properties of Oxides Under Conditions of Oxidation, Reduction and Catalysis. By S. Strassler, A. Reis, and D. Wieser 209 Evolution of Physical Models for ZnO-Varistors - A Review By R. Einzinger (With 18 Figures) •..•.•.•.•.•..••.••.••..•.••••••••.. 228 Index of Contributors •••••••..•••••••••••••••..•••••••..••..••••••••. 245 VIII Part I Fundamental Aspects of Grain Boundaries Atomic Structure of Grain Boundaries A. Bourret Departement de Recherche Fondamentale - Physique du Solide, CEN-Grenoble F-85 X-38041 Grenoble Cedex, France ABSTRACT The geometrical description of a general grain boundary in a crys talline structure is first summarized. This includes the definition of the coincidence site lattice (CSL) at particular twin angles and the DSC lattice. Then the dislocation modelling is presented using primary and secondary dislocations. However it is emphasized that this description is not unique. Therefore it is necessary to introduce the structural unit model which describes the core structure of the boundary. A detailed description of these units in cubic diamond structure and their relation to dislocation core structure will be given. A review of the experimental techniques giving some information on atomic structure is made. Few selected examples particularly using the high resolution electron microscopy technique are used to illustra te the different theoretical approaches with emphasis on the structural unit model. It is concluded that our knowledge of the atomic structure of grain boundary in semiconductors is still incomplete. 1. INTRODUCTION Grain boundaries ~.B~ are one of the most common two dimensional extended defects in crystals. Their influence on a large variety of physical proper ties of materials has been largely recognized. Firstly emphasis was given to the influence of GB on mechanical properties at high temperature (G.B. creep or sliding), or on transport properties (enhanced diffusion along G.Bs). In semiconductors their influence on electrical properties is of prime impor tance since the growing interest in employing cheap polycrystalline sili con. It was remarked for a long time, that some G.Bshave practically no effect on electron mobility, although some others have a deleterious effect and affect the efficiency of photovoltaic solar cell : it was clear that such differences should be attributed to the local structure of the G.B. The earliest ideas on the G.B. atomistic structure were given by Rosenhaim and Humphrey [1] who proposed that an amorphous layer is present between the two crystals. Although this old model was discarded for many years it has been proved to be valid in some multicomponent ceramics and sintered powder [2]. However in all other cases and specially in metals or semiconductors it rapidly became evident that GBs were closely related to the crystalline na ture of the material : for instance the orientation dependence of many macroscopic properties is well established. Hargreaves and Hills [8] first proposed models based on a periodic medium at the G.B. interface composed of one atomic plane occupying intermediate positions right between the two crystals (transition lattice theory). Then Mott [9] proposed the island mo del with region of good fit separated by region of poor fit. One of the first observations byetch pit or copper decoration of small angle G.B.in se miconductors [3] gave a firm basis to the idea proposed originally by Burgers [10] that a sub G.B.is composed of a regular array of dislocations. This was formalized by Brandon et al. [11] and developed further by Bollmann [4] 2