Elsevier Radarweg 29, PO Box 211, 1000 AE Amsterdam, The Netherlands Linacre House, Jordan Hill, Oxford OX2 8DP, UK First edition 2010 Copyright # 2010 Elsevier Ltd. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means electronic, mechanical, photocopying, recording or otherwise without the prior written permission of the publisher. Permissions may be sought directly from Elsevier’s Science & Technology Rights Department in Oxford, UK: phone (þ44) (0) 1865 843830; fax (þ44) (0) 1865 853333; email:
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LIST OF CONTRIBUTORS
N. Audet 5N Plus Inc., 4405 rue Garand, Montreal, Canada H4R 2B4. K.W. Benz Freiburger, Materialforschungszentrum, Stefan-Meier-Strasse 21, D-79104 Freiburg, Germany. A.W. Brinkman Science Laboratories, University of Durham, South Road, Durham DH1 3LE, UK. J. L’Ecuyer 5N Plus Inc., 4405 rue Garand, Montreal, Canada H4R 2B4. M. Fiederle Freiburger, Materialforschungszentrum, Stefan-Meier-Strasse 21, D-79104 Freiburg, Germany. G.L. Herrit II-VI Incorporated, 375 Saxonburg Blvd., Saxonburg, PA 16056, USA. R.B. James Brookhaven National Laboratory, Upton, NY 11973, USA. Carl J. Johnson II-VI Incorporated, 375 Saxonburg Blvd., Saxonburg, PA 16056, USA. P.G. Kasherininov A.F. Ioffe Physico-Technical Institute, 26 Polytechnicheskaya Street, St Petersburg 194021, Russia. D. Lincot Laboratoire d’Electrochimie et de Chimie Analytique, UMR 7575, ENSCP-CNRS, 11 rue Pierre et Marie Curie, F-75231 Paris, France. J.-Y. Moisan 4 A Route Crech Argant, F-22730 Tregastel, France. E.R. Mueller Coherent Inc., DEOS, 1280 Blue Hills Avenue, Bloomfield, CT 06002, USA.
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List of Contributors
D. Shink 5N Plus Inc., 4405 rue Garand, Montreal, Canada H4R 2B4. V.N. Tomashik V.Ye. Lashkaryov Institute for Semiconductor Physics of National Academy of Sciences of Ukraine, 41 av. Nauki, Kyiv, Ukraine. Z.F. Tomashik V.Ye. Lashkaryov Institute for Semiconductor Physics of National Academy of Sciences of Ukraine, 41 av. Nauki, Kyiv, Ukraine. A.A. Tomasov A.F. Ioffe Physico-Technical Institute, 26 Polytechnicheskaya Street, St Petersburg 194021, Russia. R. Triboulet CNRS, GEMaC (Groupe d’Etude de la Matie`re Condense´e), 1 Place A. Briand, F-92195 Meudon Cedex, France. Ge Yang Brookhaven National Laboratory, Upton, NY 11973, USA.
FOREWORD
Thirty years after the remarkable monography of K. Zanio and the numerous conferences and papers dedicated since that time to CdTe and CdZnTe, after all the significant progresses in that field and the increasing interest in these materials for their extremely attractive fundamental properties and industrial applications, the editors have thought timely to edit a book on CdTe and CdZnTe, covering all their most prominent, modern, and fundamental aspects. The subject has become so wide and enriched during these 30 years that we have decided to call in well-known specialists and experts of the field. The editors would like to thank them deeply for their valuable contributions, with special acknowledgments to Dr Henri Mariette for his pertinent recommendations and his continued help and support. This part covers the topics Crystal Growth Technology and Surfaces, and Applications. The topics Physics, CdTe-Based Nanostructures and Semimagnetic Semiconductors, and Defects have been covered in Part I. R. Triboulet P. Siffert
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I Crystal Growth and Surfaces
Contents
Ia. Technology: Purification of the Cadmium and Tellurium Elements 1. Introduction 2. Extraction and Initial Refining 2.1. Cadmium 2.2. Tellurium 2.3. Zinc 3. Final Refining 3.1. Cadmium 3.2. Tellurium 3.3. Zinc 3.4. Purification of the CdTe and CdZnTe Compounds 3.5. Oxygen Contamination 4. Concluding Remarks References Ib. CdTe and CdZnTe Growth 1. Introduction 2. Phase Equilibria in the Cd-Te System 3. Crystal Growth Versus Cd-Te Chemical Bond Characteristics 4. Synthesis 4.1. Liquid phase synthesis 4.2. Vapor phase synthesis 4.3. Solid state synthesis 4.4. Solution synthesis 5. Container 6. Crystal Growth 6.1. Melt growth 6.2. Solution growth 6.3. Vapor growth 6.4. Solid state recrystallization 7. Bridgman Growth Modeling and Interface Shape Determination
CDTE and Related Compounds
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2010 Published by Elsevier Ltd.
DOI: 10.1016/B978-0-08-096513-0.00001-7
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Crystal Growth Technology and Surfaces
8. CZT Properties 8.1. CZT properties at macroscopic and microscopic scale 8.2. Segregation 8.3. Solid-vapor equilibrium in the CdTe-ZnTe system 8.4. Industrial growth 9. Purity, Contamination, and Doping 10. Typical Structural and Electronic Properties of CdTe and CZT Crystals 11. Conclusions and Perspectives References Ic. Crystal Growth of CdTe/CdZnTe in Microgravity 1. Introduction: Crystal Growth Under Microgravity 2. Growth from the Vapour Phase 3. Growth by THM with a Rotating Magnetic Field 4. Bridgman Growth Using Dewetting Phenomenon 5. Summary and Outlook References Id. Heteroepitaxial Growth of CdTe Thin Films 1. Introduction 2. Overview of Deposition Methods 2.1. Molecular beam epitaxy 2.2. Hot wall epitaxy 2.3. Close space sublimation 2.4. Atomic layer epitaxy 2.5. Metal organic vapor phase epitaxy 3. Substrate Effects on CdTe Heteroepitaxy 3.1. Growth on Ge 3.2. Growth on Si 3.3. Growth on CdS 3.4. Growth on GaAs 3.5. Growth on NbSe2 4. Outline and Conclusions References Ie. Chemical Treatment of the CdTe and ZnxCd1xTe Surfaces 1. Introduction 2. Bromine and Iodine Containing Etchant Compositions 3. Etchant Compositions Based on Nitric Acid 4. Etchant Compositions Based on Cr(VI) Compounds 5. Etchant Compositions Based on H2O2 6. Halogen-Evolving Etchant Compositions 7. Influence of Doping on Chemical Etching 8. Influence of Crystallographic Orientation on Chemical Etching
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Crystal Growth and Surfaces
9. Chemical Etching of ZnxCd1–xTe Solid Solutions 10. Nanodimensional Formation on CdTe and Zn1–xCdxTe Surfaces at Chemical Etching 11. Conclusion References
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IA Technology: Purification of the Cadmium and Tellurium Elements Jacques L’ Ecuyer, Nicholas Audet and Denis Shink
1. INTRODUCTION Suitable base elements, namely, cadmium, tellurium, and zinc, are required to synthesize and grow high-quality CdTe and CdZnTe crystals. Suitable in this instance implies pure to the extent required to avoid that the final device properties be dominated by extrinsic impurities coming from these base elements. Since the publication of the monograph on CdTe [1] there have been considerable improvements made in the purity of these base elements to the extent where 6Nþ (>99.9999%) base elements are now readily available from commercial vendors. Although denominated as 6Nþ, these are in many cases of even greater purity (9N) if one excludes the carbon, nitrogen, and oxygen content which typically range in the 50–500 part per billion atomic (ppba) level. Significant enough, these substantial improvements in the base element purity have not led to corresponding (expected) improvements in the purity of the CdTe and CdZnTe crystals largely because of remaining contamination issues resulting from the growth process itself [2, 3]. Breakthroughs in analytical techniques are perhaps the most important factor which have been responsible for the improvements in the base element purity over the last 3 decades. More specifically, the routine use of glow discharge mass spectrometry (GDMS) has enabled the direct measurement of purity down to ppba levels [4, 5] for a wide range of impurities in a rapid and reproducible way. This has enabled significant progress to be made in the purification process itself and highlighted the 5N Plus Inc., 4385 Garand Street Montreal, Canada H4R 2B4
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Technology: Purification of the Cadmium and Tellurium Elements
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impact of environmental contamination resulting for example from inappropriate handling and storing practices of these base elements [6]. Commercial vendors and their customers alike are now well aware of such matters and have widely adopted the use of glove boxes, clean rooms, special packaging practices, and materials in an effort to maintain purity at the required levels. Cadmium, tellurium, and zinc, all being relatively low melting metals with high vapor pressures, are amenable to similar purification techniques, especially in the final stages. In most commercial practices these would include a combination of distillation (and/or sublimation) and zone-refining procedures which take advantage of differences in vapor pressure (distillation/sublimation), and changes in solubility between liquid and solid phases. Purity levels of 6Nþ can be obtained using such practices, as shown in Table 1, provided proper attention is given to the quality of the feedstock and appropriate steps are taken to minimize the impact of environmental contamination [7]. In what follows, we review the purification methods used for the base elements, namely, cadmium, tellurium, and zinc, and also examine the approach consisting in the purification of the compounds namely CdTe and/or CdZnTe.
2. EXTRACTION AND INITIAL REFINING Successful and economical purification of the base elements often depends on the suitability of the feedstock that is fed into the final purification stages. For this reason, an integrated purification scheme, involving control over both the initial and final refining stages, is preferred. In this way, it is possible to optimize the entire purification process so that impurities difficult to remove in the final purification stages may be removed earlier on.
2.1. Cadmium Cadmium is a relatively abundant element. World reserves are estimated at 6,000,000 MT [9], and approximately 20,000 MT are produced every year primarily as a by-product of zinc refining; although cadmium is also found in lead and copper ores. Typical cadmium concentrations in zinc concentrates are in the 0.1–0.5% range. Most of the cadmium is eventually recovered following roasting and leaching in sulfuric acid of the zinc concentrate. The resulting zinc sulfate solution, which typically contains up to 100 mg/l of cadmium, is cleaned using a zinc cementation process, whereby fine zinc powder is added to the electrolyte leading to the precipitation of
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Jacques L’ Ecuyer, Nicholas Audet and Denis Shink
Table 1
Typical purity levels of 6Nþ metals as determined by GDMS [8]
ppba
Cd
Te
Zn
ppba
Cd
Te
Zn
Li Be B C N O F Na Mg Al Si P S Cl K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se
