Table Of ContentTrap Level Spectroscopy in Amorphous
Semiconductors
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Trap Level Spectroscopy in
Amorphous Semiconductors
Victor I. Mikla and Victor V. Mikla
AMSTERDAM • BOSTON • HEIDELBERG • LONDON • NEW YORK • OXFORD
PARIS • SAN DIEGO • SAN FRANCISCO • SINGAPORE • SYDNEY • TOKYO
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First edition 2010
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ISBN : 978-0-12-384715-7
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Contents
Acknowledgments vii
1 Defect States Spectroscopy in Amorphous Semiconductors 1
1.1 Introduction 1
1.2 General Principles 2
2 Thermally Stimulated Depolarization Currents in
Amorphous Chalcogenides 21
2.1 Background 21
2.2 Theoretical Background 23
2.3 TSDCs in Se-Based Amorphous Semiconductors:
Experimental Results 28
2.4 TSDC in Pure Selenium 29
2.5 TSDC in As(Sb)x Se 1 (cid:2) x Alloys 31
3 Carrier Transport Processes in Amorphous Solids 37
3.1 Background 37
3.2 Experimental Techniques for the Measurement of
Carrier Mobility 39
3.3 Significance of Carrier Transport Data in Various
Applications 42
3 .4 Conventional Dispersion Behavior 43
3.5 Anomalous Dispersive Characteristics 44
4 Time-of-Flight Experiments in Amorphous Chalcogenide
Semiconductors 53
4.1 An Apparatus for IFTOF Measurements 56
4.2 XTOF Technique 61
4.3 TOF Measurements in Selenium-Based Amorphous
Multilayer Photoconductors 6 6
5 Xerographic Spectroscopy of States in Mobility Gap 79
5.1 Schematic Overview of the Xerographic Photocopying Process 80
5.2 Xerography in Animation 83
5.3 Xerographic Dark Decay and Photoinduced Effects 85
vi Contents
6 Photoinduced Effects on States in the Mobility Gap 95
6.1 Introduction 95
6.2 Steady-State Photocurrents 9 5
6.3 Light-Induced Effects on Photocurrent Transients 9 6
7 Spectroscopic Studies of Gap States and Laser-Induced
Structural Transformations in Se-Based As-Free Amorphous
Semiconductors 103
7.1 Preparation of Amorphous Films: Essential Results and
Interpretation 103
7.2 The Basic Properties 105
7.3 Dark Discharge 107
7.4 Transient Photoconductivity 108
7.5 Photoinduced Discharge Characteristics 109
7.6 Optical Properties 114
7.7 Structural Transformation 116
Acknowledgments
I would like to express my sincere thanks to Lisa Tickner (Elsevier), Lisa Jones
(Elsevier), and Mani Prabakaran (MPS Limited) for their patience, continued inter-
est, and helpful comments, which have made it possible for this book to reach
completion.
U ndoubtedly, without the inspiration of my wife, Ottilia, this material could never
have become a book.
Victor I. Mikla
Uzhgorod
March 2010
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1
Defect States Spectroscopy in
Amorphous Semiconductors
Contents
1.1 Introduction 1
1.2 General Principles 2
1.2.1 Basic Types of Relaxation Techniques 2
1.2.2 The Principle of Detailed Balance and Classification of Trapping States 2
1.2.3 Trap Level Spectroscopy: Experimental Methods 5
1.2.4 Direct Methods 6
1.2.5 Indirect Methods 6
1.2.6 TSL and TSC: Retrospective Glance 7
1.2.7 Defect States in Semiconductors and Insulators 9
1.2.8 Field-Induced Thermally Stimulated Currents 10
1.2.9 Remarks on TSC/TSL 12
1.1 Introduction
Amorphous semiconductors are characterized by properties that are absent in their
crystalline counterparts. On the one hand, they are “u nsuitable” objects both for
experimentalists and from the theoretical point of view; on the other hand, they have
widespread technical applications. Therefore, trap level spectroscopy in materials
containing S, Se, and Te is necessary for further technical applications. Currently,
there is no universal technique that probes the full spectrum of trapping levels in
a mobility gap; experimentalists use several complementary methods. This book
is devoted to techniques that probe states in the mobility gap and the results of
their use.
The book is an encyclopedia in the sense that it gives “ starting ” information about
a wide range of spectroscopic techniques in disordered materials. The author only
provides brief, annotated descriptions of these techniques, their advantages, and
experimental results that are typical for the objects considered.
Trap Level Spectroscopy in Amorphous Semiconductors. DOI:10.1016/B978-0-12-384715-7.00001-2
Copyright © 22001100 by Elsevier Inc. All rights of reproduction in any form reserved.
