Photoelectronic Properties Of Semiconductors

The interaction between light and electrons in semiconductors forms the basis for many interesting and practically significant properties. This book examines the fundamental physics underlying this rich complexity of photoelectronic properties of semiconductors, and will familiarise the reader with the relatively simple models that are useful in describing these fundamentals. The basic physics is also illustrated with typical recent examples of experimental data and observations. Following introductory material on the basic concepts, the book moves on to consider a wide range of phenomena, including photoconductivity, recombination effects, photoelectronic methods of defect analysis, photoeffects at grain boundaries, amorphous semiconductors, photovoltaic effects and photoeffects in quantum wells and superlattices. The author is Professor of Materials Science and Electrical Engineering at Stanford University, and has taught this material for many years. He is an experienced author, his earlier books having found wide acceptance and use. Readers will therefore find this volume to be an up-to-date and concise summary of the major concepts, models and results. It is intended as a text for graduate students, but will be an important resource for anyone researching in this interesting field.

This volume discusses the photoelectric behavior of three semiconducting thin film materials hydrogenated amorphous silicon (a Si:H), nano porous titanium dioxide, and the fullerene C60. Despite the fundamental structural differences between these materials, their electronic properties are at least on the phenomenological level surprisingly similar, since all three materials have rather low carrier mobilities. In the last decade a Si:H has conquered large market segments in photo voltaics, fiat panel displays and detector applications. It is surely the most advanced and best understood of the three materials. Nano porous Ti02 is used successfully in a novel solar cell featuring an organic dye absorber. This product is now at the brink of commercialization, while electronic applica tions for C60 still appear to be in the exploration phase. At this stage it appears that some of the insight and many of the exper imental techniques used in the development of a Si:H may prove useful in the on going and yet very basic study of TiO2 and C60 thin films. This idea is the guideline to this book. Without being comprehensive on the part of amorphous silicon, it attempts to outline basic characterization schemes for the nano porous and fullerene materials, and to evaluate their potential for applications with respect to a reference, which is given by a Si:H.

During the past thirty years considerable efforts have been made to design the synthesis and the study of molecular semiconductors. Molecular semiconductors - and more generally molecular materials - involve interactions between individual subunits which can be separately synthesized. Organic and metallo-organic derivatives are the basis of most of the molecular materials. A survey of the literature on molecular semiconductors leaves one rather confused. It does seem to be very difficult to correlate the molecular structure of these semiconductors with their experimental electrical properties. For inorganic materials a simple definition delimits a fairly homogeneous family. If an inorganic material has a conductivity intermediate between that of an 12 1 1 3 1 1 insulator « 10- n- cm- ) and that of a metal (> 10 n- cm- ), then it is a semiconductor and will exhibit the characteristic properties of this family, such as junction formation, photoconductivity, and the photovoltaic effect. For molecular compounds, such simplicity is certainly not the case. A huge number of molecular and macromolecular systems have been described which possess an intermediate conductivity. However, the various attempts which have been made to rationalize their properties have, more often than not, failed. Even very basic electrical properties such as the mechanism of the charge carrier formation or the nature and the density ofthe dopants are not known in detail. The study of molecular semiconductor junctions is very probably the most powerful approach to shed light on these problems.

This volume is devoted exclusively to the interfacial photoelectronic properties of the inorganic layered semiconductors investigated in solid state (Schottky and p-n) photovoltaic and photoelectrochemical (solid/electrolyte) cells. The results of extensive studies on the various interfacial and surface electronic characteristics, interfacial photoreactions and materials aspects of the layered semiconductors reported in the last fifteen years have been reviewed. The layered transition metal dichalcogenides have served as model compounds for the investigation of the details of photoelectrochemical processes and related studies involving surfaces. The layered semiconducting materials have been found to be promising solar cell materials. Significant energy conversion efficiencies have been realized in photoelectrochemical solar cells and in solid state photovoltaic cells. Novel studies including quantum size effects in layered semiconductors have been reported. UHV spectroscopic studies of the surfaces of important layered semiconductors have been given. Recent developments in the preparation of the layered materials have been summarized. New insights into the physical and chemical characteristics of this class of materials have been gained by the studies reported in this book. Highlights include: -- Data on optical and electronic properties of layered semiconductors; -- Solid state and semiconductor/electrolyte junction characteristics; -- Photovoltaic and photoelectrochemical solar cells based on layered materials; -- UHV spectroscopic studies of surfaces of layered semiconductors; -- Quantum size effects in layered semiconductor colloids; -- Novel layered material preparation techniques.

This volume aims at bringing together the results of extensive research done during the last fifteen years on the interfacial photoelectronic properties of the inorganic layered semiconducting materials, mainly in relation to solar energy conversion. Significant contributions have been made both on the fundamental aspects of interface characteristics and on the suitability of the layered materials in photoelectrochemical (semiconductor/electrolyte junctions) and in solid state photovoltaic(Schottky and p-n junctions) cells. New insights into the physical and chemical characteristics of the contact surfaces have been gained and many new applications of these materials have been revealed. In particular, the basal plane surface of the layered materials shows low chemical reactivity and specific electronic behaviour with respect to isotropic solids. In electrochemical systems, the inert nature of these surfaces characterized by saturated chemical bonds has been recognized from studies on charge transfer reactions and catalysis. In addition, studies on the role of the d-band electronic transitions and the dynamics of the photogene rated charge carriers in the relative stability of the photoelectrodes of the transition metal dichalcogenides have deepened the understanding of the interfacial photoreactions. Transition metal layered compounds are also recognized as ideal model compounds for the studies Involving surfaces: photoreactions, adsorption phenomena and catalysis, scanning tunneling microscopy and spectroscopy and epitaxial growth of thin films. Recently, quantum size effects have been investigated in layered semiconductor colloids.

This book provides introductory, comprehensive, and concise descriptions of amorphous chalcogenide semiconductors and related materials. It includes comparative portraits of the chalcogenide and related materials including amorphous hydrogenated Si, oxide and halide glasses, and organic polymers. It also describes effects of non-equilibrium disorder, in comparison with those in crystalline semiconductors.

It is widely recognized that an understanding of the optical pro perties of matter will give a great deal of important information re levant to the fundamental physical properties. This is especially true in semiconductor physics for which, due to the intrinsic low screening of these materials, the optical response is quite rich. Their spectra reflect indeed as well electronic as spin or phonon transitions. This is also in the semiconductor field that artificial structures have been recently developed, showing for the first time specific physical properties related to the low dimentionality of the electronic and vi bronic properties : with this respect the quantum and fractional quan tum Hall effects are among the most well known aspects. The associated reduced screening is also a clear manifestation of these aspects and as such favors new optical properties or at least significantly enhan ces some of them. For all these reasons, it appeared necessary to try to review in a global way what the optical investigation has brought today about the understanding of the physics of semiconductors. This volume collects the papers presented at the NATO Advanced study Inst i tut e on "Optical Properties of Semiconductors" held at the Ettore Majorana Centre, Erice, Sicily on March 9th to 20th, 1992. This school brought together 70 scientists active in research related to optical properties of semiconductors. There were 12 lecturers who pro vided the main contributions .

The purpose of this book is to provide the reader with a self-contained treatment of fundamen tal solid state and semiconductor device physics. The material presented in the text is based upon the lecture notes of a one-year graduate course sequence taught by this author for many years in the ·Department of Electrical Engineering of the University of Florida. It is intended as an introductory textbook for graduate students in electrical engineering. However, many students from other disciplines and backgrounds such as chemical engineering, materials science, and physics have also taken this course sequence, and will be interested in the material presented herein. This book may also serve as a general reference for device engineers in the semiconductor industry. The present volume covers a wide variety of topics on basic solid state physics and physical principles of various semiconductor devices. The main subjects covered include crystal structures, lattice dynamics, semiconductor statistics, energy band theory, excess carrier phenomena and recombination mechanisms, carrier transport and scattering mechanisms, optical properties, photoelectric effects, metal-semiconductor devices, the p--n junction diode, bipolar junction transistor, MOS devices, photonic devices, quantum effect devices, and high speed III-V semiconductor devices. The text presents a unified and balanced treatment of the physics of semiconductor materials and devices. It is intended to provide physicists and mat erials scientists with more device backgrounds, and device engineers with a broader knowledge of fundamental solid state physics.