Shah Hot Carriers in Semiconductor Nanostructures

Physics and Applications
1. Auflage 2012
ISBN: 978-0-08-092570-7
Verlag: Elsevier Science & Techn.
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 508 Seiten

Nonequilibrium hot charge carriers play a crucial role in the physics and technology of semiconductor nanostructure devices. This book, one of the first on the topic, discusses fundamental aspects of hot carriers in quasi-two-dimensional systems and the impact of these carriers on semiconductor devices. The work will provide scientists and device engineers with an authoritative review of the most exciting recent developments in this rapidly moving field. It should be read by all those who wish to learn the fundamentals of contemporary ultra-small, ultra-fast semiconductor devices. - Topics covered include - Reduced dimensionality and quantum wells - Carrier-phonon interactions and hot phonons - Femtosecond optical studies of hot carrier - Ballistic transport - Submicron and resonant tunneling devices

Autoren/Hrsg.

Shah, Jagdeep

Inhaltsverzeichnis

1;Front Cover;1
2;Hot Carriers In Semiconductor Nanostructures: Physics and Applications;4
3;Copyright Page;5
4;Table of Contents;8
5;Preface ;14
6;Contributors;16
7;Part I: Overview;18
7.1;Chapter I.1. Overview;20
7.1.1;1. Introduction;20
7.1.2;2. Fundamental Aspects of Quasi-2D Systems ;22
7.1.3;3. Monte Carlo Simulations;26
7.1.4;4. Optical Studies of Hot Carriers in Semiconductor Nanostructures;27
7.1.5;5. Transport Studies and Devices;29
7.1.6;6. Summary;30
7.1.7;References;31
8;Part II: Fundamental Theory;32
8.1;Chapter II.l. Electron–Phonon Interactions in 2D Systems;34
8.1.1;1. Introduction;34
8.1.2;2. Quantum Confinement.;37
8.1.3;3. The Electron–Phonon Scattering Rate.;47
8.1.4;4. Model Rates for the Fröhlich Interaction;51
8.1.5;5. Scattering by Acoustic Phonons;63
8.1.6;6. Concluding Remarks;66
8.1.7;References;67
8.2;Chapter II.2. Quantum Many-Body Aspects of Hot-Carrier Relaxation in Semiconductor Microstructures;70
8.2.1;1. Introduction;70
8.2.2;2. Energy Relaxation of an Excited Electron Gas;77
8.2.3;3. Single-Particle Inelastic Lifetime;93
8.2.4;4. Conclusion;99
8.2.5;Acknowledgments;100
8.2.6;References;100
8.3;Chapter II.3. Cooling of Highly Photoexcited Electron–Hole Plasma in Polar Semiconductors and Semiconductor Quantum Wells:A Balance-Equation Approach;104
8.3.1;1. Carrier Cooling in Bulk Polar Semiconductors;104
8.3.2;2. Carrier Cooling in Quantum-Well Structures;117
8.3.3;3. Summary and Conclusions;133
8.3.4;References;134
8.4;Chapter II.4. Tunneling Times in Semiconductor Heterostructures: A Critical Review;138
8.4.1;1. Introduction;138
8.4.2;2. Phase Time, Dwell Time, Büttiker-Landauer Time, Larmor Times, and Complex Times;141
8.4.3;3. Analysis and Domain of Validity of the Proposed Tunneling Times;152
8.4.4;4. Experimental Methods for Determining Tunneling Times;163
8.4.5;Acknowledgments;166
8.4.6;References;166
8.5;Chapter II.5. Quantum Transport;170
8.5.1;1. Introduction;170
8.5.2;2. The General Problem and the Various Approaches;173
8.5.3;3. Applications;187
8.5.4;4. Conclusions;203
8.5.5;References;204
9;Part III: Monte Carlo Simulations;206
9.1;Chapter III.l. Hot-Carrier Relaxation in Quasi-2D Systems;208
9.1.1;1. Introduction;208
9.1.2;2. Scattering in Quasi-2D Systems;210
9.1.3;3. Monte Carlo Simulation;221
9.1.4;4. Analysis of Experimental Results;227
9.1.5;5. Summary and Conclusions;248
9.1.6;Acknowledgments;248
9.1.7;References;249
9.2;Chapter III.2. Monte Carlo Simulation of GaAs–AlxGa1_xAs Field-Effect Transistors;252
9.2.1;1. Introduction;252
9.2.2;2. Ensemble Monte Carlo Device Model;254
9.2.3;3. Nonstationary Transport and Scaling of modfets ;260
9.2.4;4. Physics of Real-Space Transfer Transistors;270
9.2.5;5. Extended Drift-Diffusion Formalism;283
9.2.6;6. Conclusions;289
9.2.7;Acknowledgments;289
9.2.8;References;289
10;Part IV: Optical Studies;294
10.1;Chapter IV.l. Ultrafast Luminescence Studies of Carrier Relaxation and Tunneling in Semiconductor Nanostructures;296
10.1.1;1. Introduction;296
10.1.2;2. Ultrafast Luminescence Studies of Carrier Relaxation;300
10.1.3;3. Ultrafast Luminescence Studies of Tunneling in Semiconductor Nanostructures;312
10.1.4;4. Summary;323
10.1.5;Acknowledgments;324
10.1.6;References;324
10.2;Chapter IV.2. Optical Studies of Femtosecond Carrier Thermalization in GaAs;330
10.2.1;1. Introduction;330
10.2.2;2. Experimental Methods;336
10.2.3;3. Experimental Results;337
10.2.4;4. Theoretical Approaches;351
10.2.5;5. Conclusion;358
10.2.6;Acknowledgments;359
10.2.7;References;360
10.3;Chapter IV.3. Time-Resolved Raman Measurements of Electron–Phonon Interactions in Quantum Wells and Superlattices;362
10.3.1;1. Introduction;362
10.3.2;2. Experimental Considerations;364
10.3.3;3. Raman Measurements of Intersubband Relaxation in Quantum Wells;367
10.3.4;4. LO-Phonon Emission in Intrasubband Relaxation;378
10.3.5;5. Phonon-Assisted Charge Transfer in Type II GaAs-AlAs Superlattices;388
10.3.6;6. Summary;393
10.3.7;Acknowledgments;394
10.3.8;References;394
10.4;Chapter IV.4. Electron-Hole Scattering in Quantum Wells;396
10.4.1;1. Introduction;396
10.4.2;2. Experimental Techniques;402
10.4.3;3. Quantitative Results on Momentum and Energy Relaxation;412
10.4.4;4. Photoconductivity Experiments;417
10.4.5;5. Outlook;421
10.4.6;Acknowledgments;422
10.4.7;References;422
11;Part V: Transport Studies;426
11.1;Chapter V.l. Ballistic Transport in a Two-Dimensional Electron Gas;428
11.1.1;1. Hot-Electron Transport;428
11.1.2;2. Hot Ballistic Transport;431
11.1.3;3. Energy Dependence of Hot-Electron Transport;435
11.1.4;4. Ballistic Transport in Upper Subbands;440
11.1.5;5. Angular Distribution and Electron-Beam Steering;447
11.1.6;6. Electrostatic Focusing of Ballistic Electrons;449
11.1.7;7. A Ballistic Hot-Electron Device;453
11.1.8;8. Summary;456
11.1.9;Acknowledgments;457
11.1.10;References;457
11.2;Chapter V.2. Resonant-Tunneling Hot-Electron Transistors;460
11.2.1;1. Introduction;460
11.2.2;2. Modeling of RHET Operation;461
11.2.3;3. Experimental Analyses of RHET Microwave Performance;471
11.2.4;4. RHET Performance Improved by a New Collector Structure;474
11.2.5;5. RHET Logic Family;476
11.2.6;6. Summary;483
11.2.7;Acknowledgments;484
11.2.8;References;484
11.3;Chapter V.3. Resonant Tunneling in High-Speed Double Barrier Diodes;486
11.3.1;1. Introduction;486
11.3.2;2. Principles of Resonant Tunneling;489
11.3.3;3. Resonant-Tunneling Device Physics;496
11.3.4;4. Experimental Results;502
11.3.5;5. Summary;512
11.3.6;Acknowledgments;513
11.3.7;References;513
12;Index;516

Leseproben

I.1

Overview

Jagdeep Shah    AT&T Bell Laboratories Holmdel, New Jersey

1. Introduction   3

2. Fundamental Aspects of Quasi-2D Systems   5

2.1. Electron-Phonon Interaction in Quasi-2D Systems   6

2.2. Many-Body Effects   7

2.3. Hot-Phonon Effects   7

2.4. Scattering Processes Specific to Quasi-2D Systems   8

2.5. Tunneling Times   8

2.6. Quantum Transport   8

3. Monte Carlo Simulations   9

3.1. Monte Carlo Simulations of Ultrafast Optical Studies   9

3.2. Monte Carlo Simulations of Submicron Devices   10

4. Optical Studies of Hot Carriers in Semiconductor Nanostructures   10

4.1. Ultrafast Luminescence Studies of Carrier Relaxation and Tunneling   10

4.2. Femtosecond Pump-and-Probe Transmission Studies   11

4.3. Ultrafast Pump-and-Probe Raman Scattering Studies   11

4.4. Electron–Hole Scattering   12

5. Transport Studies and Devices   12

5.1. Ballistic Transport in Nanostructures   12

5.2. Resonant Tunneling Hot-electron Transistors   13

5.3. Resonant Tunneling Diodes   13

6. Summary   13

References   14

1 INTRODUCTION

In thermal equilibrium, all elementary excitations in a semiconductor (e.g., electrons, holes, phonons) can be characterized by a temperature that is the same as the lattice temperature. Under the influence of an external perturbation such as an electric field or optical excitation, the distribution functions of these elementary excitations deviate from those in thermal equilibrium. In general, the nonequilibrium distribution functions are nonthermal (i.e. cannot be characterized by a temperature). But, under special conditions, they can be characterized by a temperature that may be different for each elementary excitation and different from the lattice temperature. The term “hot carriers” is often used to describe both these nonequilibrium situations.

Investigation of hot-carrier effects plays a central role in modern semiconductor science. Properties of hot carriers are determined by various interactions between carriers and other elementary excitations in the semiconductor. Therefore, investigations of hot-carrier properties provide information about scattering processes that are of fundamental interest in the physics of semiconductors. Furthermore, these processes determine high-field transport phenomena in semiconductors and thus form the basis of many ultrafast electronic and optoelectronic devices. The field of hot carriers in semiconductors thus provides a link between fundamental semiconductor physics and high-speed devices.

Although some theoretical work on high-field transport in semiconductors dates from 1930s, experimental investigations started in 1951 with the high-field experiments of Ryder and Shockley (the early work is referenced by Conwell [1]). These and other investigations that followed in the next quarter of a century concentrated on bulk semiconductors and semiconductor devices, and provided quantitative understanding of many phenomena and new insights into the high-field transport processes in semiconductors. This work is extensively covered in excellent books by Conwell [1], Nag [2,3], and Reggiani [4]. The topic has also been the subject of NATO Advanced Study Institutes [5,6].

The direction of the field changed considerably in 1970s and 1980s because of several developments. The quasi-two-dimensional nature of carriers in the conducting channels in Si mosfets brought into play new physical phenomena [7]. The mid 1970s brought the first high-quality quantum-well heterostructures, consisting of thin layers of semiconductors with different bandgaps and grown using the techniques of molecular-beam epitaxy (for a recent review, see, for example, Madhukar in [8]). Semiconductor nanostructures have led to many exciting developments in the physics of semiconductors [8–10]. Furthermore, the ability to grow and fabricate semiconductor structures on nanometer scales has led to the development of many new devices, such as modulation-doped field-effect transistors and resonant tunneling diodes. Nonequilibrium transport of carriers is a common thread in these ultrasmall, ultrafast devices operating at high electric fields. Ballistic transport in nanonstructures provided another focal point of interest. These developments have led to considerable interest in the investigation of hot-carrier effects in semiconductor nanostructures.

An important milestone in the field of hot carriers in semiconductors was the demonstration in late 1960s that optical excitation can create hot carriers and optical spectroscopy can provide information about the distribution function of hot carriers. Although transport measurements provide considerable information about various scattering processes in semiconductors, they are averaged over the carrier distribution functions. In contrast, optical techniques, by providing the best means of determining the carrier distribution functions, allow one to investigate the microscopic scattering processes. Another development that has significantly altered the course of this field is the recent availability of ultrafast lasers with pulsewidths as short as 6 fs (for a recent review of the field of ultrafast lasers and their applications to physics, chemistry and biology, see [11]). These lasers allowed the investigation of the time evolution of the carrier distribution functions on ultrashort time scales. Since different scattering processes occur on different time scales, it became possible to isolate various scattering processes by appropriate choices of time windows.

The availability of high-speed computers has made it possible to carry out ensemble Monte Carlo simulations of submicron devices and ultrafast carrier relaxation in semiconductors. Detailed comparison of these simulations with the device performance or with experimental observations of carrier relaxations obtained with ultrafast lasers has provided valuable new information.

Finally, the ability to grow nanostructures has led to interesting new transport phenomena such as ballistic transport of electrons and led to devices based on nonequilibrium transport through such nanostructures. Examples of the devices are resonant tunneling diodes, resonant tunneling hot-electron transistors and modulation-doped field-effect transistors.

As one can see from this brief historical survey, the field of hot carriers in semiconductors and their nanostructures has been a dynamic field with many important developments in the past decade. The purpose of this book is to review the most exciting of these developments in the four areas discussed above. The book is divided into four parts, with several chapters in each part. Part II deals with the fundamental aspects of hot-carrier physics in quasi-2D systems. Part III deals with Monte Carlo simulations of ultrafast optical experiments in quasi-2D systems and of submicron devices. Part IV discusses optical studies of hot carriers in quasi-2D systems, and Part V deals with ballistic transport, resonant tunneling transistors and diodes. In the remainder of this chapter, I will present an overview of these developments.

2 FUNDAMENTAL ASPECTS OF QUASI-2D SYSTEMS

Hot-carrier effects are determined by many different scattering processes, such as carrier–carrier scattering, carrier–phonon scattering, intervalley scattering, and intersubband scattering. An understanding of these processes is essential for an understanding of hot-carrier phenomena and devices. These fundamental processes are reviewed in Part II.

2.1 Electron–Phonon Interaction in Quasi-2D Systems

Electronic states in a quantum confined system are different from those in a bulk semiconductor. The conduction and valence bands break up into various subbands as a result of confinement. The wavefunctions of the confined states penetrate into the barrier for finite barrier heights but vanish at the boundary for infinitely high barriers. For thick barriers, each well in a multiple quantum-well structure can be treated as independent of the other wells. With decreasing barrier thickness, the wavefunctions in the adjacent wells overlap with each other and lead to the phenomenon of minibands, with some interesting transport consequences [12]. These modifications of the electronic...