Hot Carriers in Semiconductor Nanostructures (eBook)

Physics and Applications

Jagdeep Shah (Autor)

eBook Download: PDF | EPUB

2012 | 1. Auflage
508 Seiten
Elsevier Science (Verlag)
978-0-08-092570-7 (ISBN)

Infos

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

Inhalt

Front Cover 1
Hot Carriers In Semiconductor Nanostructures: Physics and Applications 4
Copyright Page 5
Table of Contents 8
Preface 14
Contributors 16
Part I: Overview 18
Chapter I.1. Overview 20
1. Introduction 20
2. Fundamental Aspects of Quasi-2D Systems 22
3. Monte Carlo Simulations 26
4. Optical Studies of Hot Carriers in Semiconductor Nanostructures 27
5. Transport Studies and Devices 29
6. Summary 30
References 31
Part II: Fundamental Theory 32
Chapter II.l. Electron–Phonon Interactions in 2D Systems 34
1. Introduction 34
2. Quantum Confinement. 37
3. The Electron–Phonon Scattering Rate. 47
4. Model Rates for the Fröhlich Interaction 51
5. Scattering by Acoustic Phonons 63
6. Concluding Remarks 66
References 67
Chapter II.2. Quantum Many-Body Aspects of Hot-Carrier Relaxation in Semiconductor Microstructures 70
1. Introduction 70
2. Energy Relaxation of an Excited Electron Gas 77
3. Single-Particle Inelastic Lifetime 93
4. Conclusion 99
Acknowledgments 100
References 100
Chapter II.3. Cooling of Highly Photoexcited Electron–Hole Plasma in Polar Semiconductors and Semiconductor Quantum Wells:A Balance-Equation Approach 104
1. Carrier Cooling in Bulk Polar Semiconductors 104
2. Carrier Cooling in Quantum-Well Structures 117
3. Summary and Conclusions 133
References 134
Chapter II.4. Tunneling Times in Semiconductor Heterostructures: A Critical Review 138
1. Introduction 138
2. Phase Time, Dwell Time, Büttiker-Landauer Time, Larmor Times, and Complex Times 141
3. Analysis and Domain of Validity of the Proposed Tunneling Times 152
4. Experimental Methods for Determining Tunneling Times 163
Acknowledgments 166
References 166
Chapter II.5. Quantum Transport 170
1. Introduction 170
2. The General Problem and the Various Approaches 173
3. Applications 187
4. Conclusions 203
References 204
Part III: Monte Carlo Simulations 206
Chapter III.l. Hot-Carrier Relaxation in Quasi-2D Systems 208
1. Introduction 208
2. Scattering in Quasi-2D Systems 210
3. Monte Carlo Simulation 221
4. Analysis of Experimental Results 227
5. Summary and Conclusions 248
Acknowledgments 248
References 249
Chapter III.2. Monte Carlo Simulation of GaAs–AlxGa1_xAs Field-Effect Transistors 252
1. Introduction 252
2. Ensemble Monte Carlo Device Model 254
3. Nonstationary Transport and Scaling of modfets 260
4. Physics of Real-Space Transfer Transistors 270
5. Extended Drift-Diffusion Formalism 283
6. Conclusions 289
Acknowledgments 289
References 289
Part IV: Optical Studies 294
Chapter IV.l. Ultrafast Luminescence Studies of Carrier Relaxation and Tunneling in Semiconductor Nanostructures 296
1. Introduction 296
2. Ultrafast Luminescence Studies of Carrier Relaxation 300
3. Ultrafast Luminescence Studies of Tunneling in Semiconductor Nanostructures 312
4. Summary 323
Acknowledgments 324
References 324
Chapter IV.2. Optical Studies of Femtosecond Carrier Thermalization in GaAs 330
1. Introduction 330
2. Experimental Methods 336
3. Experimental Results 337
4. Theoretical Approaches 351
5. Conclusion 358
Acknowledgments 359
References 360
Chapter IV.3. Time-Resolved Raman Measurements of Electron–Phonon Interactions in Quantum Wells and Superlattices 362
1. Introduction 362
2. Experimental Considerations 364
3. Raman Measurements of Intersubband Relaxation in Quantum Wells 367
4. LO-Phonon Emission in Intrasubband Relaxation 378
5. Phonon-Assisted Charge Transfer in Type II GaAs-AlAs Superlattices 388
6. Summary 393
Acknowledgments 394
References 394
Chapter IV.4. Electron-Hole Scattering in Quantum Wells 396
1. Introduction 396
2. Experimental Techniques 402
3. Quantitative Results on Momentum and Energy Relaxation 412
4. Photoconductivity Experiments 417
5. Outlook 421
Acknowledgments 422
References 422
Part V: Transport Studies 426
Chapter V.l. Ballistic Transport in a Two-Dimensional Electron Gas 428
1. Hot-Electron Transport 428
2. Hot Ballistic Transport 431
3. Energy Dependence of Hot-Electron Transport 435
4. Ballistic Transport in Upper Subbands 440
5. Angular Distribution and Electron-Beam Steering 447
6. Electrostatic Focusing of Ballistic Electrons 449
7. A Ballistic Hot-Electron Device 453
8. Summary 456
Acknowledgments 457
References 457
Chapter V.2. Resonant-Tunneling Hot-Electron Transistors 460
1. Introduction 460
2. Modeling of RHET Operation 461
3. Experimental Analyses of RHET Microwave Performance 471
4. RHET Performance Improved by a New Collector Structure 474
5. RHET Logic Family 476
6. Summary 483
Acknowledgments 484
References 484
Chapter V.3. Resonant Tunneling in High-Speed Double Barrier Diodes 486
1. Introduction 486
2. Principles of Resonant Tunneling 489
3. Resonant-Tunneling Device Physics 496
4. Experimental Results 502
5. Summary 512
Acknowledgments 513
References 513
Index 516

Textauszug

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...

Produkt-Details

• Erscheint lt. Verlag: 2.12.2012
• Sprache: englisch
• Themenwelt: Naturwissenschaften ► Physik / Astronomie ► Festkörperphysik
• Themenwelt: Naturwissenschaften ► Physik / Astronomie ► Quantenphysik
• Themenwelt: Technik ► Elektrotechnik / Energietechnik
• Themenwelt: Technik ► Maschinenbau
• ISBN-10: 0-08-092570-7 / 0080925707
• ISBN-13: 978-0-08-092570-7 / 9780080925707