The study of semiconductor heterostructures started more than forty years ago. In the 1980s this area of research moved to the forefront of semiconduc­ tor physics, largely due to progress in growth technologies which are now capable of producing ultrathin layers (up to a few monolayers) of different semiconductor materials. The availability of structures with nearly ideal, well-controlled properties has made semiconductor heterostructures a test­ ing ground for solid-state physics. These structures have had a profound impact on basic research in semiconductor physics by opening new possibil­ ities for studying low-dimensional electrons, as well as the atomic and elec­ tronic properties of interfaces. Semiconductor heterostructures have also a variety of important practical applications: they provide a material basis for a number of novel devices, and also open the way for improving the operating characteristics of traditional micro- and optoelectronic compo­ nents. As a result of the growing importance of heterostructure physics, more and more people are entering this dynamic field, either from graduate school or from other areas of research. For the new entrants, the task of familiariz­ ing themselves with the vast body of existing knowledge about heterostruc­ tures has become quite a challenge, due to the rapid development of the field and its increasing subdivision into distinct subfields. Even for those who already work in one area of heterostructure physics, keeping up with the developments in neighboring areas is not an easy task. The purpose of this book is to make heterostructure physics more accessible.

Heterostructures, made by growing several ultrathin layers of different materials (down to a few atoms in thickness) on top of a silicon or other substrates, have remarkable properties not shared by bulk materials. One can, for example, confine the motions of electrons to a single layer, making it possible to investigate effectively two- dimensional systems. One can also build materials with large-scale periodicities by alternating layers of different compositions, thereby modulating the optical and electronic properties of the resulting structure. This graduate-level textbook provides the theoretical basis and the relevant experimental knowledge underlying our present understanding of the electrical and optical properties of

1 Electronic Structure of Abrupt Heterojunctions.- 1.1 Band Diagrams of Heterostructures.- 1.2 k · p Model for Heterojunctions.- 1.3 Shallow Electronic States at Heterojunctions.- 1.4 Field-Induced Interface States.- 1.5 Intervalley Mixing at Heterojunctions.- 1.6 Numerical Methods for the Description of Heterostructures 27 Bibliography Notes.- 2 Electrons in Low-Dimensional Structures.- 2.1 Formation of Confined Electronic States.- 2.2 Electronic States in Quantum Wells, Wires, and Dots.- 2.3 Self-Consistent Electronic States in Quantum Wells.- 2.4 More Complex Quantum Wells.- 2.5 Mixing of Hole States in Heterostructures.- 2.6 Multiband k · p Approximation.- 2.7 Electronic States in the Presence of Strain.- Bibliography Notes.- 3 Tunneling in Heterostructures.- 3.1 Tunneling Transmission.- 3.2 Tunnel-Coupled Levels.- 3.3 Superlattices.- 3.4 Superlattices Formed by States of Different Origin.- Bibliography Notes.- 4 Impurity States and Excitons in Heterostructures.- 4.1 Electron Localization on Imperfections.- 4.2 Impurity States in Quantum Wells.- 4.3 Quantum Well Excitons.- 4.4 Excitons in Other Heterostructures.- Bibliography Notes.- 5 Interband Optical Transitions in Heterostructures.- 5.1 Absorption of Light by a 2D Layer.- 5.2 Polarization Dependence of the Interband Transitions.- 5.3 Interband Absorption Spectra in Heterostructures.- 5.4 Excitonic Absorption.- 5.5 Electrooptics of Heterostructures.- 5.6 Modulation Spectroscopy of Heterostructures.- Bibliography Notes.- 6 Radiative Processes in Heterostructures.- 6.1 Theory of Luminescence in 2D Systems.- 6.2 Spectral and Polarization Dependencies of Luminescence.- 6.3 Luminescence from Complex Heterostructures.- 6.4 Radiative Recombination.- Bibliography Notes.- 7 Scattering of Light on Low-DimensionalElectrons.- 7.1 Scattering Cross-Section.- 7.2 Raman Spectroscopy of Intersubband Excitations.- 7.3 Scattering on Collective Electronic Excitations.- Bibliography Notes.- 8 Intersubband Optical Transitions.- 8.1 Resonant Transitions and Excitation into the Continuum.- 8.2 Intersubband Transitions for In-Plane Electric Field.- 8.3 Depolarization Shift and Coulomb Renormalization.- 8.4 Submillimeter Intersubband Transitions.- 8.5 Radiative Intraband Transitions in Heterostructures.- Bibliography Notes.- 9 Nonlinear Optics of Heterostructures.- 9.1 Nonlinear Response.- 9.2 Nonlinear Susceptibilities.- 9.3 Photoelectric Phenomena.- 9.4 Nonlinearities Induced by Electron-Hole Pairs.- Bibliography Notes.- 10 Ultrafast Processes in Heterostructures.- 10.1 Ultrafast Optical Excitation.- 10.2 Carrier Relaxation Processes.- 10.3 Coherent Optics of Heterostructures.- 10.4 Ultrafast Charge Dynamics in Heterostructures.- Bibliography Notes.- 11 Heterostructure-Based Optoelectronic Devices.- 11.1 Heterostructure Lasers.- 11.2 Electrooptic Modulators.- 11.3 Photodetectors.- 11.4 Intersubband Optoelectronic Devices.- 11.5 Optical Characterization of Heterostructures.- Bibliography Notes.- A k · p Method for Bulk Semiconductors.- A.I Nondegenerate Band.- A.2 Two-Band Model.- A.3 Luttinger Model.- A.4 Kane Model.- A.5 Effects of External Fields.- A.6 Effects of Deformation.- Bibliography Notes.- B Electromagnetic Waves in Layered Media.- B.I Modes in a Layered Medium.- B.2 Second Quantization of the Field.- Bibliography Notes.- C Kinetic Equations for Electrons and Photons.- C.I Kinetic Equations Approach.- C.2 Wigner Function for Photons.- C.3 Electron Response.- C.4 Conductivity and Generation Rate.- Bibliography Notes.- D Coulomb Effects in Heterostructures.- D.I Mean FieldTreatment of Coulomb Effects.- D.2 Matrix Elements for 3D, 2D, and ID States.- D.3 Intraband Density Matrix Equations.- D.4 Semiconductor Bloch Equations.- D.5 Beyond the Mean-Field Approximation.- Bibliography Notes.- References.