Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics.

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Spintronics: Fundamentals and applications

The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale and, equally important, that these properties * To whom correspondence should be addressed. Phone, 404-8940292; fax, 404-894-0294; e-mail, mostafa.el-sayed@ chemistry.gatech.edu. † Case Western Reserve UniversitysMillis 2258. ‡ Phone, 216-368-5918; fax, 216-368-3006; e-mail, burda@case.edu. § Georgia Institute of Technology. 1025 Chem. Rev. 2005, 105, 1025−1102

Chemistry and properties of nanocrystals of different shapes.

We present a comprehensive, up-to-date compilation of band parameters for the technologically important III–V zinc blende and wurtzite compound semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other.

Band parameters for III–V compound semiconductors and their alloys

We propose an electron wave analog of the electro‐optic light modulator. The current modulation in the proposed structure arises from spin precession due to the spin‐orbit coupling in narrow‐gap semiconductors, while magnetized contacts are used to preferentially inject and detect specific spin orientations. This structure may exhibit significant current modulation despite multiple modes, elevated temperatures, or a large applied bias.

Electronic analog of the electro‐optic modulator

The invention concerns a quantum cascade laser comprising in particular a gain region (14) consisting of several layers (20) each including: alternating strata of a first type (28) defining each an AllnAs quantum barrier and strata of a second type (28) defining each an InGaAs quantum barrier, and injection barriers (22), interposed between two of the layers (20). The layers of the gain region (14) form each an active zone extending from one to the other of the injection barriers (22) adjacent thereto. The strata (26, 28) are dimensioned such that: each of the wells comprises, in the presence of an electric field, at least a first upper subband, a second median subband, and a third lower subband, and the probability of an electron being present in the first subband is highest in the proximity of one of the adjacent injection barriers, in the second subband in the median part of the zone and in the third subband in the proximity of the other adjacent barriers. The laser is formed by a succession of active zones and injection barriers, without interposition of a relaxation zone.

https://science.sciencemag.org/content/sci/264/5158/553.full.pdf

Quantum cascade laser

Jasprit Singh presents the underlying physics behind devices that drive today's technologies, utilizing carefully chosen solved examples to convey important concepts. Real-world applications are highlighted throughout the book, stressing the links between physical principles and actual devices. The volume provides engineering and physics students and professionals with complete coverage of key modern semiconductor concepts. A solutions manual and set of viewgraphs for use in lectures is available for instructors, from solutions@cambridge.org.

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Electronic and Optoelectronic Properties of Semiconductor Structures

Time-resolved differential transmission measurements of self-assembled ${\mathrm{In}}_{0.4}{\mathrm{Ga}}_{0.6}\mathrm{As}$ quantum dots clearly indicate a phonon bottleneck between the $n\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}2$ and $n\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$ electronic levels. The key to this observation is the generation of electrons in dots where there are no holes so that electron-hole scattering does not mask the bottleneck. We use a simple carrier capture model consisting of two capture configurations to explain the bottleneck signal and offer arguments to rule out other possible sources of the signal.

Observation of Phonon Bottleneck in Quantum Dot Electronic Relaxation

Strained epitaxy has been shown to produce pyramidal-shaped quantum dot structures by single-step epitaxy. In this paper we examine the strain tensor in these quantum dots using a valence force field model. We use an eight-band $\mathbf{k}\ensuremath{\cdot}\mathbf{p}$ formalism to find the electronic spectra in the highly strained dots. Results obtained for the conduction-band spectra using the effective-mass approach are shown to have serious errors. This is particularly true for excited states in the conduction band. The dependence of the electronic spectra on the quantum dot size and shape is also reported along with comparisons with published experimental results.

Strain distribution and electronic spectra of InAs/GaAs self-assembled dots: An eight-band study

Theoretical and experimental studies are presented to understand the initial stages of growth of InGaAs on GaAs. Thermodynamic considerations show that, as strain increases, the free‐energy minimum surface of the epilayer is not atomically flat, but three‐dimensional in form. Since by altering growth conditions the strained epilayer can be grown near equilibrium or far from equilibrium, the effect of strain on growth modes can be studied. In situ reflection high‐energy electron diffraction studies are carried out to study the growth modes and surface lattice spacing before the onset of dislocations. The surface lattice constant does not change abruptly from that of the substrate to that of the epilayer at the critical thickness, but changes monotonically. These observations are consistent with the simple thermodynamic considerations presented.

https://deepblue.lib.umich.edu/bitstream/handle/2027.42/70448/APPLAB-53-8-684-1.pdf?sequence=2

Role of strain and growth conditions on the growth front profile of InxGa1−xAs on GaAs during the pseudomorphic growth regime

Carrier relaxation in self-organized ${\mathrm{In}}_{0.4}{\mathrm{Ga}}_{0.6}\mathrm{A}\mathrm{s}/\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}$ quantum dots is investigated by time-resolved differential transmission measurements. The dots have a base dimension of around 14 nm and a height of 7 nm, leading to an average energy separation of the ground and first excited electronic states much greater than the LO-phonon energy, so the phonon-mediated electron relaxation is expected to be slow. Our measurements indicate that, even at low carrier densities (less than one electron-hole pair per dot), the electron and hole relaxation time constants are 5.2 and 0.6 ps, respectively; this indicates a lack of any ``phonon bottleneck'' and is consistent with a model of electrons scattering from holes which can relax rapidly via phonon emission.

Jasprit Singh

Papers

Electronic and Optoelectronic Properties of Semiconductor Structures

Observation of Phonon Bottleneck in Quantum Dot Electronic Relaxation

Strain distribution and electronic spectra of InAs/GaAs self-assembled dots: An eight-band study

Role of strain and growth conditions on the growth front profile of InxGa1−xAs on GaAs during the pseudomorphic growth regime

Rapid carrier relaxation in In 0.4 Ga 0.6 A s / G a A s quantum dots characterized by differential transmission spectroscopy