N. Samarth

Semiconductor spintronics and quantum computation

1 Ferromagnetic III-V Semiconductors and Their Heterostructures.- 2 Spin Injection and Transport in Micro- and Nanoscale Devices.- 3 Electrical Spin Injection: Spin-Polarized Transport from Magnetic into Non-Magnetic Semiconductors.- 4 Spin Dynamics in Semiconductors.- 5 Optical Manipulation, Transport and Storage of Spin Coherence in Semiconductors.- 6 Spin Condensates in Semiconductor Microcavities.- 7 Spins for Quantum Information Processing.- 8 Electron Spins in Quantum Dots as Qubits for Quantum Information Processing.- 9 Regulated Single Photons and Entangled Photons From a Quantum Dot Microcavity.

Diluted magnetic semiconductors

Diluted magnetic semiconductors (DMSs), i.e. semiconducting crystals whose lattice is made up in part of substitutional magnetic ions (e.g. Cd/sub 1-x/Mn/sub x/Te, Hg/sub 1-x/Fe/sub x/Se, Zn/sub 1-x/Co/sub x/S), are reviewed. The focus is on materials of the type A/sub 1-x//sup II/ Mn/sub x/B/sup VI/, which are the most thoroughly understood. However, the similarities and differences between these materials and the A/sub 1-x//sup II/Fe/sub x/B/sup VI/ and A/sub 1-//sup II/Co/sub x/B/sup VI/ systems are discussed wherever information on the latter system is available. The band structure of the materials, which determines their basic semiconducting properties, is examined. Special attention is given to exchange interactions between the magnetic ions themselves (the d-d interaction) and the interaction between the magnetic ions and band electrons (the sp-d interaction). Magnetic phenomena in DMS alloys are considered. Special attention is given to the physics of layered structures, such as quantum wells and superlattices, involving DMS materials. The prospects of device applications made possible by the properties of DMS alloys are assessed. >

Growth of cubic (zinc blende) CdSe by molecular beam epitaxy

We report the growth of cubic (zinc blende) CdSe epilayers on [100]u2009GaAs substrates by molecular beam epitaxy. The lattice constant of the CdSe epilayers is 6.077 A, and the energy gap is 1.75, 1.74, and 1.67 at 10, 80, and 300 K, respectively.

Molecular beam epitaxy of Zn1−xCdxSe epilayers and ZnSe/Zn1−xCdxSe superlattices

We have investigated the epitaxial growth of Zn1−x CdxSe epilayers and ZnSe/Zn1−x CdxSe superlattices (0≤x≤1) on (100)GaAs. Although thick epilayers of Zn1−x CdxSe are prone to defect formation with increasing Cd content, the structural and optical characteristics improve remarkably when Zn1−x CdxSe isu2009 in theu2009 form ofu2009 thin layersu2009 within ZnSe/Zn1−x CdxSeu2009 superlattices. Highu2009 quality superlatticesu2009 can be grown for x≤0.35. The characterization of these systems using transmission electron microscopy, x‐ray diffraction, reflectivity, and photoluminescence is reported.

Magnetic properties of diluted magnetic semiconductors: A review (invited)

Diluted magnetic semiconductors (DMS) are semiconducting alloys containing a random distribution of substitutional magnetic ions (e.g., Mn++ in Cd1−xMnxSe). Magnetic properties of DMS—such as spin glass behavior due to lattice frustration, magnon excitations in a random system of spins, superexchange, and short range antiferromagnetic order—are of considerable interest in their own right. In addition, understanding these properties is important because they strongly influence the electronic phenomena in DMS via the sp‐d exchange interaction between the band electrons and the localized magnetic moments. We review the most recent results concerning magnetic susceptibility, Mn++‐Mn++ nearest‐neighbor exchange, and magnetic short‐range order in these materials. On this basis, we can present a fairly complete and unified picture of magnetic properties of DMS. In addition, we point out some of the issues and challenges that lie ahead.

Room‐temperature blue lasing action in (Zn,Cd)Se/ZnSe optically pumped multiple quantum well structures on lattice‐matched (Ga,In)As substrates

We report on studies of optically pumped laser action in (Zn,Cd)Se/ZnSe multiple quantum well structures prepared by molecular beam epitaxy on lattice‐matched bulk (Ga,In)As substrates. Room‐temperature lasing under pulsed excitation with threshold pump intensity at I≊500 kW/cm2 has been achieved, together with high repetition ‘‘quasi‐continuous’’ mode operation at temperatures so far up to 100 K.

ROOM-TEMPERATURE EXCITON ABSORPTION IN (ZN,CD)SE/ZNSE QUANTUM WELLS AT BLUE-GREEN WAVELENGTHS

Excitonic absorption has been investigated in multiple quantum wells of (Zn,Cd)Se/ZnSe in an effort to increase the electron‐hole Coulomb interaction. Well‐defined absorption peaks for the n=1 heavy hole exciton are observed at room temperature showing evidence for a reduced exciton‐optical phonon scattering rate.

Spin dynamics and quantum transport in magnetic semiconductor quantum structures

Abstract Quantum structures derived from magnetic semiconductors serve as a powerful arena within which to study the interplay between quantum electronics and thin film magnetism. In particular, the semiconductor aspects of these flexible systems allow direct access to the electronic spin degrees of freedom using both magneto-optical as well as magneto-transport probes. Here we provide an overview of recent developments in the experimental study of II–VI magnetic semiconductor quantum structures, with particular emphasis on the dynamical behavior of field-tunable electronic spin states and spin-dependent quantum transport.

Low threshold pulsed and continuous‐wave laser action in optically pumped (Zn,Cd)Se/ZnSe multiple quantum well lasers in the blue‐green

Laser action in the blue‐green at room temperature has been achieved in pulsed optically pumped (Zn,Cd)Se/ZnSe multiple quantum well structures at threshold intensities Ith≊30 kW/cm2. Continuous‐wave operation in a II‐VI semiconductor laser has also been demonstrated for the first time, here above 100 K. The role of excitons is found to be of importance in defining the lasing mechanism up to room temperature in these quasi‐two‐dimensional wide‐gap heterostructures.

Laser action in the blue-green from optically pumped (Zn,Cd)Se/ZnSe single quantum well structures

We have obtained optically pumped laser action in the form (Zn,Cd)Se/ZnSe single quantum well structures prepared by molecular beam epitaxy. Near‐room‐temperature lasing under pulsed excitation has been achieved and high repetition quasi‐continuous mode operation at temperatures so far up to 120 K. Rapid gain switching has generated pulses of approximate 20 ps in duration.