M. W. Wu

Spin dynamics in semiconductors

This article reviews the current status of spin dynamics in semiconductors which has achieved much progress in the recent years due to the fast growing field of semiconductor spintronics. The primary focus is on the theoretical and experimental developments of spin relaxation and dephasing in both spin precession in the time domain and spin diffusion and transport in the spatial domain. A fully microscopic many-body investigation on spin dynamics based on the kinetic spin Bloch equation approach is comprehensively reviewed.

Theory of the Spin Relaxation of Conduction Electrons in Silicon

A realistic pseudopotential model is introduced to investigate the phonon-induced spin relaxation of conduction electrons in bulk silicon. We find a surprisingly subtle interference of the Elliott and Yafet processes affecting the spin relaxation over a wide temperature range, suppressing the significance of the intravalley spin-flip scattering, previously considered dominant, above roughly 120 K. The calculated spin relaxation times T1 agree with the spin resonance and spin injection data, following a T(-3) temperature dependence. The valley anisotropy of T1 and the spin relaxation rates for hot electrons are predicted.

CURRENT-VOLTAGE CHARACTERISTIC OF ORGANIC LIGHT EMITTING DIODES

It has been claimed that the variation of current I with voltage V in an organic light emitting diode (LED), based on either metal chelate complexes or conducting polymers, is explained by shallow traps that trap carriers propagating in the conduction or valence band. However, because these are disordered materials all states are localized. We show that it is possible to fit the dependence of I on V and on film thickness without explicitly introducing traps, but taking their effect into account by including the mobility variation with the electric field that arises from the distribution in energy of the localized levels.

CONTACT INJECTION INTO POLYMER LIGHT-EMITTING DIODES

The variation of current I with voltage V for poly(phenylene vinylene) and other polymer light-emitting diodes has been attributed to carriers tunneling into broad conduction and valence bands. In actuality the electrons and holes tunnel into polaron levels and transport is by hopping among these levels. We show that for small injection the I–V characteristic is determined mainly by the image force, for large injection by space charge effects, but in both cases the strong variation of mobility with field due to disorder plays an important role.

Spin-orbit coupling in bulk ZnO and GaN

Using group theory and Kane-type k⋅p model together with the Lowdin partition method, we derive the expressions for the spin-orbit coupling of electrons and holes, including the linear-k Rashba term due to the intrinsic structure inversion asymmetry and the cubic-k Dresselhaus term due to the bulk inversion asymmetry in wurtzite semiconductors. The coefficients of the electron and hole Dresselhaus terms of ZnO and GaN in wurtzite structure and GaN in zinc-blende structure are calculated using the nearest-neighbor sp3 and sp3s∗ tight-binding models, respectively.

Kinetics of spin coherence of electrons in an undoped semiconductor quantum well

We study the kinetics of spin coherence of optically excited electrons in an undoped insulating ZnSe/Zn

Kinetic theory of spin transport in n-type semiconductor quantum wells

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Spin-dependent quantum transport in periodic magnetic modulations: Aharonov–Bohm ring structure as a spin filter

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Spin-dependent transport in lateral periodic magnetic modulations: Scheme for spin filters

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Anisotropic spin transport in GaAs quantum wells in the presence of competing Dresselhaus and rashba spin-orbit coupling

Se quantum well under moderate magnetic fields in the Voigt configuration. After clarifying the optical coherence and the spin coherence, we build the kinetic Bloch equations and calculate dephasing and relaxation kinetics of laser pulse excited plasma due to statically screened Coulomb scattering and electron hole spin exchange. We find that the Coulomb scattering can not cause the spin dephasing, and that the electron-hole spin exchange is the main mechanism of the spin decoherence. Moreover the beat frequency in the Faraday rotation angle is determined mainly by the Zeeman splitting, red shifted by the Coulomb scattering and the electron hole spin exchange. Our numerical results are in agreement with experiment findings. A possible scenario for the contribution of electron-hole spin exchange to the spin dephasing of the