Co-planar spin-polarized light emitting diode

Studies of spin manipulation in semiconductors has benefited from the possibility to grow these materials in high quality on top of optically active III-V systems. The induced electroluminescence in these layered semiconductor heterostructures has been used for a reliable spin detection. In semiconductors with strong spin-orbit interaction, the sensitivity of vertical devices may be insufficient, however, because of the sepration of the spin aligner part and the spin detection region by one or more heterointerfaces and becuse of the short spin coherence length. Here we demostrate that higly sensitive spin detection can be achieved using a lateral arrangement of the spin polarized and optically active regions. Using our co-planar spin-polarized light emitting diodes we detect electrical field induced spin generation in a semiconductor heterojunction two-dimensional hole gas. The polarization results from spin asymmetric recombination of injected electrons with strongly SO coupled two-dimensional holes. The possibility to detect magnetized Co particles deposited on the co-planar diode structure is also demonstrated.Comment: 8 pages, 3 figure

Modeling of diffusion of injected electron spins in spin-orbit coupled microchannels

We report on a theoretical study of spin dynamics of an ensemble of spin-polarized electrons injected in a diffusive microchannel with linear Rashba and Dresselhaus spin-orbit coupling. We explore the dependence of the spin-precession and spin-diffusion lengths on the strengths of spin-orbit interaction and external magnetic fields, microchannel width, and orientation. Our results are based on numerical Monte Carlo simulations and on approximate analytical formulas, both treating the spin dynamics quantum-mechanically. We conclude that spin-diffusion lengths comparable or larger than the precession-length occur i) in the vicinity of the persistent spin helix regime for arbitrary channel width, and ii) in channels of similar or smaller width than the precession length, independent of the ratio of Rashba and Dresselhaus fields. For similar strengths of the Rashba and Dresselhaus fields, the steady-state spin-density oscillates or remains constant along the channel for channels parallel to the in-plane diagonal crystal directions. An oscillatory spin-polarization pattern tilted by 45$^{\circ}$ with respect to the channel axis is predicted for channels along the main cubic crystal directions. For typical experimental system parameters, magnetic fields of the order of Tesla are required to affect the spin-diffusion and spin-precession lengths.Comment: Replaced with final version (some explanations and figures improved). 8 pages, 6 figure

Low-dimensional light-emitting transistor with tunable recombination zone

We present experimental and numerical studies of a light-emitting transistor comprising two quasi-lateral junctions between a two-dimensional electron and hole gas. These lithographically defined junctions are fabricated by etching of a modulation doped GaAs/AlGaAs heterostructure. In this device electrons and holes can be directed to the same area by drain and gate voltages, defining a recombination zone tunable in size and position. It could therefore provide an architecture for probing low-dimensional devices by analysing the emitted light of the recombination zone.Comment: 12 Pages, to be published in Journal of Modern Optic

Experimental observation of the spin-Hall effect in a two dimensional spin-orbit coupled semiconductor system

We report the experimental observation of the spin-Hall effect in a two-dimensional (2D) hole system with Rashba spin-orbit coupling. The 2D hole layer is a part of a p-n junction light-emitting diode with a specially designed co-planar geometry which allows an angle-resolved polarization detection at opposite edges of the 2D hole system. In equilibrium the angular momenta of the Rashba split heavy hole states lie in the plane of the 2D layer. When an electric field is applied across the hole channel a non zero out-of-plane component of the angular momentum is detected whose sign depends on the sign of the electric field and is opposite for the two edges. Microscopic quantum transport calculations show only a weak effect of disorder suggesting that the clean limit spin-Hall conductance description (intrinsic spin-Hall effect) might apply to our system.Comment: 4 pages, 3 figures, paper based on work presented at the Gordon Research Conference on Magnetic Nano-structures (August 2004) and Oxford Kobe Seminar on Spintronics (September 2004); accepted for publication in Physical Review Letters December 200