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EPSRC Reference: EP/C003659/1
Title: Demonstration of a high-temperature spin-LED based on (110)-oriented quantum wells.
Principal Investigator: Marrows, Professor CH
Other Investigators:
Researcher Co-Investigators:
Dr AT Hindmarch
Project Partners:
Department: Physics and Astronomy
Organisation: University of Leeds
Scheme: Standard Research (Pre-FEC)
Starts: 02 November 2004 Ends: 01 November 2006 Value (£): 20,653
EPSRC Research Topic Classifications:
Materials Characterisation Materials Synthesis & Growth
EPSRC Industrial Sector Classifications:
Electronics
Related Grants:
EP/C511417/1 EP/C003500/1
Panel History:  
Summary on Grant Application Form
The proposal is to fabricate and test a novel form of spin-LED capable of efficient generation of circularly polarised light at room temperature.Intense worldwide interest is being focused on new semiconductor spintronic and spin-optronic quantum devices in which electronic spin replaces charge for data processing or is used to manipulate optical polarisation. Requirements for such devices are injection of a non-equilibrium population of electron spins into the semiconductor from a spin-polarising metal contact and preservation of the spin population for as long as possible following injection. The spin-LED is the best test-bed for these functions as well as having an immediate potential application as a single-polarised-photon source for quantum cryptography. It is a pn junction light emitting diode in which the cathode injects spin-polarised electrons giving circularly polarised light output due to the selection rules for electron-hole recombination; bulk semiconductor allows a theoretical maximum degree of polarisation of 50% whereas a quantum well allows 100%.The novel feature of our proposed design is the use of quantum wells grown on a (110)-oriented substrate rather than (100)-orientation, as used in all spin-LEDs hitherto. At room temperature, although spin-polarised electrons can be efficiently injected into the semiconductor, output polarisation is limited to ~5% or less due to rapid spin-relaxation in the semiconductor before radiative recombination can occur. We have recently shown that the spin-memory of electrons in (110)-oriented GaAs quantum wells is enhanced by ~x100 compared to similar (100) wells at room temperature, confirming theoretical predictions. From this it can be expected that the output polarisation of a (110) spin-LED at room temperature should be high - approaching the limit set by the spin injection process.The operation of the device requires injection of current with the electron spins polarised perpendicular to the quantum well planes. For this we propose several ferromagnetic metal contact designs, based on magnetic tunnel contacts (MTC) and magnetic tunnel transistors (MTT), deposited on top of the quantum wells. For initial tests the ferromagnetic moment of the contact will be aligned by applied magnetic field but we shall also test designs of the metal contact in the form of a ferromagnetic superlattice which will give perpendicular spin-polarisation without applied magnetic field.It is essential for successful realisation of such a device to have collaborators who are collectively expert in the magnetic multilayers for spin-injection, the semiconductor growth and the semiconductor spin-dynamics. Our groups in Leeds, Nottingham and Southampton combine expertises in this way and therefore are uniquely qualified to carry through the proposed work. Successful demonstration of efficient electron spin injection and high polarisation of output light in a spin-LED at room temperature will be a significant breakthrough for spintronics.
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Organisation Website: http://www.leeds.ac.uk