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EPSRC Reference: EP/C002881/1
Title: The modelling and optimal design of far-infrared quantum cascade lasers for a new generation of Terahertz sources
Principal Investigator: Harrison, Professor P
Other Investigators:
Kelsall, Professor RW Linfield, Professor EH Davies, Professor AG
Researcher Co-Investigators:
Dr D Indjin
Project Partners:
Department: Electronic and Electrical Engineering
Organisation: University of Leeds
Scheme: Standard Research (Pre-FEC)
Starts: 22 June 2005 Ends: 21 December 2008 Value (£): 216,765
EPSRC Research Topic Classifications:
Lasers & Optics Optoelect. Devices & Circuits
EPSRC Industrial Sector Classifications:
Electronics
Related Grants:
Panel History:  
Summary on Grant Application Form
Quantum cascade lasers are unipolar devices that generate monochromaticcoherent infrared radiation. They generate photons through electrontransitions between quantum states in the conduction band ofsemiconductor heterostructures, as the lasers are unipolar, the electron can be recycled and fed into another active region. Thus quantum cascade lasers typically have several tens of active regions allowing a single electron to create more than one photon on its traversal through the device, which leads to high efficiences. In addition, as the transitions all occur within the conduction band, the emission wavelength is independent of the bandgap of the material, hence the quantum cascade laser is a concept transferrable from one material to another. Following the first demonstration of lasing in 1994 in the InGaAs/AlInAs semiconductor system, devices have also been demonstrated in GaAs/AlGaAs and with the promise of integration with CMOS are being developed in SiGe/Si. Development of quantum cascade lasers has continued steadily with the range of wavelengths continually expanding to now cover the 4-24 microns and 70-140 microns regions, the gap is due to the Reststrahlen band in GaAs and is one of the motivating factors for the recent design of GaN/AlGaN devices which could fill the 30-60 microns band.The quantum states are engineered to have favourable properties forlasing by designing the active region of each device as a series oflayers of alternating dissimilar semiconductor materials which formquantum wells. Electrons are introduced to the device through dopingand they occupy states confined in the thin (2-10 nm) quantum wells. A4-level lasing scheme typically requires 4 quantum wells, which in turnimplies 8 semiconductor layers. To recycle the electrons into the nextactive region usually requires another series of 3-5 quantum states andhence another 6-10 semiconductor layers. Thus there are often as manyas 16 semiconductor layers in each period and with as many as 50periods, they are highly complicated devices. This project is focussed on the design of quantum cascade lasers withemission wavelengths greater than 60 microns which is deep in thefar-infrared or Terahertz region of the electromagnetic spectrum. Manymolecular chemicals have absorption lines in this range of frequencieswhich leads to many interesting applications in active securityscanning, chemical and biological sensing, Earth and environmentalmonitoring and medical imaging. The aim of this project is to improveTerahertz quantum cascade lasers, through detailed design andexperimental validation, in order to move them from the laboratory intothis range of applications.
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Organisation Website: http://www.leeds.ac.uk