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Research Overview
The group is concerned with the study of the optical, electronic and vibrational properties of a wide range of bulk and low dimensional semiconductor structures and devices. Experimental methods include photoluminescence (PL), electroluminescence (EL), photoluminescence excitation (PLE), photocurrent, (PC) and ultrafast spectroscopy, together with reflection, Raman scattering, magneto-optical and transport studies.
For laser experiments the group has several Ar+ lasers (1 × 20W and 2 × 6W), also a HeCd laser with both blue & UV mirrors and a (visible) dye laser. Ultrafast experiments are carried out with our three femtosecond Ti:sapphire laser systems. A femtosecond OPA gives continuous tunability from 200nm in the ultraviolet to 18 microns in the infrared.
In regular use are the HeNe lasers and the two CW Ti:sapphire (IR) lasers which are ideal for energy probing measurements in III-V materials such as GaAs/AlGaAs. Other optical sources are a Xe lamp and various other halogen lamps. Our laser devices programme deals primarily with electrically pumped semiconductor devices (either cascade or quantum dot).
Sample cooling can be achieved in numerous cryostats for both liquid-He and liquid-N2 temperature. The smallest microstats provide good angular access required for work on photonic bandgap (PBG) crystals. A 16T superconducting magnet is available for optical transport and magnet-optic experiments. A diamond anvil cell allows optical spectroscopy to be performed up to pressures of 10 GPs. The diversity of experiments undertaken by the group means that we have a large amount of the general purpose optical equipment in use. Experiments take place over a wide range of wavelengths from the ultraviolet (for nitrides) to the far infrared (as for cascade lasers). Of our more sophisticated apparatus we have several micro-PL (µPL) benches for work on single quantum dots and micropillars, and also a stimulated scattering rig for investigation of microcavities. The µPL cryostats can be combined with our ultrafast lasers for coherent control and Hanbury Brown-Twiss experiments.
Our detection equipment includes: double grating 0.85m spectrometer, triple spectrometer, 0.75m single spectrometer, 0.46m single spectrometer, 3 minimate spectrometers, far-infrared Fourier transform (FTIR) system and a brand-new 0.60m single spectrometer; The detectors that are in common use are 3 CCD-cameras, 5 Ge-detectors (all liquid-N2 cooled), and 2 photomultiplier tubes.
Many of the above projects and publications are joint ones with members of the Electronic and Electrical Engineering Department. This department houses the Engineering and Physical Sciences Research Council (EPSRC) Central Facility for III-V Semiconductors where the majority of our structures and devices are grown and fabricated. This facility contains two MBE reactors for the growth of GaAs and InP based materials and two MOVPE reactors for the growth of similar materials. The Facility has recently been awarded funds for a new reactor to grow wide band gap, nitrogen based semiconductors.
Our group has many active collaborations with other research groups, both in universities and industry, in this country and abroad. Present contacts include: University of Nottingham, Cambridge University, Oxford University, University of Southampton, University of St Andrews, Heriot-Watt University, University of Bristol, University of Wales at Cardiff, PRP Optoelectronics Towcester, Epitaxial Products International Cardiff, Defence Evaluation and Research Establishment Great Malvern, Toshiba Research Laboratories Cambridge, Technical University of Berlin, Solid State Institute Israel, Hong Kong University of Science and Technology.
