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The Nanostructures Laboratory was set up in the Autumn of 1987 as part of the Nanoelectronics Research Centre of the University of Glasgow, to carry out research in the underlying science of optical processes in semiconductor nanostructures, i.e., device-relevant science.
From the beginning the work of the laboratory has had a pioneering character in this field with many achievements, which began with the first observation of surface phonons in GaAs cylinders in 1988. A selection of publications below provides a flavour of our activities so far.
The experiments which are possible include photoluminescence, photoluminescence excitation, absorption, Raman scattering, resonant Raman scattering, photoreflectance, high pressure electrical and optical experiments, magneto-optics, magneto-transport and deep level transient spectroscopy (DLTS).
The laboratory is equipped with a U1000 1m double spectrometer, a THR1000 single 1m spectrometer, and two other smaller monochromators. Excitation sources include a 20W Argon laser with UV option, a 6W Argon laser, and a home-made Ti-Sapphire laser. A range of cryostats is available for work from 1.6 to 300K in several bore sizes, for both optical and electrical work. The detectors cover the range from 300 nm to 1.5 mm and use single and multichannel detection. There are two optical diamond anvil cells (one non-magnetic) to acjieve pressures up to 10 GPa, and two electrical high pressure cells for 4-300K operation up to 1.5 GPa. Signal processing electronic equipment for electrical measurements such as variable temperature Hall and Shubnikov-de Haas are available in fields up to 8T. There is a 6.7 T split-coil variable temperature magnet for magneto-optical experiments. Data acquisition is computerised. DLTS measurements are performed in a Biorad system.
The Laboratory is part of the Nanoelectronics Research Centre and as such the work in it benefits from a supply of high quality MBE GaAs and GaInAs-based quantum wells, together with access to state-of-the-art lithography and dry etching for the fabrication of nanostructures down to 15 nm nanostructures. Access to high resolution SEM allows a preliminary structural image of the nanostructures to be obtained. The laboratory works on III-V, II-VI and IV-IV semiconductor compounds, where the provision of non-III-V materials comes from our collaborators.
More recently the laboratory is working in closer collaboration with the Optoelectronics Research Group at Glasgow on photonic bandgap materials.
The funding of the experimental work comes mainly from the UK Engineering and Physical Science Research Council, from small grants for collaborative work from the British Council and NATO, INTAS and from the European Union ESPRIT programme. Collaborative work can also be undertaken, on a commercial basis, through Kelvin Nanotechnology.
Professor Fred H Pollak, Brooklyn College of the City University of New York, on modulation spectroscopy of nanostructures. Dr Nikolai N Ledentsov and Professor Sergei A Permogorov, A F Ioffe Physico-Technical Institute of St Petersburg, on corrugated superlattices, fractional monolayer structures, wide-gap II-IV's, energy relaxation and localisation. Dr Gaspar Armelles, National Centre for Microelectronics, Madrid, on phonons in nanostructures. Dr Sergei Romanov, A F Ioffe Physico-Technical Institute of St Petersburg, on optical properties of semiconductor zeolites. Dr David Lockwood and Pawel Hawrylak, National Research Council in Ottawa, on Raman scattering and theory of many body effects in nanostructures. With Prof E H C Parker, University of Warwick, on Si-SiGe nanostructures. Prof Bernard Lunn and Dr D E Ashenford, Hull University, on CdMnTe-CdTe nanostructures. Prof Bennet Goldberg, Boston University, on Near Field Optical Microscopy of nanostructures. Dr Jean Lascaray of Univ Montpellier II, on wide-gap II-VI nanostructures. Dr Hans-Peter Wagner, Regensburg University, on waveguides in ZnTe-ZnSe. Dr Phil Dawson, UMIST Manchester, on time-resolved luminescence. Prof BRuce McCombe, State University of New York at Buffalo on far infrared measurements in quantum wires. Prof G Bauer, University of Linz, on high resolution X-ray diffractometry. Dr W-X Ni, Linköping University on electroluminescence of Si-SiGe quantum dots. Prof H-J Wolter, Technical University of Eidhoven, on four-wave mixing in InAs buried quantum dots. Dr W Ge, Hong Kong University of Science and Technology on wide-gap II-VI. Dr W Kinssinger, Institute of Semiconductors GmbH at Frankfurt-Oder on Si-SiGe. Profs B Joyce and G Parry, Interuniversity Research Centre on Semiconductors at Imperial College London, on Si-SiGe. The Centre for Electronic Materials at UMIST Manchester on semiconductor-filled zeolites and silicates. Dr Kevin Prior, Heriot Watt university in Edinburgh, on electrical pumping of II-VO lasers using nanovalves.
The laboratory has had fruitful collaborations in the past with Prof C Weisbuch Dr Henri Benisty (Palaseau), Prof Jordi Pascual (Barcelona), Dr T Suski and Dr Iza Gorczica (UNIPRESS, Warsaw), Prof M Razeghi (Northwestern University) and many other groups in the UK.
1989 M Watt, Inelastic Light Scattering in Low Dimensional Semiconductors
1989 I T Ferguson, Optical properties of GaAs-based novel Semiconductor Structures
1993 W E Leitch, On the Luminescence Intensity of Quantum Dots, Dashes and Wires
1993 W O S Rodden, A Study of the Optical Properties Semiconductor Microcrystallites
1993 H Zhou, High Pressure Studies of Low Dimensional Structures
1993 R W MacLeod, Excitons and Phonons in GaInAs-InP Quantum Dots and Wires
1995 A P Smart, on II-VI nanostructures: Fabrication and Chracterisation
Some questions driving the research of the laboratory
(a) What is the difference between the lateral sizes felt by the quasi-particles in quantum dots and wires, compared to the physical dimensions, and how does this difference affect optical processes.
(b) Are there side-effects arising from the fabrication process and if so, what is their nature and how can we control them and/or account for them
c) Is the phonon bottleneck controlling the emission across the gap in wires and dots, and if so how can we bypass it for light emitting devices?. Conversely, how can we enhance the bottleneck effect for infrared active devices?
d) How are energy and momentum relaxation processes modified by the reduction in lateral dimensions?
e) Does exciton transport play a role in 1-D quantum wire laser performance and if so what are the mechanisms at play?
f) How is the phonon spectrum of nanostructures modified in comparison with the existing theories of phonons in 1-and 0-D?
g) What role can alternative nanostructures (e.g. directly grown, zeolites, etc) play in the development of 1- and 0-D future devices
h) How is the electron (exciton) - phonon interaction modified in nanostructures and what is the impact on carrier cooling and electro-optical properties?
i) What are the prospects of using quantum dots to simulate an analogue-like device operated by electrons or photons?
j) How to optimise electroluminescent devices based on Si-SiGe quantum dots for optical interconnects.
k) How efficient are opal matrices filled with semiconductors as 3D photonic bandgap materials?
M Watt, C M Sotomayor Torres, H E G Arnot and S P Beaumont, Surface Phonon Modes in GaAs Cylinders, Semicond Sci Technol 5, 285-290 (1990)
H Benisty, C M Sotomayor Torres and C Weisbuch, An Intrinsic Mechanism for the Poor Luminescent Properties of Quantum Box Systems, Phys Rev B44, 10945-10948 (1991)
P D Wang, C M Sotomayor Torres, H Benisty, C Weisbuch and S P Beaumont, Radiative Recombination in GaAs-AlGaAs Quantum Dots, Appl Phys Lett 61, 946-948 (1992)
Y S Tang, C D W Willkinson, C M Sotomayor Torres, D W Smith, T H Whall and E H C Parker, Optical Properties of Si/Si1-xGex Heterostructure Based Wires, Solid State Commun, 85 (3), 199-202, 1993
P D Wang and C M Sotomayor Torres, Phonon Raman Scattering in GaAs-based Quantum Dots, Solid State Communications 88 (1) 63-66 (1993)
P D Wang and C M Sotomayor Torres, Multiple phonon relaxation in GaAs-gaAlAs quantum well dots, J Appl Phys 74, 5047 (1993)
C M Sotomayor Torres, A P Smart, M Watt, M A Foad, K Tsutsui and C D W Wilkinson, Nanometer fabrication techniques for wide-gap II-VI semiconductors and their optical characterisation , J Electronic Materials 23, (3), 289-298 (1994)
H Qiang, F H Pollak, Y S Tang, P D Wang and C M Sotomayor Torres, Characterisation of process-induced strains in GaAs/GaAlAs quantum dots using room temperature photoreflectance, Appl Phys Lett 64 (21) 2830-2832 (1994)
P D Wang, N N Ledentsov, C M Sotomayor Torres, I N Yassievich, A Pakhomov, A Yu
Egorov, P S Kopev and V M Ustinov, Magneto-optical properties in ultrathin InAs-GaAs quantum wells, Phys Rev B 50 (3) 1604-1610 (1994)
G Gumbs, D Huang, H Qiang, F H Pollak, P D Wang, C M Sotomayor Torres and M C Holland, Electromodulation Spectroscopy of an array of GaAs/GaAlAs Quantum Dots: Experiments and Theory, Phys Rev B 50 (15) 10962-10969 (1994)
W O S Rodden, C M Sotomayor Torres and C N Ironside, Three Dimensional Phonon Confinement in CdSe Microcrystallites in Glass, Semicond Sci Technol 10, 807-812 (1995)
M V Belousov, N N Ledentsov, M V Maximov, P D Wang, I N Yasievich, I A Kozin, V M Ustinov, P S Kop'ev and C M Sotomayor Torres, Energy levels and oscillator strength in submonolayer InAs-GaAs heterostructures, Phys Rev B 51 (20) 14346-14351 (1995)
G Armelles, P Castrillo, P D Wang, C M Sotomayor Torres and N N Ledentsov, Study of the interface of (311) oriented GaAs/AlAs superlattices by Raman Scattering, Solid State Commun 94 (8) 613-617 (1995)
H F Ghaemi, B B Goldberg, C M Sotomayor Torres, P D Wang, M Fritze, A Nurmikko, Spectroscopy of Individual Quantum Structures with Low Temperature Near Field Optical Microscopy, to appear in Superlattices and Microstructures
Y-S Tang, WX Ni, C M Sotomayor Torres and G V Hansson, Enhanced room-temperature electroluminescence from Si-Si0.7Ge0.3 quantun dot diodes, Elec Lett 31 (16) 1386-1387 (1995)
If you would like to know more about the research activities of the laboratory, please contact Dr Clivia M Sotomayor Torres at the address above.
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