Quantised Electronics


QUANTECS - 6312

Work Area: Nanoelectronics

Keywords nanostructures, nanotechnology, quantum dots, quantum wires, quantum optics


Start Date: 1 October 92 / Duration: 36 months / Status: running

[ participants / contact ]


Abstract QUANTECS is studying devices and physical phenomena with potential application in the processing, storage and transmission of information using single electrons and photons. Topics include nanometre-scale device fabrication, electron confinement technology, single-electron transport devices, and the controllable emission of single photons. The work builds on the results of NANSDEV (3133).


Aims

The objective of the QUANTECS Working Group is the study of devices and physical phenomena that may, in the long term, lead to the processing, storage and transmission of information using single electrons and photons.

Topics of interest to members of the Group include: the fabrication of devices with nanometre-scale dimensions in which single electron effects can be detected; improvements in the technology of electron confinement, in order to raise the temperature of observation of single-electron effects; the fabrication and understanding of devices in which electrons can be moved from point to point in the manner of cellular automata, and also in which artificial bandstructures might provide additional flexibility in controlling such transport (the use of scanning tunnelling microscope (STM) fabrication techniques could well be important here). The consortium is also interested in devices that may ultimately allow single photons to be controllably emitted. These are related to quantum dot structures, where fundamental questions still arise concerning the physical mechanisms which control the emission of light. The answers to these questions may determine the field of application of quantum dots as efficient emitters, or efficient absorbers, of light.

Activities

The Group's expertise ranges from nanometre-scale technology to low-temperature physics and optical spectroscopy, and embraces all the disciplines currently known to be of importance to its goals. Research being carried out by the group covers a broad base; consequently, smaller teams have been established to tackle specific areas. The Group will further its objectives through its own internal contact network which, depending upon the topic in question, will involve meetings of two or more partners. The group meets at six-monthly intervals to discuss scientific progress and to formulate responses to calls for proposals, and also promotes short exchanges of personnel between partners to further research of mutual interest. It has close associations with the PHANTOMS network of excellence (7360) and participates in workshops involving other ESPRIT nanoelectronics consortia (6536, 6719, 6489, 7227).

Progress and Results

Significant progress has been made towards increasing electron confinement and raising the temperature of operation of quantum transport devices. Using shallow two-dimensional electron gas structures, quantised conductance in point contacts has been observed at temperatures well above 4K. Lateral superlattice devices fabricated on this material are affected by the strain induced by differential contraction between semiconductor and gate metal; and in antidots made on these substrates, it is possible to detect ballistic electron orbits around 1, 2, 4, 9 and more antidots. Quantum wires induced by gate potentials in undoped heterojunction substrates show very strong capacitance oscillations which reflect the population of one-dimensional sub-bands, again at 4K but this time over very large areas. These results point to the importance of strong confining potentials and the smoothness of those potentials in the fabrication of extended quantum devices. In vertical transport devices (resonant tunnelling diodes), we have shown that fluctuations at the onset of current are associated with the existence of zero-dimensional states which are associated with donor impurities. In small area p-i-n resonant tunnelling diodes, red shifts in the electroluminescence are associated with a reduction in device dimension below 1 micron. New methods of fabricating quantum dots using selective etching techniques have been demonstrated. Very high finesse (>5000) Fabry-Perot microcavities have been realised in the GaAs/AlGaAs system, and an experimental system to measure the optical properties of these structures is being assembled. Further studies of luminescence from quantum dots and wires continue to accumulate evidence for the phonon bottleneck model of luminescence quenching, and progress is being made towards the fabrication of quantum wires in V-grooves by MOCVD.

Potential

Application of the technology of shallow two-dimensional electron gases in high-speed devices is already in progress. Undoped devices are also applicable in high-speed electronics, and extended quantum wires offer the possibility of fabricating far infra-red detectors. The electroluminescence from small p-i-in RTDs is important for the possibility of quantum dot LEDs, and the fabrication of quantum dots together with the study of their transport properties is a step towards the exploitation of single-electron effects. Work on optical microcavities is expected to have impact on the development of high brightness LEDs because of the improved directionality of the output beam and better output coupling efficiency.

Latest Publications

Information Dissemination Activies

Members of the working group are regular participants in the major international conferences in this field. QUANTECS was well represented at the ESPRIT Basic Research Symposium on Nanoelectronics held in Brussels in November 1992, and at the PHANTOMS workshop held in Wurzburg in October 1993.


Coordinator

University of Glasgow - UK
Nanoelectronics Research Centre
Dept. of Electronics and Electrical Engineering
UK- Glasgow G12 8QQ

Participants

IMEC vzw - B
EPFL - CH
Ludwig Maximilians Universität - D
Centro Nacional de Microelectronica (CNM) - E
Thomson CSF - F
Nederlandse Philips Bedrijven - NL
Technische Universiteit Delft - NL
University of Lund - S
University of Nottingham - UK

CONTACT POINT

Prof. S. Beaumont
tel +44/ 41-3305380
fax +44/ 41-3304907
e-mail: spb@nano.gla.ac.uk


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QUANTECS - 6312, August 1994


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html version of synopsis by Nick Cook