Lateral nanometre structures are highly interesting for future optoelectronic applications, because they should allow the tailoring of device properties by varying device dimensions. As can be shown theoretically, this should lead to improvements in, for example, the band width and the threshold of semiconductor lasers. Up to now, however, no reproducible fabrication technology for these structures exists, so that reliable studies on the properties of quantum wire lasers and modulators are not available. Within the present project, different promising approaches for the fabrication of effectively one- and zero-dimensional structures for optoelectronic devices will be developed. The device-relevant properties will be studied by optical and electrical characterisation techniques. The results of the characterisation will be used for a further optimisation of the technologies.
Lateral nanometre structures are being developed for novel quantum wire lasers and quantum wire modulators by different technologies. In order to assess the potential of the different approaches, the device relevant physical properties of quantum wire and quantum dot structures will be analysed, mainly by optical spectroscopy and model calculations.
By molecular beam epitaxy on V - groove substrates gallium arsenic/aluminium arsenic quantum wires with high quantum efficiencies have been obtained. Lateral superlattices with excellent optical properties were realised on 311 oriented gallium arsenic substrates. By high resolution electron beam lithography and wet etching high quantum efficiency wire structures with lateral widths below 10 nm were realised. Overgrown indium gallium arsenic/indium phosphorus quantum wires were developed by low damage dry etching. The samples were characterized in the different partner laboratories, with regard to quantum efficiencies, lateral subbands, high excitation effects, stimulated emission, phonon spectra and carrier thermalization. By the combination of different spectroscopic techniques available in the partner laboratories of the consortium clear lateral; confinement effects have been observed. The work in the theory groups focused on the calculation of optical transitions, phonons, Raman spectra and electron phonon coupling in quantum wires and dots in close relation with the results of the experimental studies.
APPROACH AND METHODS
The consortium will develop GaAs- and InP-based lateral nanometre structures for optoelectronic applications using novel epitaxy techniques and ultrahigh resolution lithography processes. The basic physical properties of the structures will be investigated by sophisticated characterisation techniques including time-resolved spectroscopy, Raman spectroscopy and magneto-optical experiments. Simultaneously, prototypes for future optoelectronic devices (for example, quantum wire lasers) will be developed and evaluated. The results of the different characterisation techniques will then be used to further optimise the nanometre structure design.
The results of the present investigations should allow the assessment of the potential of low dimensional structures for optoelectronic applications. The high-resolution device patterning techniques developed here for effectively one- and zero-dimensional structures should also be relevant for improved devices based on 2-D structures. The spectroscopic and theoretical investigations will lead to significant improvements of our understanding of the device-relevant physical properties of low dimensional structures. By close interaction with universities, public research institutions and optoelectronic companies, the results of NANOPT will be made available to all relevant European interest groups.
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OX1 3QD Oxford