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Modern Optoelectronics On III-Nitrides

Final Activity Report Summary - MOON (Modern optoelectronics on III-nitrides)

Mainly, the aim of the project is to design, develop and demonstrate new optoelectronic devices in wide-bandgap III-nitrides (modulators and other devices) that embody quantum structures and on-chip integrated parts to realise new photonic functions across the UV-visible. The project is completed successfully as originally planned.

Currently, there has been significant progress in the epitaxial growth and fabrication of III-N compound semiconductors, which offer unique electrical and optical features, offering different possibilities to implement chip-scale UV and visible optoelectronic devices. Eventually, III-N based blue LEDs, blue lasers, and solar-blind detectors have been extensively investigated. Yet, there is still a high potential for different technological applications and commercial use of III-N devices and obviously further research for new optoelectronic devices is required.

The scope of the project has essentially been to fulfil this gap in the III-N device product line and facilitate their technological applications to be commercially used in a wide-scale both for Europe and around the globe.

To this end, we work on the conception, design, fabrication, experimental characterisation, and theoretical modelling of such functional optoelectronic devices and their embedded quantum structures and integrated parts.

For that, in the second year of this project, we designed, grew, fabricated, and demonstrated:
1) UV quantum electroabsorption modulators using a) InGaN/GaN quantum structures in the violet and near-UV and b) GaN/AlGaN quantum structures in the deep-UV;
2) blue quantum electroabsorption modulators based on reversed quantum confined Stark effect with blue shift;
3) blue and cyan quantum electroabsorption modulators for investigation of excitonic effects in polar InGaN/GaN quantum heterostructures;
4) visible (green, blue, violet) light emitting diodes (LEDs) for nanocrystal based hybrid white light generation with tuneable colour parameters;
5) UV (green, blue, violet) light emitting diodes (LEDs) for hybrid white light sources based on layer-by-layer assembly of nanocrystals on near-uv emitting diodes and for white light generation tuned by dual hybridisation of nanocrystals and conjugated polymers.

For the first time, our experimental results showed:
1) demonstration and characterisation of InGaN based n-UV quantum electroabsorption modulators and AlGaN based deep-UV quantum electroabsorption modulators, which also emit light as a second mode of operation when forward bias is applied across the devices;
2) strong electroabsorption behaviour with a blue shift due to the reversed quantum confined Stark effect using blue InGaN/GaN based quantum electroabsorption modulators;
3) strong quantum electroabsorption effect in blue as a result of excitonic effects in polar InGaN/GaN quantum structures and a high absorption coefficient change in blue due to the reversed quantum confined Stark effect;
4) hybridisation of CdSe/ZnS core-shell nanocrystals on InGaN/GaN based visible (blue/near-UV) LEDs and hence, tuneability of colour properties (tristimulus coordinates, colour correlated temperature, and colour rendering index) of the generated light by changing the effects of nanocrystal concentrations and nanocrystal film thicknesses;
5) a) precise control of nanocrystal film thicknesses and order in addition to nanocrystal concentrations by layer-by-layer hybridisation of nanocrystals on near-UV InGaN/GaN LEDs, b) more efficient pumping than blue pumping with UV LEDs c) enhanced white light quality when InGaN/GaN n-UV LEDs are hybridised with different types of CdSe/ZnS core-shell nanocrystals in combination with polyfluorene conjugated polymer.