ALIGHT

AlGaInN materials on semi-polar templates for yellow emission in solid state lighting applications

 Partecipanti

Mappa

 Word cloud

Esplora la "nuvola delle parole (Word Cloud) per avere un'idea di massima del progetto.

 Obiettivo del progetto (Objective)

'With up to 20% of electrical energy being consumed by lighting, it is important to use this energy wisely. Replacing the inefficient light generation technologies of today with solid state lighting based on gallium nitride (GaN) light emitting diodes (LEDs) will enable us to reduce this 20% to 10% or even 5%. However, several factors need to be addressed to accelerate the uptake of this emerging technology. These are obtaining an acceptable and controllable colour from the lighting units while reducing the capital cost through large scale process technologies. This project proposes the development of AlGaInN materials and structures to achieve much higher efficiencies at blue-green and yellow light wavelengths enabling highly luminous and controllable light generation. The approach in this proposal is based on reducing the internal electric fields in the light emitting quantum well material through the development of semi-polar GaN templates on large area sapphire and silicon substrates. The growth process development and optimisation will be informed by modelling of the surface reactions and through timely and detailed characterisation of the material properties. Growth of quantum dots within a quantum well in a low electric field environment will allow internal quantum efficiencies to reach >70% in the blue and >35% in the yellow spectral regions. The material quality will be verified in demonstration LEDs which will be benchmarked against current devices. Issues around the scaling of the technology to a manufacturing environment and 100 mm diameter substrates will be addressed. This approach can lead ultimately to efficacies of over 200 lumens/W with colour rendering indices >90%. European science will benefit through the new knowledge, while European industry can be more competitive by adopting the new processes and the European citizens will benefit from a higher quality of light in their everyday environment and reduce drastically the costs for lighting.'

Descrizione progetto (Article)

Holding great promises for lower energy consumption and high conversion efficiencies, lighting fixtures with solid-state light sources have the potential to revolutionise the lighting industry. Further advances in light-emitting efficiency at high currents, with excellent colour rendering at low cost would significantly accelerate the widespread uptake of this technology.

The EU-funded project http://www.alight-project.eu/ (ALIGHT) (AlGaInN materials on semi-polar templates for yellow emission in solid state lighting applications) is investigating the materials for these improved lighting devices by developing new large-area semi-polar templates using sapphire and silicon substrates. These semipolar templates help reduce the inbuilt electric fields in LEDs which affect their colour stability and efficiency and provide a large area, low cost platform for the growth of the LED layers. The project is also using the indium aluminium gallium nitride (InAlGaN) material for the light-emitting layers, targeting blue and yellow emission.

A major challenge is patterning of the wafer to generate and coalesce semi-polar planes on the structured sapphire substrate. To this end, scientists are evaluating the impact of substrate fine orientation and growth parameters through X-ray measurements, luminescence and atomic-scale imaging. Metalorganic and hydride vapour phase epitaxy (MOVPE and HVPE, respectively) are used to grow layers on the substrates. The active light-emitting material consists of quantum wells that have high optical efficiency and excellent colour purity.

Over the first project period, scientists performed significant work with regard to growing semi-polar GaN templates using different approaches.

Project partners used the HVPE technique to overgrow GaN on top of a GaN layer grown by MOVPE that was initially prepared on pre-structured sapphire. InGaN layers were then grown on semi-polar GaN templates with different growth temperatures. Semi-polar InGaN structures with different thicknesses were optimised, reaching high conversion light-emitting efficiencies in the blue and yellow spectra.

A move from growing devices on semi-polar substrates is helping to overcome issues related to reduction in LED light-emitting efficiency. Replacing current lighting technologies with solid-state lighting based on InGaN LEDs should enable a reduction in electricity by up to 5 %.