Aug 20, 2010
In pictures: progress in solid-state lighting
To celebrate recent progress in solid-state lighting, Journal of Physics D: Applied Physics has published a special cluster issue that examines the big issues in LED design from a number of different viewing angles.
Review probes microstructural origins of localization in InGaN quantum wells
The startling success of GaN-based light emitting diodes despite the high density of dislocations found in typical heteroepitaxial material has been attributed to localization of carriers at non-uniformities in the quantum wells (QW) which form the active region of such devices.
Reporting their results in Journal of Physics D: Applied Physics, scientists in the UK have reviewed the different possible structures within the QWs which could act as localization sites, at length scales ranging from the atomic to the tens of nanometre range.
Superior extraction of guided light in embedded PhC LEDs
The enhancement of the extraction efficiency in LEDs through the use of photonic crystals (PhCs) requires a structure that optimizes their interaction with the guided optical modes in the device.
Scientists in the US have investigated three approaches to increasing this interaction - the introduction of an AlGaN optical confining layer, the use of thin-film LEDs and the use of embedded PhCs.
MOCVD delivers high performance InGaN LEDs on Si
Researchers from the Center for Nano-Devices and Systems at Nagoya Institute of Technology, Japan, are taking on the challenge of fabricating InGaN LEDs on silicon. In principle, silicon offers many advantages to developers such as low cost, good thermal conductivity, large wafer size and the option to integrate the device with Si electronics on the same chip. However, there are technical hurdles to overcome.
Using metalorganic chemical vapour deposition, the team has developed high performance InGaN multiple-quantum well (MQW) devices that offer high output power, low operating voltage and low series resistance. What's more, the design is optimized thanks to the insertion of an Al0.06Ga0.94N/GaN strained-layer superlattice underlayer into the structure.