Semi-polar planes to boost LED light efficiency
Holding great promise for lower energy consumption and high conversion efficiencies, lighting fixtures with solid-state light sources have the potential to change the dynamics of the global lighting market. Despite their great promise, LEDs rapidly drop off in efficiency as the driving current is increased. Driving LEDs efficiently at high currents should have a positive impact on cost and performance. Semi-polar GaN, combined with low-defect density substrates, enables significant improvements in optical efficiency compared to conventional polar GaN devices. Results from the ALIGHT (AlGaInN materials on semi-polar templates for yellow emission in solid state lighting applications) project could herald a breakthrough in semi-polar GaN LEDs. Researchers have demonstrated large-scale semi-polar GaN LEDs that efficiently emit light from the blue to the yellow colour spectrum. The semi-polar GaN epitaxial layers were grown on r-plane sapphire and silicon wafers of 100 mm in diameter. The team believes that this is the first successful effort of growing such large semi-polar GaN templates. Except for LEDs, these large-diameter wafers can serve as a basis for developing new types of sensors and electronic devices. Compared to commercial LEDs grown on the c-plane, this semi-polar version exhibits higher quantum efficiency at high current densities and emits polarised light. Growing GaN films in different crystal orientations in addition to growing quantum well structures with high levels of doping helped reduce polarisation-related internal electric fields that typically limit performance of conventional GaN-based LEDs. ALIGHT advances in light-emitting efficiency at high currents can significantly accelerate the widespread uptake of LED technology. Semi-polar GaN-based LEDs exhibit excellent colour rendering and improve performance in the blue and yellow spectral regions – quantum efficiencies can exceed 70 % in the blue and 35 % in the yellow wavelengths.
Keywords
Semi-polar, LED, light sources, GaN, lighting, high currents, ALIGHT, quantum efficiency
