White light based on blue laser – YAG: Ce3+ phosphor has the advantage of implementing solid-state lighting and optical wireless communications combined-functionalities in a single lamp. However, the blue light was found to disrupt melatonin production, and therefore the human circadian rhythm in general; while the yellow phosphor is susceptible to degradation by laser irradiation and also lack tunability in color rendering index (CRI). In this investigation, by using a violet laser, which has 50% less impact on circadian response, as compared to blue light, and an InGaN-quantum-disks nanowires-based light-emitting diode (NWs-LED), we address both issues simultaneously. The white light is therefore generated using violet-green-red lasers, in conjunction with a yellow NWs-LED realized using molecular beam epitaxy technique, on titanium-coated silicon substrates. Unlike the conventional quantum-well-based LED, the NWs-LED showed efficiency-droop free behavior up to 9.8 A/cm2 with peak output power of 400 μW. A low turn-on voltage of ~2.1 V was attributed to the formation of conducting titanium nitride layer at NWs nucleation site and improved fabrication process in the presence of relatively uniform height distribution. The 3D quantum confinement and the reduced band bending improve carriers-wavefunctions overlap, resulting in an IQE of ~39 %. By changing the relative intensities of the individual color components, CRI of >85 was achieved with tunable correlated color temperature (CCT), thus covering the desired room lighting conditions. Our architecture provides important considerations in designing smart solid-state lighting while addressing the harmful effect of blue light.
Bilal Janjua, Tien K. Ng, Chao Zhao, Dalaver H. Anjum, Aditya Prabaswara, Giuseppe Bernardo Consiglio, Chao Shen, and Boon S. Ooi, "Health-friendly high-quality white light using violet-green-red laser and InGaN nanowires-based true yellow nanowires light-emitting diodes," Proc. SPIE 10104, Gallium Nitride Materials and Devices XII, 101040V (Presented at SPIE OPTO: January 31, 2017; Published: 16 February 2017); https://doi.org/10.1117/12.2250285.
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