design of monolithic white led with ingan/gan/ingan mqws · led devices are becoming cheaper – 50...
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Design of Monolithic White LED with InGaN/GaN/InGaN MQWsShreyas DmelloMaster of Engineering, Electrical Engineering
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▪ White light generation
– RGB LED
– High energy + phosphor coating
▪ “White” LEDs have poor Color Rendering
Index
– Green Gap
– Phosphor emission is limiting
▪ Applications favor high luminosity + CRI
– Safety considerations
– Aesthetics
▪ Goal: Want 6000K “White” LED
Problem & Motivation
Source: Westinghouse Lighting CRI-Color Rendering Index
Source: ADV Pulse Cyclops Headlights
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▪ Monolithic Device
– MQW Structure
– Blue + Yellow = White!
▪ GaN/InGaN structures
– Wide emission range
– Similar lattice constants (3.54-
InN vs 3.19-GaN)
▪ Band Engineering
– Control barrier height
– Control color temperature!
Device Structure
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Source: Light Emitting Diodes, E. F. Schubert
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▪ Maintains basic LED physics
– High efficiency
– IV curve is standard
▪ Confirms hypothesis
– Barrier height is linked with
carrier filling
– Changing one barrier layer,
changes output emission
Simulation Results
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▪ CIE 1931 Color Space
– Visual representation of spectrum
– Takes into account human eye responses
▪ 6000 K is perfect sunlight
– Actual temperature is opposite
descriptors
– Bluer emission is “cooler”
– Reddish emission is “warmer”
▪ Monolithic structure was close!
– 0% In comp. – cool (8372 K)
– 1% In comp. – neutral (5914 K)
– 2% In comp. – warm (4649 K)
Color Accuracy
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Source: mat.univie.ac.at –CIE Chromaticity Diagram
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▪ Monolithic “White” LED is possible!
– Research groups investing in this tech
– Design constrains limited emission
– Slight blue shift in current design
▪ Pros vs. Cons:
– Pro - No phosphor
– Pro - Single structure
– Con - Costly to manufacture
– Con - Efficiency vs. color balance
▪ LED devices are becoming cheaper
– 50 years prior vs. 50 years to the future
– Manufacturing process improvements
Conclusions
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Source: White Emission from InGaN MQW on c-planes and nano-pyramid hybrid structures, Kim et al.
Source: LEDinside – LED Price Trends
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