Abstract
We demonstrate a phosphor free, dichromatic GaN-based monolithic white LED with vertically stacked green and blue emitting multiple quantum wells. The optimal thickness of GaN barrier layer between green and blue quantum wells used is 8 nm. This device can be tuned over a wide range of correlated color temperature (CCT) to achieve warm white (CCT = 3600 K) to cool white (CCT = 13,000 K) emission by current modulation from 2.3 A/cm2 to 12.9 A/cm2. It is also demonstrated for the first time that a color rendering index (CRI) as high as 67 can be achieved with such a dichromatic source. The observed CCT and CRI tunability is associated with the spectral power evolution due to the pumping-induced carrier redistribution.
Highlights
White LEDs based on InGaN are used in many applications from backlighting to mobile displays and general illumination [1,2,3]
We demonstrate phosphor free, color tunable monolithic white LED
The current–voltage (I-V) characteristic under continuous wave (CW) regime at 300 K was studied for the LEDs from the same wafer
Summary
White LEDs based on InGaN are used in many applications from backlighting to mobile displays and general illumination [1,2,3]. A multichip approach with vertical or lateral combination of blue, green and red LEDs can be used for white light generation This approach requires complex fabrication procedures, driving circuits, and device design, thereby affecting reliability and increasing production cost [2]. 3.5 eV by indium (In) variation in InGaN QWs, is being explored [8,9,10,11] This all semiconductor monolithic approach holds potential of efficient color tunable sources with high CRI. Nguyen et al have reported color tunability and CRI values more than 90 for “dot in a wire” core shell LEDs on silicon [13] This approach requires a complex growth and fabrication process with precise control over wire diameter and dot size, which is not ideal for mass production. It is shown that CRI of over 60 can be demonstrated with these devices and CCT of emission in such LEDs can be tuned by modulation of pumping current
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