Apr 5 (Mon): "Design and application of compliant III-nitride substrates using Porous GaN," Shubhra S Pasayat, ECE PhD Defense
The invention of blue LED revolutionized the lighting and display industry owing to their high energy efficiency. In displays, their use has been limited to backlight units of LCDs, relying on yellow phosphors for white light emission, then using color filters to produce RGB primary colors, resulting in ~5% efficiency. Self-emissive light emitters like organic LEDs (OLEDs) are the most premium displays on market currently due to their ability to produce high contrast images. However, these displays degrade over time due to their organic nature and are only about 10-20% efficient. Self-emissive inorganic micron-sized LEDs or micro-LEDs are considered the next in line display technology with theoretical efficiency limit of about 60%. The materials of choice for inorganic RGB micro-LEDs are Indium Gallium Nitride or InGaN for blue and green emission, and Aluminum Gallium Indium Phosphide or AlInGaP for red emission. For cost-effectiveness, these micro-LEDs much be scaled to dimensions below 10 microns while maintaining high efficiency, which is difficult for AlInGaP based LEDs. This has motivated the exploration of dimensionally scalable red emitting inorganic materials.
InGaN based materials can emit in the red regime with a higher indium content in the InGaN/GaN quantum wells, but they suffer from lattice mismatch induced low efficiency. We targeted the reduction of this misfit strain using a flexible porous GaN based substrate technology and achieved device level demonstrations, with potential application in AlGaN based devices as well. In this defense, I will discuss the conceptualization, fabrication and optimization of the strain relaxed substrates followed by process optimizations which led to our demonstration of world’s first <10 μm sized red LED with measurable efficiency.
Shubhra S Pasayat received her B.Tech. degree in Electronics and Electrical Communications Engineering from Indian Institute of Technology (IIT) Kharagpur in 2013 and worked at Samsung R&D Institute as a Senior Hardware Engineer till 2015. She joined the University of California Santa Barbara (UCSB) in 2015 to pursue her master’s and Ph.D. in Electrical and Computer Engineering. As a Graduate Student Researcher, she is currently working on ultrasmall (< 10 μm sized) InGaN-based micro-LEDs emitting in yellow, orange, and red regime.
Hosted by: Professor Umesh Mishra
Submitted by: Shubhra S Pasayat