Nitrides Seminar - Jake Ewing
Attend in person at ESB 1001!
Zoom option also available
Meeting ID: 889 0013 2164 Passcode: 074242
Graduate Student Researcher, DenBaars Group
University of California, Santa Barbara
V-defect Engineering for Long-Wavelength LEDs
Red and green LEDs have become an increasingly important area of research in the LED industry due to the large number of lighting and display applications. Although InGaN blue LEDs have consistently demonstrated external quantum efficiencies (EQEs) greater than 80%, InGaN green and red LEDs have lagged in efficiency due to high Shockley-Read-Hall (SRH) recombination and trap-assisted Auger recombination (TAAR). In addition, the increased In in the quantum wells at longer wavelengths induce strain related polarization barriers which further decrease LED performance, especially voltage and wall-plug efficiency. These issues result to the “green gap” in visible LEDs.
In the last 5 years, LED researchers have discovered that the strategic use of V-defects can enable lateral injection of carriers into the quantum wells forming “3D p-n diodes”. The lateral injection through the semi-polar V-defect sidewalls reduces the polarization barriers and leads to reduced forward voltage. In this work, we study the structure and formation of V-defects through advanced microscopy. We investigate how V-defect structure, formation and density evolve in growth on (111) Si, flat sapphire, and patterned sapphire. We demonstrate novel ways of forming V-defects and generating the threading dislocations that lead to V-defects. We achieved high EQEs of 6.5% in red LEDs and 30% in green LEDs grown on PSS with V-defect engineering. Furthermore, we showed a 0.9 V reduction at 35 A/cm2 in green LEDs with V-defects compared to a reference green LED with no V-defects. These results and related work from other groups provide a pathway to solving the green gap through V-defect engineering and increase the scientific understanding of threading dislocation and V-defect formation in GaN epitaxy.