Light extraction efficiency and internal quantum efficiency of fully UVC-transparent AlGaN based LEDs. (4th June 2021)

• Record Type: Journal Article
• Authors: Guttmann, Martin; Susilo, Anna; Sulmoni, Luca; Susilo, Norman; Ziffer, Eviathar; Wernicke, Tim; Kneissl, Michael
• Is Part Of: Journal of physics. Volume 54:Number 33(2021)
• Publication Date: 2021-06-04
• Subjects: deep UV LED -- AlGaN -- reflective contact -- ray-tracing simulation -- light extraction efficiency; Physics -- Periodicals; 530
• DOI: 10.1088/1361-6463/ac021a
• Languages: English
• ISSNs: 0022-3727

Abstract

Abstract: The light extraction efficiency (LEE), external quantum efficiency (EQE), and current–voltage characteristics of deep ultraviolet light emitting diodes (DUV-LEDs) with different aluminum mole fractions in the p-AlGaN layers have been investigated. Optimizing the p-AlGaN layer composition requires a tradeoff between reducing the absorption losses and limiting the increases in the p-contact resistance and operation voltage. AlGaN multiple quantum well LEDs emitting around 263 nm with different AlGaN:Mg short period super lattices (p-SPSL) ranging from x = 33% (UV-absorbing) to x = 68% (UV-transparent) average aluminum mole fraction have been explored. DUV-LEDs with different p-contact metals and UV-reflectivities have been characterized by electroluminescence measurements and analyzed by ray-tracing simulations. The comparison shows an increased operating voltage and a five-fold increase of the on-wafer EQE with a maximum value of 3.0% for DUV-LEDs with UV-transparent p-SPSL ( x = 68%) and UV-reflective indium contacts in comparison to LEDs with a UV-absorbing p-SPSL ( x = 33%). Ray-tracing simulations show that the increase in EQE can be partially ascribed to a 2.5-fold improved LEE in combination with a two-fold increase in internal quantum efficiency.