title: Improved photoluminescence efficiency in UV nanopillar light emitting diode structures by recovery of dry etching damage.
abstract: In this study, we have fabricated 375-nm-wavelength InGaN/AlInGaN nanopillar light emitting diodes (LED) structures on c-plane sapphire. A uniform and highly vertical nanopillar structure was fabricated using self-organized Ni/SiO2 nano-size mask by dry etching method. To minimize the dry etching damage, the samples were subjected to high temperature annealing with subsequent chemical passivation in KOH solution. Prior to annealing and passivation the UV nanopillar LEDs showed the photoluminescence (PL) efficiency about 2.5 times higher than conventional UV LED structures which is attributed to better light extraction efficiency and possibly some improvement of internal quantum efficiency due to partially relieved strain. Annealing alone further increased the PL efficiency by about 4.5 times compared to the conventional UV LEDs, while KOH passivation led to the overall PL efficiency improvement by more than 7 times. Combined results of Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) suggest that annealing decreases the number of lattice defects and relieves the strain in the surface region of the nanopillars whereas KOH treatment removes the surface oxide from nanopillar surface.
authors.affiliation: School of Advanced Materials Engineering and Research Center of Advanced Materials Development, Chonbuk National University, Jeonju 561-756, Korea.
authors.forename: Dae-Woo
authors.initials: DW
authors.lastname: Jeon
authors.forename: Lee-Woon
authors.initials: LW
authors.lastname: Jang
authors.forename: Ju-Won
authors.initials: JW
authors.lastname: Jeon
authors.forename: Jae-Woo
authors.initials: JW
authors.lastname: Park
authors.forename: Young Ho
authors.initials: YH
authors.lastname: Song
authors.forename: Seong-Ran
authors.initials: SR
authors.lastname: Jeon
authors.forename: Jin-Woo
authors.initials: JW
authors.lastname: Ju
authors.forename: Jong Hyeob
authors.initials: JH
authors.lastname: Baek
authors.forename: In-Hwan
authors.initials: IH
authors.lastname: Lee
mesh_terms: D003890:Desiccation / Q000379:methods; D004867:Equipment Design; D019544:Equipment Failure Analysis; D008029:Lighting / Q000295:instrumentation*; D008163:Luminescent Measurements / Q000295:instrumentation*; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D010316:Particle Size; D012666:Semiconductors; D014466:Ultraviolet Rays