Graded Index Transparent Conducting Materials with Enhanced Optical Functionality

Abstract

Transparent conducting oxides (TCO) have been extensively used in various technologically important applications including solar cells, flat panel displays, antireflective coatings, (organic)light emitting diodes and many other uses as advanced optical materials. Nanoporous and nanostructured films, assemblies and arrangements are important from an applied point of view in microelectronics, photonics and optical materials.The ability to minimize reflection, control light output and use contrast and variation of the refractive index to modify photonic characteristics can provide routes to enhanced photonic crystal devices, omnidirectional reflectors, antireflection coatings and broadband absorbing materials.This work demonstrates very high quality epitaxially grown (MBE) indium oxide, and indium tin oxide nanostructures and nanowires that are defect free and grown using homogeneous ITO seeds from glass or semiconducting surfaces. These branched and graded porosity layers grown directly on LEDs, glass coatings and other devices are shown to significantly enhance transparency or absorbance, depending on the visible wavelength range of interest and suppress Fresnel reflections for antireflection coatings. The benefit of controlling optical properties of nanoporous transparency conducting materials are shown for SiGe MQW LEDs, transparent Li-ion battery electrodes, antireflection coatings, and selective frequency absorbers across the visible range, and also demonstrates control over IR transmission without adversely affecting electronic conductivity.ReferencesC. M. Eliason and M. D. Shawkey, Optics Express, 22 A642 (2014).C. O'Dwyer, M. Szachowicz, G. Visimberga, V. Lavayen, S. B. Newcomb and C. M. S. Torres, Nature Nanotech., 4, 239 (2009).C. O'Dwyer and C. M. S. Torres, Front. Physics, 1, 18 (2013).M. Osiak, W. Khunsin, E. Armstrong, T. Kennedy, C. M. S. Torres, K. M. Ryan and C. O'Dwyer, Nanotechnology, 24, 065401 (2013).M. Osiak, E. Armstrong, T. Kennedy, C. M. S. Torres, K. M. Ryan and C. O'Dwyer, ACS Appl. Mater. Interfaces, 5, 8195 (2013).P. D. C. King, T. D. Veal, J. Phys. 23, 334214 (2011).J. Q. Xi, M. F. Schubert, J. K. Kim, E. F. Schubert, M. Chen, S. Y. Lin, W. Liu and J. A. Smart, Nature Photonics, 1, 176 (2007).