High Efficiency Nanostructured Light Emitting Diodes on Nonpolar Substrates

North Carolina State University, Raleigh NC

Investigators

Abstract

The objective of this research is to enhance the quantum efficiencies (IQE) of GaN based light emitting diodes (LEDs) to be used for solid state lighting closer to 100%. The approach is to reduce harmful defects in device layers and enhance photon generation and create better Ohmic contacts to enhance photon extraction. The proposed research addresses four critical scientific issues in enhancing IQE (LEDs). These critical thrusts include: (1) thin film epitaxy across the misfit scale on nonpolar (r-plane) sapphire; (2) management of stresses and charge through control of defects and interfaces; (3) nanostructured thickness variation or quantum confinement of active carriers, and (4) formation of low-resistivity transparent Ohmic contacts. The GaN layers on sapphire have planar misfit ranging from 1.19 to 16.08%, therefore, epitaxial layers will be grown by domain matching epitaxy where integral multiples of planes match across the film-substrate interface. The misfit strain can be relaxed within two monolayers and the misfit dislocations confined within this layer to reduce the density of threading dislocations. Low-resistivity contacts will be created using novel Ga- and Al-doped ZnO with NiO or MoOx interlayer which increases the work function to reduce Schottky barrier. There is a tremendous societal benefit from this project as the solid-state lighting (SSL) offers an entirely new lighting paradigm, compared to existing incandescent lighting. The SSL efficiency can approach 400 lm/W, compared to ~ 17 lm/W for incandescent bulb and ~ 50 lm/W for fluorescent bulb with power consumption in SSL an order of magnitude lower than incandescent lighting and life expectancy of over forty years. The proposed research has a strong educational component in terms of teaching and training of graduate students.