Visible-Color-Tunable Light-Emitting Diodes
ABSTRACT Visible-color-tunable light-emitting diodes (LEDs) with electroluminescent color that changes continuously from red to blue by adjusting the external electric bias are fabricated using multifacetted GaN nanorods with anisotropically formed 3D InGaN multiple-quantum wells. Monolithically integrated red, green, and blue LEDs on a single substrate, operating at a fixed drive current, are also demonstrated for inorganic full-color LED display applications.
SourceAvailable from: Mehrdad Djavid[Show abstract] [Hide abstract]
ABSTRACT: We report on the demonstration of a new type of axial nanowire LED heterostructures, with the use of self-organized InGaN/AlGaN dot-in-a-wire core-shell nanowire arrays. The large bandgap AlGaN shell is spontaneously formed on the sidewall of the nanowire during the growth of AlGaN barrier of the quantum dot active region. As such, nonradiative surface recombination, that dominates the carrier dynamics of conventional axial nanowire LED structures, can be largely eliminated, leading to significantly increased carrier lifetime from ~0.3 ns to 4.5 ns. The luminescence emission is also enhanced by orders of magnitude. Moreover, the p-doped AlGaN barrier layers can function as distributed electron blocking layers (EBLs), which is found to be more effective in reducing electron overflow, compared to the conventional AlGaN EBL. The device displays strong white-light emission, with a color rendering index of ~95. An output power of >5 mW is measured for a 1 mm × 1 mm device, which is more than 500 times stronger than the conventional InGaN axial nanowire LEDs without AlGaN distributed EBLs.Scientific Reports 01/2015; 5:7744. DOI:10.1038/srep07744 · 5.08 Impact Factor
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ABSTRACT: We report the growth of GaN micro-rods and coaxial quantum-well heterostructures on graphene films, together with structural and optical characterization, for applications in flexible optical devices. Graphene films were grown on Cu foil by means of chemical vapor deposition, and used as the substrates for the growth of the GaN micro-rods, which were subsequently transferred onto Si02/Si substrates. Highly Si-doped, n-type GaN micro-rods were grown on the graphene films using metalorganic chemical vapor deposition. The growth and vertical alignment of the GaN micro-rods, which is a critical factor for the fabrication of high-performance lightemitting diodes (LEDs), were characterized using electron microscopy and X-ray diffraction. The GaN micro-rods exhibited promising photoluminescence characteristics for optoelectronic device applications, including room-temperature stimulated emission. To fabricate flexible LEDs, InxGai,N/GaN multiple quantum wells and a p-type GaN layer were deposited coaxially on the GaN micro-rods, and transferred onto Ag-coated polymer substrates using lift-off. Ti/Au and Ni/Au metal layers were formed to provide electrical contacts to the n-type and p-type GaN regions, respectively. The micro-rod LEDs exhibited intense emission of visible light, even after transfer onto the flexible polymer substrate, and reliable operation was achieved following numerous cycles of mechanical deformation. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.09/2014; 2(9):092512. DOI:10.1063/1.4894780
01/2014; 9(4):18-22. DOI:10.9790/1676-09411822