AVS 52nd International Symposium
    Science of Semiconductor White Light Topical Conference Monday Sessions
       Session WL-MoA

Paper WL-MoA9
CdSe Nanocrystal Light Emitting Diodes: Toward Full Spectrum White Light Generation

Monday, October 31, 2005, 4:40 pm, Room 310

Session: Science of Semiconductor White Lighting
Presenter: A.H. Mueller, Los Alamos National Laboratory
Authors: A.H. Mueller, Los Alamos National Laboratory
E.A. Akhadov, Los Alamos National Laboratory
M.A. Petruska, Los Alamos National Laboratory
M. Achermann, Los Alamos National Laboratory
V.I. Klimov, Los Alamos National Laboratory
M.A. Hoffbauer, Los Alamos National Laboratory
Correspondent: Click to Email
Semiconductor nanocrystals (NCs) of CdSe exhibit light emission across the visible light spectrum with optical excitation quantum efficiencies (QE) exceeding 80%. With the emission wavelength determined by the NC size, blends of different size NCs as chromophores can be used to generate a broadband white light spectrum. The ultimate efficiency of such a source will be determined not by the NC’s QE, but by the efficiency of the excitation source. Alternatively, direct electrical excitation of NCs can eliminate inefficiencies in photon absorption and re-emission by the chromophore. Previous electrically pumped NC-LEDs used hybrid polymer/NC architectures to achieve direct injection of carriers into the active layer. Efficiency in these devices is limited by the poor carrier mobilities in the organic components, and they exhibit short operative lifetimes due to photooxidation of the injection layers. These barriers to high efficiencies can be removed by combining inorganic, semiconducting injection layers of GaN with NCs, but this combination is difficult to achieve due to the harsh conditions typically needed for GaN film growth. We have succeeded in fabricating NC LEDs by encapsulating single- and multilayers of CdSe/ZnS core/shell NCs in semiconducting GaN thin films. The GaN films are grown using Energetic Neutral Atom Beam Lithography/Epitaxy (ENABLE), a unique thin film growth technique developed at LANL for growing semiconducting nitride films at low temperatures. Layers of NCs were assembled on a p-GaN substrate using Langmuir-Blodgett (LB) techniques and encapsulated with ENABLE grown n-GaN. This structure allows direct injection of carriers into the NCs, resulting in light emission at a wavelength determined by the NC’s size. Prototype devices have shown emission from single and multicolor NC layers. Ultimately, assemblies of different size NCs as active regions in these LEDs will permit tailoring their output for generating full spectrum white light