Development of Key Technologies for White Lighting Based on Light-Emitting Diodes (LEDs)

This program was organized to focus on materials development issues critical to the acceleration of solid-state lighting, and was split into three major thrust areas: (1) study of dislocation density reduction for GaN grown on sapphire using 'cantilever epitaxy', and the impact of dislocation density on the performance of state-of-the-art high-power LEDs; (2) the evaluation of in situ techniques for monitoring gas phase chemistry and the properties of GaN-based layers during metal-organic vapor phase epitaxy (MOCVD), and (3) feasibility for using semiconductor nanoparticles ('quantum dots') for the down-conversion of blue or ultraviolet light to generate white light. The program included a partnership between Lumileds Lighting (epitaxy and device fabrication for high power LEDs) and Sandia National Laboratories (cantilever epitaxy, gas phase chemistry, and quantum dot synthesis). Key findings included: (1) cantilever epitaxy can provide dislocation density reduction comparable to that of more complicated approaches, but all in one epitaxial growth step; however, further improvements are required to realize significant gains in LED performance at high drive currents, (2) in situ tools can provide detailed knowledge about gas phase chemistry, and can be used to monitor and control epitaxial layer composition and temperature to provide improved yields (e.g., a fivefold increase in color targeting is demonstrated for 540nm LEDs), and (3) quantum efficiency for quantum dots is improved and maintained up to 70% in epoxy thin films, but further work is necessary to increase densification (absorption) and robustness before practical application to LEDs

Energy Frontier Research Center for Solid-State Lighting Science: Exploring New Materials Architectures and Light Emission Phenomena

The Energy Frontier Research Center (EFRC) for Solid-State Lighting Science (SSLS) is one of 46 EFRCs initiated in 2009 to conduct basic and use-inspired research relevant to energy technologies. The overarching theme of the SSLS EFRC is the exploration of energy conversion in tailored photonic structures. In this article we review highlights from the research of the SSLS EFRC. Major research themes include: studies of the materials properties and emission characteristics of III-nitride semiconductor nanowires; development of new phosphors and II−VI quantum dots for use as wavelength downconverters; fundamental understanding of competing radiative and nonradiative processes in current-generation, planar light-emitting diode architectures; understanding of the electrical, optical, and structural properties of defects in InGaN materials and heterostructures; exploring ways to enhance spontaneous emission through modification of the environment in which the emission takes place; and investigating routes such as stimulated emission that might outcompete nonradiative processes

Tunnel Contact Junction Aluminum Gallium Arsenide-Gallium Arsenide-Indium Gallium Arsenide Quantum-Well Heterostructure Lasers and Light Emitters With Native-Oxide-Defined Lateral Currents

67 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1999.Data are presented on AlGaAs-GaAs-InGaAs native-oxide-defined quantum well heterostructures utilizing a tunnel contact junction including edge-emitting lasers, vertical cavity surface emitting lasers, and resonant cavity light emitting diodes. These devices display improved electrical characteristics and provide a means to create thin highly defined cavities in semiconductor light-emitting structures.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD

Thermal oxidation of lattice mismatched Al1-xInxN films on GaN

Lattice-mismatched Al1-xInxN layers grown on GaN and with varying x are thermally oxidized to understand how alloy content affects the oxidation process and oxide films. The samples are oxidized in a horizontal tube furnace at 830 oC and 900 oC for 2 h under O2. The samples are characterized using atomic force microscopy to determine root mean square roughness before and after oxidation. The oxide thickness for each sample is determined by spectroscopic ellipsometry. The AlInN layers with less indium produce smoother oxide layers, and the oxidation rate of the samples increases with increasing indium content. Energy dispersive X-ray spectroscopy of scanning transmission electron microscopy images of the oxide layers show the In collects on or near the surface of the oxide layer. Overall, the results indicate that oxides formed from AlInN layers with less indium produce smoother oxide films and are more suitable for device applications

Effect of interface roughness on Auger recombination in semiconductor quantum wells

Auger recombination in a semiconductor is a three-carrier process, wherein the energy from the recombination of an electron and hole pair promotes a third carrier to a higher energy state. In semiconductor quantum wells with increased carrier densities, the Auger recombination becomes an appreciable fraction of the total recombination rate and degrades luminescence efficiency. Gaining insight into the variables that influence Auger recombination in semiconductor quantum wells could lead to further advances in optoelectronic and electronic devices. Here we demonstrate the important role that interface roughness has on Auger recombination within quantum wells. Our computational studies find that as the ratio of interface roughness to quantum well thickness is increased, Auger recombination is significantly enhanced. Specifically, when considering a realistic interface roughness for an InGaN quantum well, the enhancement in Auger recombination rate over a quantum well with perfect heterointerfaces can be approximately four orders of magnitude

Strain compensation in InGaN-based multiple quantum wells using AlGaN interlayers

Data are presented on strain compensation in InGaN-based multiple quantum wells (MQW) using AlGaN interlayers (ILs). The MQWs consist of five periods of InxGa1-xN/AlyGa1-yN/GaN emitting in the green (λ ∼ 535 nm ± 15 nm), and the AlyGa1-yN IL has an Al composition of y = 0.42. The IL is varied from 0 - 2.1 nm, and the relaxation of the MQW with respect to the GaN template layer varies with IL thickness as determined by reciprocal space mapping about the (202¯5) reflection. The minimum in the relaxation occurs at an interlayer thickness of 1 nm, and the MQW is nearly pseudomorphic to GaN. Both thinner and thicker ILs display increased relaxation. Photoluminescence data shows enhanced spectral intensity and narrower full width at half maximum for the MQW with 1 nm thick ILs, which is a product of pseudomorphic layers with lower defect density and non-radiative recombination