Innovative Development of Next-Generation and Energy-Efficient Solid-State Light Sources for General Illumination
Investigating Organization
Georgia Institute of Technology
Principal Investigator(s)
Mr. Ian Ferguson
Subcontractor
None
Funding Source
EE Science Initiative
Award
DOE Share: $500,000; Contractor Share: $125,000
Contract Period
09/30/03 - 07/31/06
GaN and InGaN, the base materials for light emitting diodes in the blue and UV parts of the spectrum, were grown on ZnO substrates using MOCVD. These materials are currently being characterized via several techniques, including X-ray diffraction, secondary ion mass spectroscopy, and etch pit density in conjunction with atomic force microscopy. Baseline GaN was already measured with respect to defect density, which was 3-5x108 cm-2. In situ substrate removal has not yet been successful. Other alternative substrates (e.g., NdGaO3) will be tested over the coming year, and we expect to obtain defect densities of the materials grown on ZnO shortly. In addition, progress has been made on reducing the 1100°C process temperature through the use of alternative nitrogen sources such as an atomic nitrogen plasma or dimethylhydrazine to replace ammonia. Reduction of the process temperature allows use of many other alternative substrates.
Phosphors were made from SrS and SrGa2S4 activated with Eu. We expect to have similar materials using Ce as the active material over the coming year. The SrS and SrGa2S4 doped with Eu were made into nanoparticles that enhanced their emission efficiency. The emission measured by photoluminescence peaked at 616nm (orange/red).
Light emitting diodes were fabricated using metal-organic chemical vapor deposition of GaN and InGaN multiple quantum wells. These diodes were optimized for emission at 400nm. A second round of diodes has already been fabricated, one year ahead of schedule, with dual wavelength emissions at 418nm and 481nm. These diodes are being incorporated as pump sources with the phosphors mentioned above (SrS:Eu,Ce and SrGa2S4:Eu, Ce as nanoparticles) for measurement of equivalent lumen output. We anticipate measuring the lumen output of the integrated dual wavelength LED driving the phosphors before the new year.