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Partnership for Solid-State Lighting: Report of a Workshop
A Lack of U.S. Strength in Packaging
In response to a question, a participant addressed the challenge of creating larger wafers and appropriate packaging for more powerful LED systems that give off considerable heat. He said that for larger systems, fabrication technologies could be borrowed from silicon or other wafer-processing technologies. He noted that packaging would be a challenge, because thermal management in high-volume, low-cost packaging is not a forte of industry in this country. For optoelectronics, most of the leaders in LED packaging are now found in Southeast Asia and Japan.
Working Toward Higher Efficiency
Roland Haitz gave two suggestions for the most urgent research objectives of precompetitive research. He said that the efficiency in LED-based lamps was likely to be based on a color-mixing system, where a significant problem is to achieve very good color mixing without excessive loss of light. This goal would involve a search through holographic approaches and “whatever else the physics and optical folks can dream up,” and is appropriate for precompetitive research. A second area would make use of Vertical Cavity Surface Emitting Lasers (VCSELS). For this new laser structure, Sandia National Laboratories have recently demonstrated efficiencies above 50 percent at an infrared wavelength of 980 nm. If these results could be extended over the visible spectrum, a VCSEL-based solution would be preferable to the LED-based solution because the photons are easier to direct. Light distribution and extraction efficiency would be substantially more efficient. However, no one yet has demonstrated a VCSEL beyond about 620 nm in the red, which poses a large and interesting challenge for basic researchers.