Abstract
Most blue light LED chips are made by growing GaN epitaxy on a sapphire substrate. Because sapphire is an insulator, the two electrodes on a conventional LED die must lie on the same side. To improve upon existing technology, several companies are developing vertical stacked LED designs by coating P-type GaN with a reflector (e.g. Ag) that is soldered (e.g. via Au-Sn) to an electrode as the substrate. These techniques have their limitations. In this report, we introduce a methodology to producing a high-powered LED with a thin-film DLC (diamond like carbon) interface that can effectively bridge the semiconductor GaN and metallic substrate. DLC can not only moderate the thermal mismatch, but also to enhance the heat spreading since DLC has a thermal conductivity (475 W/mC) that is significantly higher than even copper. In addition, the metal substrate of the LED can optionally be replaced by a diamond-metal (Ni or Cu) composite that further minimizes the CTE mismatch and boost heat spreading efficacy. Such a DLC LED design can sustain a high drive current so that reduced number of enhanced dies can be used in place of conventional chips for small form-factor general illumination applications.
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