LED Lighting for the 21st Century

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A major factor preventing the acceptance of LED lighting in our homes and offices is cost. The Cambridge part of this proposal focuses on reducing the cost by growing LED structures on silicon substrates which are much deeper than the sapphire substrates normally used. Our industrial partner, PhotonStar LED, plans to use ultra-thin flip-chip LEDs, which means that the substrate has to be removed. A major challenge is for Cambridge to incorporate a novel interlayer in the growth process which facilitates the removal of the substrate.Initially Cambridge will use sapphire substrates to test our ideas for interlayers. For example, it is proposed to grow n-GaN on sapphire, followed by an AlGaN interlayer, followed by further growth of n-GaN, and then multi-quantum-wells of InGaN/GaN. The plan is for the AlGaN interlayer to facilitate the removal of the sapphire substrate plus some of the n-GaN.Having developed a suitable interlayer for growth on sapphire we will then move to growth on silicon with an interlayer. Possible candidates are AlN or SiN. Because of the higher dislocation densities in growth on silicon we will need to introduce additional interlayers of other materials to reduce the dislocation density. We will then deliver to PhotonStar LED an ultra-thin, low-cost, GaN LED structure emitting at 450 nm.