Embedded microvoids improve LED output

Despite attempts to reduce dislocation densities in gallium nitride (GaN) epitaxial films grown on sapphire structures, dislocation densities on the order of 109 cm-2 still persist.

Despite attempts to reduce dislocation densities in gallium nitride (GaN) epitaxial films grown on sapphire structures, dislocation densities on the order of 109 cm-2 still persist. But a new technique from researchers at North Carolina State University (Raleigh, NC) to physically embed microvoids in epitaxial GaN films very close to the sapphire substrate layer can decrease dislocation densities to the 107 cm-2 range. These defect reductions can improve the light output by a factor of three for GaN-based LEDs.

A 2-to-3-μm-thick GaN film is first grown on a sapphire substrate via metalorganic chemical-vapor deposition (MOCVD). Next, GaN nanowires are created by etching this layer. Then, another layer of GaN is grown on top of the nanowires, trapping bubbles of air that create oval and vertically oriented microvoids a few microns long and less than a micron in diameter. As these voids are created at the nanowire locations near the interface of the sapphire substrate, they act as "sinks" or termination sites for any voids or dislocations that might occur during the growth process, effectively reducing the final number of defects. Contact Salah M. Bedair at[email protected].

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