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Jan 29th, 2011
Voids cut defects 2–3 orders of magnitude in GaN-on-sapphire
Researchers from North Carolina State University have developed a new technique that reduces defects in gallium nitride (GaN) epitaxial films grown on sapphire substrates, enabling the creation of more efficient light-emitting diodes (‘Embedded voids approach for low defect density in epitaxial GaN films’, Appl. Phys. Lett. 98, 023115 (2011), 17 January).
Normally, dislocations generated at the GaN/sapphire interface run through the crystalline structure of the GaN films until they reach the surface. The researchers started with a GaN film that was 2 microns thick and embedded half of that thickness with large voids that were 1–2 microns long and 0.25 microns in diameter near the sapphire substrate (where high densities of dislocations are present). Generating a high-density network of embedded microvoids (~108/cm2) in the film effectively created a ‘surface’ in the middle of the material, preventing the defects from traveling through the rest of the film. It was found that the defects were drawn to the voids (which act as dislocation sinks or termination sites for the dislocations, which therefore became trapped), leaving the portions of the film above the voids with far fewer defects.
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