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A selectively etched (SE) GaN template for high-power 410-nm InGaN-based LEDs was fabricated, where 2- μm-thick undoped GaN was grown on recess patterned sapphire substrates (PSSs). This was followed by H3PO4 selective etching, 0.5-μm-thick SiO2 film deposition, and a final chemical-mechanical polishing process to remove the excess SiO2. Three kinds of substrates, i.e., conventional sapphire substrates (CSSs), recess PSSs, and SE GaN templates, were used to grow the near-UV LEDs for comparison. The etched pit density of n-type GaN could then be reduced to 105 cm-2, whereas the number of screw-type and edge-type threading dislocations decreased by 16.5% and 49.9%, respectively, since SiO2 fillings on the SE GaN template hindered their propagation. The output power of a near-UV LED fabricated on the SE GaN template was 13% and 46% higher than that of a near-UV LED fabricated on recess PSSs and CSSs, respectively. A substantial improvement in performance can be attributed to the improved epilayer crystallinity and, also, the increased light scattering within the LED induced by SiO2 fillings.
Date of Publication: Nov. 2011