Paper EM+SS-ThM6
High-Quality, Large-Area, and Free-Standing GaN Epilayer Growth and Liftoff using Self-Assembled Interlayer of Silica Microspheres

Thursday, October 21, 2010, 9:40 am, Room Dona Ana

We demonstrate that self-assembled monolayers of silica microspheres can be used as inexpensive, selective growth masks for both significant threading dislocation density reduction and laser-free lift-off of GaN epilayers and devices. Silica microspheres self-assemble into close-packed monolayers on the surface of an initial GaN epilayer on sapphire using a Langmuir-Blodgett method. In a subsequent GaN regrowth, the silica microspheres effectively terminate the propagation of threading dislocations. As a result, the threading dislocation density, measured by large area AFM and CL scans, is reduced from 3.3 × 10⁹ cm^-2 to 4.0 ×10⁷ cm^-2. This nearly two orders of magnitude reduction is attributed to a dislocation blocking and bending by the unique interface between GaN and silica microspheres. The sequential wet etching of the samples in HF solution removes the silica microspheres sandwiched between the GaN epilayers and the growth template. Further wet etching of the samples in KOH solution successfully detaches the GaN epilayers from the growth templates. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under contract DE-AC04-94AL85000.