Observation and Study of Dislocation Etch Pits in Molecular Beam Epitaxy Grown Gallium Nitride With the Use of Phosphoric Acid and Molten Potassium Hydroxide

Report No. ARL-TR-4164
Authors: Fred Semendy and Unchul Lee
Date/Pages: June 2007; 20 pages
Abstract: Defects continue to challenge the functionality and reliability gallium nitride (GaN)-based devices. GaN grown on sapphire by molecular beam epitaxy was investigated by wet etching in hot phosphoric acid (H3PO4) and molten potassium hydroxide (KOH). Hexagonally shaped etch pits were formed on the etched sample surfaces. Etched samples were characterized with the use of atomic force microscopy (AFM) and scanning electron microscopy (SEM) and SEM cathode luminescence (SEM-CL). AFM images show dark spots indicating mixed dislocations. The densities of the mixed dislocations are almost ~3 x 108 cm2. Observations were made about the three different types of etch pits distinguished as ¿, ¿, and ¿. By comparing SEM and AFM, we made observations about a relationship between etch pits and dislocations. The origin of etch pits is the mixed dislocation, and the combination of KOH etching and AFM is found to be a better approach for a two- dimensional evaluation of mixed dislocations. Results showed that both H3PO4 and molten KOH are good wet etchants for GaN and the pits created by H3PO4 were smaller and numerous when compared to the pits created by molten KOH.
Distribution: Approved for public release
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Last Update / Reviewed: June 1, 2007