{HEAD ~ The first and second electrodes} are separately disposed on the epitaxial layer structure, and {TAIL ~ the epitaxial layer structure} has a RMS roughness less than 3 nm on a surface wherein the second electrode is formed 
{ HEAD ~ The first and second electrodes } are separately disposed on the epitaxial layer structure , and { TAIL ~ the epitaxial layer structure } has a RMS roughness less than 3 nm on a surface wherein the second electrode is formed
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