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SEM micrographs of GaN on nanoscale patterned pore arrays prepared by two different lithographic techniques. (a) The nanoscale patterned template prepared by the polystyrene nanosphere lithography and interferometric lithography. (b) Nanoislands during the initial regrowth stage (typical thickness of GaN: ). (c) Partial coalescence of GaN regrowth with an increase in the growth time where voids (pits) are seen at the coalescence boundaries of the nanoisland growth fronts (typical thickness of GaN: ). (d) Fully coalesced continuous GaN film after a certain growth duration (typical thickness of GaN: ).
Cross-sectional TEM micrographs of overgrown GaN on nanoscale patterned hole arrays on GaN templates prepared by (a) nanosphere lithography and (b) interferometric lithography techniques. The typical coalescence boundary defects are marked by arrowheads.
(Color online) Room temperature micro-PL and Raman spectra recorded from overgrown GaN grown on the nanoscale hole arrays (dashed lines) and on the nonpatterned regions (solid lines). (a) GaN overgrown on template prepared by nanosphere lithography (I) and GaN overgrown on template prepared by interferometric lithography (II). (b) The phonon blueshift is clearly seen in the patterned regions, which implies a relaxation of tensile stress.
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