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(a) SEM image of patterned sapphire substrate showing the etched facets on both sides of the striped mesa which are exhibited in different inclined angles. [(b) and (c)] Various magnified top-view SEM images of striped GaN grown on patterned sapphire. Based on the variation of image contrast, the striped GaN can be divided into five different regions. (d) Cross-sectional SEM image taken in tilt-view showing that each GaN stripe consists of two crystallites (as indexed by GaN I and GaN II) with facets in different orientations.
Bright-field (BF) TEM image. (a) Low-magnification image showing the periodicity of GaN crystallites. (b) High-magnification image showing one complete GaN stripe. (c) Two sets of zone axis GaN electron diffraction patterns from GaN I and GaN II with a rotation angle of . (d) Enlarged image of sapphire striped mesa.
dark field images of [(a) and (b)] GaN I, and [(c) and (d)] GaN II taken from and 0002 conditions, respectively. (e) TEM image of GaN grown on the top face of sapphire mesa (region 2) and neighbor region (region 1) during the initial growth stage .
Defect densities in different regions with corresponding terminated facets.
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