Schematic illustration of GaN wurtzite crystal structure exhibiting the polarity along the c-axis. The small and large spheres indicate Ga and N, respectively. GaN with Ga-face (+c) polarity on left side and GaN with N-face (-c) polarity on right side. When the direction of the three bonds of the III-element is towards the substrate, the polar structure is defended as +c polarity. On the other hand, when that of the bonds is upward against substrate, it is defined as having -c polarity. The termination element on the surface is not specified unless it is explicitly mentioned in this article.
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