Large Area Semipolar GaN Grown on Foreign Substrates

By nucleation of GaN stripes on the c-plane-like side facets of trench-patterned sapphire wafers and their subsequent coalescence, we have realized various semipolar planar GaN layers by metalorganic vapor phase epitaxy. A variation of the miscut of r-plane sapphire wafers did not lead to improved (11-22) GaN layers despite the slight off-orientation between the GaN (11-22) plane and the sapphire r-plane. For (20-21) GaN grown on s-plane sapphire, we only obtained nicely coalesced layers after overgrowth by hydride vapor phase epitaxy (HVPE). However, increased parasitic oxygen incorporation was observed in HVPE growth of such semipolar layers. On the other hand, the Mg incorporation was reduced by about a factor of 8 on (11-22) planes as compared to the polar c-plane.