Structural characterization of GaN laterally overgrown on a (111)Si substrate

Using transmission electron microscopy, we have characterized defect structures in laterally overgrown GaN crystals, grown directly on SiO_2 stripe-patterned (111)Si substrates by metalorganic vapor phase epitaxy using AlGaN as an intermediate layer. The width and the period of the stripe windows were nominally 1 and 2 μm, respectively. The average threading dislocation density for a completely coalesced 2-μm-thick GaN crystal obtained on the [112]-oriented stripe-patterned substrate was ～ 2*10^9 cm^{-2}. The reduction in threading dislocation density is a consequence of the lateral growth and dislocation reactions at the coalesced front of the mask. On the other hand, valleys and pits tend to remain on the mask during the growth on the [110]-oriented stripe-patterned substrate. Cracks were present in both crystals.