Nanoscale spatial phase modulation of GaN on a V-grooved Si Substrate-cubic phase GaN on Si(001) for monolithic integration

Nanoscale spatial phase modulation of GaN grown on a 355-nm period array of V-grooves fabricated in a Si(001) substrate is reported. Orientation-dependent selective nucleation of GaN in metal-organic vapor phase epitaxy begins from the opposing Si{111} sidewalls and rapidly fills each V-groove. At the initial stages of growth, the GaN deposited on the sidewalls has hexagonal phase with the c-axis normal to the Si{111}. As the growth continues, the filling of the V-groove over these misaligned hexagonal phase regions results in a transition to a cubic phase with its principal crystal axes parallel to those of the Si substrate. In a cross-sectional view perpendicular to the grooves, the defected hexagonal phase region and the clean cubic phase region above it form a boundary at the inside of each V-groove which is parallel to the Si{111} sidewalls. The GaN surface is almost planarized for only 75-nm deposition and is parallel to the original [001] plane of the Si substrate. The GaN clearly exhibits nanoscale spatial phase modulation with a periodic separation of hexagonal and cubic crystal structures across the groove direction for 600-nm deposition, implying a possibility of cubic phase GaN on an isolated single V-groove fabricated in a Si(001) substrate for monolithic integration. The structural/optical properties and stress measurements of this phase-modulated GaN grown on a nanoscale faceted Si surface are presented.