Pulsed selective epitaxial growth of hexagonal GaN microprisms

Hexagonal GaN microprism structures were fabricated by pulsed selective epitaxial growth (SEG) under conditions that suppressed lateral overgrowth. Unlike previously reported pulsed SEG processes in which the precursor gas flow was modulated by valves, the approach reported here utilizes a flow geometry that produces a significant deposition rate only over the downstream portion of the 2 in wafer, which yields a pulsed deposition process when combined with substrate rotation. Hexagonal GaN microprism structures were grown on a GaN/sapphire substrate with a dielectric (SiO_x) mask of varying thickness (100, 150, and 200 nm) with circular openings ranging from 4 to 20 μm in diameter. Optimal structures were obtained with a SiO_x mask thickness of 200 nm and circular openings of 6 and 8 μm. The vertical growth rate of the hexagonal prism structures was ∼50 nm/min, corresponding to the deposition of approximately six GaN bilayers (∼1.7 nm) per cycle. This pulsed deposition process has advantages over etching processes for fabricating hexagonal microprisms for optical cavity devices, including elimination of etching damage and formation of crystallographic facets with a high degree of parallelism.