Epitaxial growth of quasi-phase matched GaP for nonlinear applications: Systematic process improvements

This article presents recent results related to development of thick quasi-phase-matched GaP for incorporation in high power sources radiating in the mid-infrared. The focus was on increasing the growth rate and layer thickness of orientation patterned GaP, while ensuring equal vertical deposition rates and rectangular shape of the domain mesas for both opposite crystallographic lattice orientations. Additionally, we present solutions which confine the presence of uncontrollable hillock growth. The experiments were conducted in a hot-wall horizontal quartz reactor using a standard low-pressure hydride vapor phase epitaxial (HVPE) process. GaP was grown on bare, half-patterned (HP) and orientation-patterned (OP) templates fabricated on (100) GaP and (100) misoriented 4° towards (111)B substrates. The domains were oriented either along the [011] or the [011] direction. We compared a sub-lattice inversion MBE assisted process and a wafer fusion bonding technique to create OP templates. When the growth was performed on bare material, the properly chosen growth conditions resulted in reproducible growth of up to 370 μm thick layers with high optical, surface and structural quality, grown at a growth rate of 100 μm/h in one-hour long experiments and 45 μm/h for 8-h long growths. The presence of a core inside the hillocks growing on the layer surface was eliminated. The hillocks were flattened and widened, which allowed often a single hillock to span several domains with alternating opposite crystallographic orientations, when growth was performed on patterned templates. The HP templates were used to determine the optimal substrate and pattern orientations prior to starting growth experiments on OP-templates. As an additional result they revealed that growth could be hillock-free for certain orientations. Growths on OP templates achieved stable growth rates of 50–70 μm/h with domain walls propagating vertically. The growth followed the periodicity of the initial pattern. The maximal thickness achieved to date on OP GaP is about 350 μm.