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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.

Quasi-phase-matched GaAs layers up to 600 μm thick have been produced by low-pressure hydride vapor phase epitaxy (HVPE) regrowth on templates fabricated using wafer fusion bonding. We have used this combination of techniques to demonstrate an alternative approach for commercial development of orientation-patterned GaAs (OP-GaAs) for nonlinear optical frequency conversion applications. We report on the characterization of this material and present a comparison with OP-GaAs grown using the conventional all-epitaxial templates. The primary advantages of the wafer fusion method are the avoidance of the molecular beam epitaxy growth of GaAs/Ge/GaAs and the ability to use substrates without misorientation. We have observed that some of the misorientation-related growth defects which affect conventional OP-GaAs growth are not as problematic for regrowth on wafer fusion bonded templates. The overall quality of antiphase domain propagation was similar to conventional OP-GaAs layers. A disadvantage was that growth rates were approximately half the values measured for regrowth on misoriented templates.

This paper describes advances in the development of quasi-phase-matched (QPM) gallium phosphide (GaP) crystals for agile laser sources in the mid-infrared regions between 3–5 and 8–12 μm. In the quest for a nonlinear optical material with the potential to efficiently convert near infrared energy (wavelength ∼1 μm) to a powerful mid-infrared source, we have investigated the growth of GaP by hydride vapor phase epitaxy (HVPE). The process is shown to produce high quality thick layers at rapid growth rates in a low-pressure horizontal reactor. This process was used to grow thick layers on orientation-patterned (OP) templates. The OP-GaP templates were fabricated by lithographic patterning of inverted wafer-fused GaP. HVPE growth on both OP-GaP and OP-GaAs templates was performed, showing that HVPE can successfully replicate the initial template pattern. However, for longer growth duration at given conditions the patterned structure can be lost, with annihilation of every other domain.

The development and scaling-up of a process for the growth of large diameter aluminum nitride thick films on 2-in sapphire is described. Optimal growth rates between 10 and 15 μ m/h have been reached by adjustment of the reactor pressure, substrate temperature and gas flows. The layer thickness is determined by in situ laser reflection from the layer surface and ex situ by the curve of reflectivity versus wavelength after growth. The crystal quality is demonstrated by in situ laser reflection, scanning electron microscopy (cross sectional images and thickness) and atomic force microscopy (average roughness before and after polishing in the ranges of 20–50 and 3–8 nm, respectively).

Halide vapor phase epitaxial growth of GaP was performed on GaP half- and orientation — patterned templates. This allowed optimization of substrate material, patterning approach and pattern orientation, which resulted in growth of +350 μm thick quasi-phase matched GaP with successful replication of the initial patterns.

This article describes efforts to achieve fast deposition of thick Quasi-Phase-Matched (QPM) GaP structures with high surface and structural quality on oriented patterned (OP) templates in a Hydride Vapor Phase Epitaxial (HVPE) process. These QPM structures will be incorporated in devices for conversion of frequencies from the near infrared to the mid infrared and THz regions, where powerful and tunable sources are in great demand for both military and civilian applications. In contrast with GaAs—the most studied OP QPM material—the two-photon absorption of GaP is predicted to be extremely low, which allows pumping with a number of convenient sources between 1 – 1.7 µm. Unpatterned GaP layers up to 370 µm thick were grown with growth rates up to 93 µm/hr with high reproducibility on bare substrates. The layers demonstrated smooth surface morphology with RMS < 1 nm and high structural quality with FWHM equal to 39 arcsec for layers grown on GaP and 112 arcsec for those grown on GaAs. Growth on OP-GaP templates resulted in 142 µm thick QPM structures deposited at a growth rate of 71 µm/h with good vertical (normal to the layer surface) propagation of the initial pattern. When the growth was performed on OP-GaAs one of the domains showed a trend toward a faceting growth. Further investigations are in progress to equalize the vertical and lateral growth of the two domains, and determine the best orientation of the substrate and pattern in order to achieve structures thick enough for high power nonlinear applications.