For the first time thick orientation-patterned GaP (OPGaP) was repeatedly grown heteroepitaxially on OPGaAs templates as a quasi-phase matched medium for frequency conversion in the mid and longwave IR, and THz regions. The OP templates were fabricated by wafer-bonding and in a MBE-assisted polarity inversion process. Standard low-pressure hydride vapor phase epitaxy (LP-HVPE) was used for one-step growth of up to 400 µm thick device quality OPGaP with excellent domain fidelity. The presented results can be viewed as the missing link between a welldeveloped technique for preparation of OP templates, using one robust nonlinear optical material (GaAs), and the subsequent thick epitaxial growth on them of another material (GaP). The reason for these efforts is that the second material has some indisputable advantages in point of view of thermal and optical properties but the preparation of native templates encounters challenges, which makes it difficult to obtain high quality homoepitaxial growth at an affordable price. Successful heteroepitaxial growth at such a relatively high lattice mismatch (-3.6%) in a close to equilibrium growth process such as HVPE is noteworthy, especially when previously reported attempts, for example, growth of OPZnSe on OPGaAs templates at about 10 times smaller lattice mismatch (+ 0.3%) have produced only limited results. Combining the advantages of the two most promising nonlinear materials, GaAs and GaP, is a solution that will accelerate the development of high power, tunable laser sources for the IR and THz region, which are in great demand on the market.

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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.

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