Frequency conversion in orientation-patterned (OP) materials is a leading approach for generating mid- and long-wave IR radiation. Although several phase-matching and quasi-phase-matching (QPM) materials have been investigated to date none of these have met all requirements for power, tunability and frequency range of the pursuit applications. We present an original approach that successfully combines in a QPM heterostructure two of the most promising materials, GaP—a material with lower two and three-photon absorption than GaAs, and GaAs—a material with a mature process for fabrication of high quality OP templates. Up to 300 µm thick OPGaP with excellent domain fidelity has been repeatedly grown with 100 µm/h by hydride vapor phase epitaxy on the robust and high quality OPGaAs templates. Some simplifications of both template fabrication and growth process are also reported. The samples, characterized by AFM, SEM, XRD, EDS and TEM, showed smooth surface morphology and high crystalline quality. Special attention was paid to the interface and especially to the mechanism of forming an intermediate ternary transition layer. This led to determining certain criteria that indicate, which other heteroepitaxial cases would be also successful. Thick growths of GaAsP and GaP on other alternative substrate materials by combining a-close-to-equilibrium with a-far-from-equilibrium processes were also performed. Efforts to develop heterostructures in horizontal and vertical direction have been also made. The success with one less favorable (in point of view of lattice mismatch) case, presented here, indicates that we should have even better results in other cases with closer lattice matches.