Zinc germanium phosphide (ZnGeP2, ZGP) crystal is an excellent mid-infrared nonlinear optical material. In this study, high-pure polycrystalline ZGP was synthesized successfully by using a self-made two-zone tube furnace with the amount of 600 g in one run. A large ZGP single crystal with size of 55 mm×30 mm×160 mm was grown by the horizontal gradient freeze method with ultralow gradient (0.5-1 ℃/cm). The large ZGP crystal devices (12 mm×12 mm×50 mm) with low absorption coefficient of 0.03 cm-1 at 2.09 μm were successfully fabricated after orienting, cutting, post-growth thermal annealing, polishing, and high energy beam irradiation. The crystal devices are used for high energy and high average power infrared laser output.