Orientation patterned (OP)-GaAs crystals show promise for use in tunable coherent light sources in the infrared (IR) and terahertz (THz). These structures consist of an alternating array of /[00-1] oriented domains grown by hydride vapor phase epitaxy (HVPE). Material characteristics concerning the propagation losses, the crystal dimensions, and the grating size must be taken into account to implement optical devices for specific wavelength ranges and operating modes (CW or pulsed). The analysis of the main factors contributing to optical loss in the OP crystals is a crucial step toward their use in many promising applications. We present a cathodoluminescence study, where the main defects and their distribution over the OP-GaAs crystals are revealed, with special emphasis paid to the properties of the domain walls.