Provided herein are PIN structures including a layer of amorphous n-type silicon, a layer of intrinsic GaAs disposed over the layer of amorphous n-type silicon, and a layer of amorphous p-type silicon disposed over the layer of intrinsic GaAs. The layer of intrinsic GaAs may be engineered by the disclosed methods to exhibit a variety of structural properties that enhance light absorption and charge carrier mobility, including oriented polycrystalline intrinsic GaAs, embedded particles of intrinsic GaAs, and textured surfaces. Also provided are devices incorporating the PIN structures, including photovoltaic devices.