Energy filtering and modulation doping are two well-established techniques that have been used independently to enhance the thermoelectric power factor of materials, albeit with moderate success. Energy filtering introduces potential barriers or selective scattering that filter out lower-energy, ‘cold’ carriers to improve the Seebeck coefficient. Modulation doping allows high carrier densities without the mobility degradation typically caused by dopant species, which enhances the electronic conductivity. In this work, using advanced Monte Carlo simulations, coupled self-consistently with electrostatics, we compute the thermoelectric transport in materials containing periodically placed cavity regions filled with dopant species. The latter enables modulation doping effects, but additionally, careful design of these geometries can shape the band profile in a way that facilitates energy filtering. This synergistic effect enables ultra-high thermoelectric power factors, achieving values more than five times greater than the optimal maximum value of the corresponding uniformly doped material. The proposed structures can be fabricated using standard methods, offering new directions in energy-efficient thermoelectric harvesting and cooling applications.