Tunable ballistic rectifiers with different geometries are investigated. On standard structures with a symmetry-breaking scatterer embedded in a cross-bar geometry, we observe—apart from the usual rectification behavior—oscillations in the output characteristics that show the importance of quantum transport for the understanding of the rectification mechanism. On samples that are designed taking semiclassical and quantum transport into account, we find greatly improved rectification efficiency, accompanied, however, by a surprising reversal of the output polarity. We also observe a pronounced step-like increase in the rectified signal. All observations can be explained by a model that takes into account the interplay between classical diffusive, semiclassical, and quantum transport.