Conventional impurity doping of nanostructured Si-based transistor structures is subject to several obstacles, in particular: (i) deteriorated charge carrier mobility due to ionized impurity scattering causing both slower switching speeds and increased heat dissipation, (ii) random dopant fluctuations (RDF), (iii) nano-size effects impeding high doping efficiencies due to dielectric mismatch, quantum confinement, etc. Moreover, conventional impurity doping is not cryo-compatible because charge carriers freeze out – unless degenerate doping levels beyond Mott's semiconductor-metal transition are considered. Although it is inevitable to control the charge carrier type and density in Si for any device application, it is not mandatory to incorporate dopants into the semiconductor itself. Here, we present a method that allows to relocate acceptor dopants from substitutional sites in the Si or SiGe lattice into an adjacent SiO2 layer. Modulation Acceptor Doping (MAD) uses unoccupied acceptor states generated by specific trivalent acceptor impurities incorporated in SiO2 with energy levels below the Si valence band edge. A direct and permanent ionization of these acceptor states is realized by electron-tunneling from the adjacent Si, which creates holes as majority charge carriers. This p-type doping method provides higher hole mobilities, self-adjusts via Coulomb blockade its ionization density to minimize RDF, is not significantly affected by nano-size effects, and cannot be frozen out by cryogenic temperatures. In this presentation, different modulation acceptor elements, as predicted by density functional theory (DFT) and deposited via ALD ultra-thin films, are compared. In addition, the application of MAD to transistor test devices is demonstrated.