Pure dopant deposition of B and Ga for ultrashallow junctions in Si-based devices

Envisioning wide future relevance, work is reviewed here on the pure dopant deposition of boron (PureB), gallium (PureGa) and the combination of the two (PureGaB), as used in the fabrication of nanometer shallow p⁺n Si and/or Ge diodes. Focus is placed on the special properties that have put these diodes in a class apart: their ideal electrical behavior together with their electrical, optical and chemical robustness have lead to cutting-edge application as photodiodes for detecting low-penetration-depth beams, as for example in EUV lithography and low-energy electron SEM imaging. Of key importance is the effectively high Gummel number of the p⁺-region that provides low saturation currents despite the shallowness of the junctions. Based on experimental evidence it is proposed here that this is related to the formation of a practically complete surface coverage of acceptor states as an interface property of PureB on Si and PureGa on both Si and Ge.