This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Controlling dopant concentration near the silicon surface is increasingly important for ultrashallow junctions and nanoscale devices. Mixed monolayer doping (MMLD) offers a surface-chemistry-based approach in which dopant-containing molecules are mixed with nondopant molecules to tune the amount of dopant available at the silicon surface before thermal diffusion.
In a new study, researchers from Ecole Polytechnique Federale de Lausanne doped silicon using mixed monolayers of the phosphorus-containing molecule allyldiphenylphosphine (ADP) and 1-undecene. The team investigated the use of O₂ plasma ashing after molecular grafting to remove residual carbon while preserving phosphorus at the surface. X-ray photoelectron spectroscopy (XPS) confirmed that the plasma treatment reduced carbon content while largely retaining phosphorus.
Kelvin probe force microscopy (KPFM) revealed a systematic decrease in silicon work function with increasing ADP concentration. The results, published in the journal Small Methods, also showed that the SiO₂ capping method strongly influenced the measured surface response: evaporated SiO₂ combined with O₂ plasma treatment produced the clearest evolution toward n-type behavior, whereas sputtered SiO₂ resulted in strong work-function pinning. Electrical characterization using four-point probe and Hall-effect measurements confirmed increasing conductivity and carrier concentration with increasing ADP content.
However, no significant difference was observed between plasma-treated and untreated samples in these bulk-integrated measurements. This highlights the importance of distinguishing between near-surface electronic properties and bulk electrical transport when evaluating monolayer-doped silicon. Overall, the work demonstrates plasma-assisted MMLD with small molecules as a promising, tunable approach to silicon doping while emphasizing the importance of combining surface-sensitive and electrical characterization techniques.
Such control of near-surface doping is particularly relevant for nanoscale and emerging quantum-device applications. Pol Torres‐Vila et al, Impact of Plasma Ashing on Mixed Monolayer Doping of Silicon, Small Methods (2026). DOI: 10.1002/smtd.70970 Provided by Ecole Polytechnique Federale de Lausanne BA art history, MA material culture.
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