Molecular Modulation of Conductivity on H‐Terminated Silicon‐On‐Insulator Substrates

Abstract The adsorption of a range of molecular species (water, pyridine, and ammonia) is found to reversibly modulate the conductivity of hydrogen‐terminated silicon‐on‐insulator (H‐SOI) substrates. Simultaneous sheet‐resistance and Hall‐effect measurements on moderately doped (10¹⁵ cm⁻³) n‐ and p‐type H‐SOI samples mounted in a vacuum system are used to monitor the effect of gas exposure in the Torr range on the electrical‐transport properties of these substrates. Reversible physisorption of “hole‐trapping” species, such as pyridine (C₅H₅N) and ammonia (NH₃) produces highly conductive minority‐carrier channels (inversion) on p‐type substrates, mimicking the action of a metallic gate in a field‐effect transistor. The adsorption of these same molecules on n‐type SOI induces strong electron‐accumulation layers. Minority/majority channels are also formed upon controlled exposure to water vapor. These observations can be explained by a classical band‐bending model, which considers the adsorbates as the source of a uniform surface charge ranging from +10¹¹ to +10¹²q cm⁻². These results demonstrate the utility of DC transport measurements of SOI platforms for studies of molecular adsorption and charge‐transfer effects at semiconductor surfaces.