Intrinsic ultrasmall nanoscale silicon turns n-/p-type with SiO2/Si3N4-coating

We show in theory and experiment that usn-Si can experience a considerable energy offset of electronic states by embedding it in silicon dioxide or silicon nitride, whereby a few monolayers of SiO2 or Si3N4 are enough to achieve these offsets

Dirk König; Daniel Hiller; Noël Wilck; Birger Berghoff; Merlin Müller; Sangeeta Thakur; Giovanni Di Santo; Luca Petaccia; Joachim Mayer; Sean Smith; Joachim Knoch

2018

Scholarcy highlights

  • Modulation doping – i.e., doping of materials adjacent to semiconductors which provide free carriers to the unperturbed semiconductor – was first used for group III–V semiconductor combinations such as GaAs/AlAs in the late 1970s
  • We prove by hybrid-density functional theory simulations and synchrotron-based long-term ultraviolet photoelectron spectroscopy that usn-Si can have a massive ΔE of their electronic density of states when embedded in SiO2 or Si3N4
  • The section contains experimental results, namely the thickness determination of embedded Si nanowells by transmission electron microscopy and the measurement of the highest occupied DOS over energy for Si-NWell samples embedded in SiO2 or Si3N4 by synchrotron-based long-term UPS. With this experimental confirmation of our h-DFT results, we present the concept of undoped Si-NWire field-effect transistors
  • The frontier-OMOs exist within the Si3N4-embedded Si-NC, while the frontier-UMO exists within the SiO2-embedded Si-NC, with ΔE of the occupied frontier MOs of 0.5 eV and of 1 eV for the unoccupied frontier MOs between both NCs
  • We demonstrated that devices with Si3N4-coating exhibit substantially better on-state performance and strongly reduced dependence on the length of the source/drain regions, showing that high performance small-scale MISFETs can be realized using undoped ultrathin Si-NWires with a combined SiO2-/Si3N4-coating
  • Supporting Information features the comparison of h-DFT results to experimental data, further information on the interface impact on Si nanocrystal electronic structure and its connection to quantum-chemical nature of N and O, details of UPS scans with further reference data, the derivation of charge carrier densities for nonequilibrium Green’s function transport simulation of undoped Si-nanowire MISFET devices and details on NEGF device simulations
  • Doping-related technological obstacles typical in CMOS technology are bypassed altogether, extending the potential of structural miniaturization down to the Si-crystallization limit of ca. 1.5 nm

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