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

Abstract

Impurity doping of ultrasmall nanoscale (usn) silicon (Si) currently used in ultralarge scale integration (ULSI) faces serious miniaturization challenges below the 14 nm technology node such as dopant out-diffusion and inactivation by clustering in Si-based field-effect transistors (FETs). Moreover, self-purification and massively increased ionization energy cause doping to fail for Si nano-crystals (NCs) showing quantum confinement. To introduce electron- (n-) or hole- (p-) type conductivity, usn-Si may not require doping, but an energy shift of electronic states with respect to the vacuum energy between different regions of usn-Si. We show in theory and experiment that usn-Si can experience a considerable energy offset of electronic states by embedding it in silicon dioxide (SiO2) or silicon nitride (Si3N4), whereby a few monolayers (MLs) of SiO2 or Si3N4 are enough to achieve these offsets. Our findings present an alternative to conventional impurity doping for ULSI, provide new opportunities for ultralow power electronics and open a whole new vista on the introduction of p- and n-type conductivity into usn-Si.

Bridge‐ and Double‐Bonded O and NH on Fully OH‐ and NH2‐Terminated Silicon Nanocrystals: Ground and Excited State Properties

“…This finding originates from the peculiar nature of N which is the only anionic element with a positive electron affinity X e . As a consequence, electronic charge from the Si‐NC gets attracted by an interface charge transfer (ICT) to N but is not much localized there when compared to the situation of O . Thus, frontier occupied molecular orbitals (OMOs) associated with N are more delocalized.…”

“…Figure a. This finding was confirmed in theory and experiment . Due to hybridization, the frontier unoccupied MOs (UMOs) follow suit.…”

“…In experiment, this robustness may contribute to the high energy selectivity of Si‐quantum dot array contacts for hot holes as found in the steady‐state regime of hot carrier solar cells by optically assisted current–voltage (oa‐IV) measurements . For anionic interface terminations (N, O, F), this statement is supported in theory and experiment by the HOMO and LUMO energies being dominated by the type of interface termination, depending only to some degree on NC size. From this finding, we can derive that modified anion groups at Si‐NC interfaces will keep their impact provided the ratio of nominal to modified interface terminations stays constant.…”

“…The smallest Si lattice construct still behaving as NC is the Si 10 cage with 7 Å size . Its full OH‐termination and embedding into up to 3 ML of SiO 2 showed only marginal shifts of HOMO and LUMO energies with a minor increase in the HOMO‐LUMO gap, all clearly correlating with increasing Si 10 ionization . While we acknowledge that strain may influence the electronic properties of Si‐NCs, ionic interface terminations such as O, N, or F with associated strong ICT from the Si‐NC arguably marginalize the impact of strain.…”

“…The termination of Si‐NCs with OH and NH 2 groups have been shown to accurately emulate SiO 2 ‐ and Si 3 N 4 ‐embedding . Although the intial charge distribution within NC approximants is an important parameter for optical excitations, it was only briefly discussed in one publication .…”