Impurity doping in silicon (Si) ultra-large-scale integration is one of the key challenges which prevent further device miniaturization. Using ultraviolet photoelectron spectroscopy and X-ray absorption spectroscopy in the total fluorescence yield mode, we show that the lowest unoccupied and highest occupied electronic states of ≤3 nm thick SiO2-coated Si nanowells shift by up to 0.2 eV below the conduction band and ca. 0.7 eV below the valence band edge of bulk silicon, respectively. This nanoscale electronic structure shift induced by anions at surfaces (NESSIAS) provides the means for low-nanoscale intrinsic Si (i-Si) to be flooded by electrons from an external (bigger, metallic) reservoir, thereby getting highly electron- (n-) conductive. While our findings deviate from the behavior commonly believed to govern the properties of silicon nanowells, they are further confirmed by the fundamental energy gap as per nanowell thickness when compared against published experimental data. Supporting our findings further with hybrid density functional theory calculations, we show that other group IV semiconductors (diamond, Ge) do respond to the NESSIAS effect in accord with Si. We predict adequate nanowire cross-sections (X-sections) from experimental nanowell data with a recently established crystallographic analysis, paving the way to undoped ultrasmall silicon electronic devices with significantly reduced gate lengths, using complementary metal-oxide-semiconductor-compatible materials.

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.

A hexagonal phase in the ternary Ge-Se-Te system with an approximate composition of GeSe0.75 Te0.25 has been known since the 1960s but its structure has remained unknown. We have succeeded in growing single crystals by chemical transport as a prerequisite to solve and refine the Ge4 Se3 Te structure. It consists of layers that are held together by van der Waals type weak chalcogenide-chalcogenide interactions but also display unexpected Ge-Ge contacts, as confirmed by electron microscopy analysis. The nature of the electronic structure of Ge4 Se3 Te was characterized by chemical bonding analysis, in particular by the newly introduced density of energy (DOE) function. The Ge-Ge bonding interactions serve to hold electrons that would otherwise go into antibonding Ge-Te contacts.

AbstractIm ternären System Ge‐Se‐Te ist seit den 1960er Jahren eine hexagonale Phase mit der annähernden Zusammensetzung GeSe0.75Te0.25 bekannt, aber ihre Struktur blieb ungeklärt. Durch chemischen Transport gelang nun die Zucht von Einkristallen zur Bestimmung der Ge4Se3Te‐Struktur. Diese besteht aus Schichten, die – wie elektronenmikroskopische Analysen erhärten – über van‐der‐Waals‐artige schwache Chalkogen‐Chalkogen‐, aber auch über unerwartete Ge‐Ge‐Wechselwirkungen verbunden sind. Die Art der elektronischen Struktur von Ge4Se3Te wurde durch Analyse der chemischen Bindungen bestimmt, speziell mithilfe der neu eingeführten Energiedichte(DOE)‐Funktion. Die bindenden Ge‐Ge‐Wechselwirkungen dienen der Aufnahme von Elektronen, die ansonsten antibindende Ge‐Te‐Zustände einnähmen.

Unerwartete Ge-Ge-Wechselwirkungen im “zweidimensionalen” Ge4Se3Te fanden R. Dronskowski et al., wie in der Zuschrift auf S. 10338 berichtet wird. Die Schichtverbindung wurde mittels chemischen Transports kristallisiert und erstmals strukturell charakterisiert. Ihre elektronische Struktur und der Ursprung der Ge-Ge-Wechselwirkungen wurden mithilfe chemischer Bindungsanalyse und der neu eingeführten Energiedichte(DOE)-Funktion beleuchtet.

Unexpected Ge–Ge interactions were found in “two-dimensional” Ge4Se3Te as reported by R. Dronskowski et al. in their Communication on page 10204 ff. The layered material was crystallized using chemical vapor deposition and then characterized for the first time. Its electronic structure and the chemical cause of the Ge–Ge interactions were examined by chemical bonding analysis and the newly introduced density of energy (DOE) function.