Doped and codoped silicon nanocrystals: The role of surfaces and interfaces

Abstract

Si nanocrystals have been extensively studied because of their novel properties and their potential applications in electronic, optoelectronic, photovoltaic, thermoelectric and biological devices. These new properties are achieved through the combination of the quantum confinement of carriers and the strong influence of surface chemistry. As in the case of bulk Si the tuning of the electronic, optical and transport properties is related to the possibility of doping, in a controlled way, the nanocrystals. This is a big challenge since several studies have revealed that doping in Si nanocrystals differs from the one of the bulk. Theory and experiments have underlined that doping and codoping are influenced by a large number of parameters such as size, shape, passivation and chemical environment of the silicon nanocrystals. However, the connection between these parameters and dopant localization as well as the occurrence of self-purification effects are still not clear. In this review we summarize the latest progress in this fascinating research field considering free-standing and matrix-embedded Si nanocrystals both from the theoretical and experimental point of view, with special attention given to the results obtained by ab-initio calculations and to size-, surface- and interface-induced effects

Ab initio studies of the optoelectronic structure of undoped and doped silicon nanocrystals and nanowires: the role of size, passivation, symmetry and phase

“…Therefore, the dependence of the HOMO-LUMO gap on the Si-NC diameter is a direct consequence of the QC effect (the NC shape does not have any inuence) and thus the observed PL is directly related to the states localized inside the Si-NCs. 60,[78][79][80] For the OH-terminated Si-NCs, instead, the changes in the HOMO-LUMO gap are strongly dependent on the oxidation degree (see Table 1) at the NC interface. In fact, in these NCs, the Si atoms at the interface have a different number of nearby O atoms.…”

“…The results obtained revealed that the doped Si nanostructures showed different properties with respect to the doped Si-bulk. [58][59][60] From an experimental point of view, several factors contribute to making the interpretation of the measurements on these systems a difficult task. First of all, independent of the fabrication technique, the degree of reproducibility of a single individual NC is very low.…”

Silicon buckyballs versus prismanes: Influence of spatial confinement on the structural properties and optical spectra of the Si18H12 and Si19H12 clusters

“…It can be said that the effective passivation of silicon clusters (not only by hydrogen atoms) and diluting the silicon framework with the other atoms (e.g., germanium) to change their initial characteristics is an actual modern problem (see Refs. [ ]). In the presented study, we restrict ourselves to hydrogen doped silicon clusters Si 18 H 12 and Si 19 H 12 either pure or endohedral.…”

First Principles Modeling of Si/Ge Nanostructures for Photovoltaic and Optoelectronic Applications

“…During the last years, various efforts have been dedicated to the study of microscopic properties of Si, Ge, and, recently, of Si/Ge NCs and NWs. A large number of works have proven that their structural, electronic, optical, and transport properties are influenced by the occurrence of different concomitant effects that are related to the size, shape, morphology, passivation, presence of defects, doping, and composition . By permitting the isolation and quantification of the effects induced by all these parameters on both ground and excited state properties of low dimensional systems and the simulation of both radiative and non‐radiative recombination mechanisms, numerical simulations have been adopted with success to investigate microscopic properties of complex nanostructured systems .…”