The energy band alignment of Si nanocrystals in SiO2

Abstract

The determination of the energy band alignment between the 2.6-nm-diameter Si nanocrystals and the SiO2 host is achieved by means of photo-ionization/-neutralization and capacitance spectroscopy. The measured conduction and valence band offsets are 2.6 eV and 4.4 eV. The band gap is evaluated to be 1.7 eV by photoluminescence. These results indicate that the valence band offset at the Si nanocrystals/SiO2 interface is quite close to the one observed at bulk Si/SiO2 interface. On the contrary, we observe a clear upward shift (0.5 eV) of the conduction band in the Si nanocrystals/SiO2 system with respect to the bulk Si/SiO2 hetero-structure.

Nature of intrinsic and extrinsic electron trapping in SiO2

“…For instance, these traps are expected to appear below the conduction band of Si nanocrystals in the case of quantum confinement. 56,57 We suggest that the intrinsic electron traps in a-SiO 2 discussed in this work could be good candidates for understanding these data. The calculated concentration of the electron traps approaches the experimentally observed value for the states filled by direct tunneling from semiconductor substrate or photo-stimulated tunnelling from SiO 2 valence band.…”

Energetics and carrier transport in doped Si/SiO2quantum dots

“…40,59 Therefore, to compensate such deviations, we have applied a correction of 2.0 eV to VBO and HB values, and of -0.8 eV to CBO and EB values, while leaving E g unchanged. Since our QD size range is small, we apply the same correction for all the samples.…”

Novel silicon phases and nanostructures for solar energy conversion

“…To verify the robustness of our results, we repeated some of our electronic structure calculations for two samples: Si 35 123 Zn 188 S 201 samples, respectively; we also obtained an essentially rigid shift of the EDOS of the nanocomposites, both for the valence and the conduction bands. In addition, we found that also at the PBE0 level of theory, the state at the CBM is localized on the nanoparticle and that the VBM is in the host matrix.…”

“…For example, Si NPs embedded in SiO 2 form a type I interface. [122][123][124] Recently, we showed that type-II interfaces may be realized by strain engineering when SiNPs are embedded in amorphous SiO 2 . 47 Using ab initio calculations, we showed that it is possible to design non-stoichiometric nanocomposites that exhibit a type-II hetero-junction at ambient conditions, unlike bulk crystalline Si and ZnS, 125 with complementary charge transport channels for electrons and holes.…”

“…We then replaced all Zn and S atoms within a given spherical region by Si atoms. The center and radius of the sphere were chosen to obtain Si NPs with each surface atom having at most two Si-Zn or Si-S bonds; this resulted in 1.1 nm, 1.3 nm, 1.6 nm, and 1.9 nm NPs, denoted as Si 35 , Si 66 , Si 123 , and Si 172 , respectively. The resulting configurations were used to start annealing cycles to amorphize the ZnS matrix, employing ab initio molecular dynamics (MD).…”