Tuning the Bandgap Character of Quantum‐Confined Si–Sn Alloyed Nanocrystals

Abstract

Nanocrystals in the regime between molecules and bulk give rise to unique electronic properties. Here, a thorough study focusing on quantum-confined nanocrystals (NCs) is provided. At the level of density functional theory an approximate (quasi) band structure which addresses both the molecular and bulk aspects of finite-sized NCs is calculated. In particular, how band-like features emerge with increasing particle diameter is shown. The quasiband structure is used to discuss technological-relevant direct bandgap NCs. It is found that ultrasmall Sn NCs have a direct bandgap in their at-nanoscalestable α-phase and for high enough Sn concentration (≈41%) alloyed Si-Sn NCs transition from indirect to direct bandgap semiconductors. The calculations strongly support recent experiments suggesting a direct bandgap for these systems. For a quantitative comparison many-body GW + Bethe-Salpeter equation (BSE) calculations are performed. The predicted optical gaps are close to the experimental data and the calculated absorbance spectra compare well with the corresponding measurements.

Stimulated emission at 1.54 μm from erbium/oxygen-doped silicon-based light-emitting diodes

“…These ions appear in high density in relatively uniformly sized, Er-related clusters with a diameter of ~1 nm, which is much smaller than the 5 nm diameter achieved with the standard RTA process [11]. Moreover, the spatial distribution of the small clusters is extremely even, which provides very useful conditions for the Er/O cluster to act as a broad and quasi-continuous donor band [42]. The decaying carriers from the Si host into the Er-related states excite the 4f-electron of Er 3+ , which produces the emission at ~1.54 µm.…”

Silicon-Tin Alloyed Nanocrystals by Femtosecond Laser Plasma

“…We could achieve the synthesis of SiSn NCs with Sn concentration of around 17 % and with size around 5 nm. To understand the thermal stability of SiSn-NCs observed experimentally, we calculate the cohesive and the formation energies of Si 0.83 Sn 0.17 NCs by means of First-principle calculations [10]. Our calculations also showed that the alloyed Si 0.83 Sn 0.17 NCs fabricated by fs-laser plasma show an excellent thermal stability up to 400 °C.…”

“…The peak pulse power is calculated to be about 0.84 GW using a measured energy of 70 J, with a pulse of 83 fs at 1 kHz frequency, and a wavelength of 360 nm. To model the nanocrystal geometry, we generate an initial structure with the desired radius cutout from the corresponding bulk lattice (diamond cubic lattice) with undercoordinated surface atoms removed, and fully passivated by hydrogen [10].…”

Quasi-band structure of quantum-confined nanocrystals

“…The degree of quantumconfinement, which can be for example controlled by the particle diameter as well as different functional groups on the NC's surface, allows to tune electronic and optical properties, such as the electronic gap, absorption and luminescence. [6][7][8][9][10][11] Nanocrystals with tailored properties are very attractive for various application requiring distinct optical and electronic properties, such as fluorescent NC for bio-imaging, light absorbing NC for next-generation photovoltaics or luminescent NC for light emitting devices. 9,[12][13][14][15][16][17][18] Essentially, quantum-confined NCs are systems that fall somewhere in between the molecular and the bulk world.…”