Optical absorbance of doped Si quantum dots calculated by time-dependent density functional theory with partial electronic self-interaction corrections

Abstract

The optical properties of Si quantum dots (QDs) with phosphorous and aluminum dopants have been calculated with the recently tested Heyd-Scuseria-Ernzerhof (HSE) density functionals to ascertain the effect of functional corrections to electronic self-interaction. New results have been obtained for 20 crystalline and amorphous structures of Si(29) and Si(35) quantum dots and are compared to our previous results obtained using the PW91∕PW91 functionals. The bandgaps are greater in magnitude and shifted to higher energies in HSE calculations compared to PW91 calculations, and the absorption spectrum is blueshifted in HSE. Trends in the shifts of absorbances due to doping are similar for both sets of calculations, with doped QDs absorbing at lower photon energies than undoped QDs. Consistent with previous results, the bandgaps of QDs are found to decrease as the size of the QD increases, and the absorption spectra of amorphous QDs are redshifted compared to those of crystalline structures. The molecular orbitals involved in the transitions with the largest oscillator strengths show that the electron density moves towards the surface of the quantum dot as the structure is excited. The lifetimes of photoexcited states were found to differ substantially between the two functionals due to their sensitivity to the overlaps of initial and final orbitals. Comparison with available experimental and independent theoretical results supports the conclusion that the HSE functional better matches experimental results due to the partial inclusion of Hartree-Fock exchange.

Theoretical study on the structures and optical absorption of Si172nanoclusters

“…1 However, bulk Si exhibits an indirect band gap which limits its optical absorption efficiency. [15][16][17][18][19] However, most of these studies are based on the bulk-truncated structures. There have been a large number of investigations on the properties of the doped and undoped Si NCs.…”

“…17 17 Pi et al showed that the Si nanocrystals above 4 nm have localized surface plasma resonance (LSPR) effect when they are doped with more than 10 P atoms. In order to study their electronic and optical properties, the surfaces of Si NCs are generally passivated with hydrogen, halogen and hydroxyl, etc.…”

Si78 double cage structure and special optical properties

“…Such silicon nanoscale materials have been termed nanoclusters (NCs), nanocrystals, nanodots, or quantum dots. [16][17][18][19][20][21] Using first-principles calculations, Wang et al 16 investigated the size dependence of the optical properties of the spherical and cylindrical hydrogenpassivated Si nanoparticles, and their findings revealed that the band gap increases and the associated absorption spectrum exhibits a blue shift with the decrease in the diameter of the spheres or cylinders. 1 Therefore, the size and shape control of nanomaterials can provide a new way to tune the physical properties of materials.…”

Optical absorption properties of Ge2–44 and P-doped Ge nanoparticles

“…The maximum displacement was set as 1.8×10 -3 Å. Then, the optical properties were calculated by time-dependent density-functional theory (TDDFT) [48] at B3LYP/6-31G implemented in Gaussian 09 software package [49].…”

“…Experiment [11] shows that amorphous Si nanoparticles have stronger optical absorption than those with higher crystallinity, especially in short wavelength region. Theoretical calculations also show that the absorption spectra of non-crystalline silicon nanoclusters exhibit a red-shift compared to those of crystalline silicon structures, and doping P and Al can cause the spectrum to shift even further toward the red region [12,13]. Furthermore, localized surface plasma resonance (LSPR) can be produced when more than 10 P atoms are doped in a Si nanocrystal of 1.8 -4 nm [14].…”