Donor–Acceptor Pair Recombination in Size-Purified Silicon Quantum Dots

Abstract

Shallow impurity doping is an efficient route to tailor optical and electronic features of semiconductor quantum dots (QDs). However, the effect of doping is often smeared by the size, shape, and composition inhomogeneities. In this paper, we study optical properties of almost monodispersed spherical silicon (Si) QDs that are heavily doped with boron (B) and phosphorus (P). The narrow size distribution achieved by a size-separation process enables us to extract doping-induced phenomena clearly. The degree of doping-induced shrinkage of the optical band gap is obtained in a wide size range. Comparison of the optical band gap with theoretical calculations allow us to estimate the number of active donor−acceptor pairs in a QD. Furthermore, we found that the size and detection energy dependence of the luminescence decay rate is significantly modified below a critical diameter, that is ∼5.5 nm. In the diameter range above 5.5 nm, the luminescence decay rate is distributed in a wide range depending on the detection energy even in size-purified Si QDs. The distribution may arise from that of donor−acceptor distances. On the other hand, in the diameter range below 5.5 nm the detection energy dependence of the decay rate almost disappears. In this size range, which is smaller than twice of the effective Bohr radius of B and P in bulk Si crystal, the donor−acceptor distance is not a crucial factor to determine the recombination rate.

Spectral Dependencies of the Stretched Exponential Dispersion Factor and Photoluminescence Quantum Yield as a Common Feature of Nanocrystalline Si

“…The striking surprise is that even all-inorganic (heavily P-and B-doped) Si NCs with an amorphous P,B-rich shell at the surface [49] reveal the feature of peak 1 above the trend guided by the red line. This observation is very unexpected considering that PL emission is interpreted [57] as the donor-acceptor pair recombination in these codoped Si NCs in contrast to the excitonic recombination in undoped Si NCs. Figure 6b shows the are spectrally shifted to place the peak at spectral positions of either peak 1 (opened circles) or peak 2 (cyan circles).…”

Near infrared bioimaging and biosensing with semiconductor and rare-earth nanoparticles: recent developments in multifunctional nanomaterials

“…106 Emission in the NIR-II can be achieved by increasing the size of the silicon NPs and even longer emission wavelengths can be achieved by doping with impurities. 107 In addition, the lifetime and emission wavelength of these NPs can be increased by annealing at an appropriate temperature, subsequently enabling the use of time-gated imaging to remove autofluorescence of tissues in the NIR. 108 Page 27 of 48 Nanoscale Advances…”

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

“…This tuning has been experimentally observed and is clearly related to the presence of donor-acceptor pair recombination. [113][114][115][116][117] Notably, as a consequence of donor-acceptor pair recombination, evidence of carrier multiplication in codoped Si-NCs has been reported. 114…”