Size‐Dependent Structures and Optical Absorption of Boron‐Hyperdoped Silicon Nanocrystals

Abstract

and intermediate-band transition for bulk Si. [ 19,20 ] For Si NCs, hyperdoping is also emerging as an effective means to obtain novel properties. [21][22][23][24][25][26] For instance, localized surface plasmon resonance (LSPR) may occur to hyperdoped Si NCs. [21][22][23] And the energy of the LSPR can be conveniently tuned by the doping level.It is well known that the properties of intrinsic Si NCs are critically dependent on the NC size. [ 27,28 ] However, the size effect for hyperdoped Si NCs has been hardly explored. Previous work simply focused on the effect of the doping level. It has been recently predicted that the LSPR of hyperdoped Si NCs can be controlled by not only the doping level but also the NC size. [ 29 ] This highlights that the critical role played by the size effect may remain for Si NCs after hyperdoping. Therefore, it is of great interest to also investigate the size effect for hyperdoped Si NCs. Knowledge concerning the effect of the NC size on the dependence of the properties of hyperdoped Si NCs on the doping level should be invaluable for the synthesis of hyperdoped Si NCs with desired functionality.In this work, Si NCs hyperdoped with different B-doping levels are considered. The dependence of the physical properties of hyperdoped Si NCs on the NC size is examined. It is shown that the largest Si NCs undergo a stronger reduction of the average lattice spacing upon doping with respect to the smallest ones. While Raman, subbandgap optical absorption and the LSPR spectra are all modifi ed with increasing B concentrations in Si NCs, they also indicate that the largest Si NCs are less affected by disorder and charge carrier surface scattering. As a result, there exists a range of doping concentrations where the LSPR energy can be blueshifted as the NC size decreases. Results and DiscussionBoth B-hyperdoped and undoped Si NCs with different sizes have been synthesized by using SiH 4 -based nonthermal plasma. [ 6,[30][31][32] The atomic concentrations of B in B-hyperdoped Si NCs are ≈17%, 36%, and 60%, which are measured with inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Transmission electron microscopy (TEM) and Raman

Origin of the Photoluminescence Quantum Yields Enhanced by Alkane-Termination of Freestanding Silicon Nanocrystals: Temperature-Dependence of Optical Properties

“…HR-TEM observation provides direct evidence of the shortened Si-Si bond lengths in 2.4-nm ncSi65. The bond length between atoms decreases with size reduction65. As suggested in those studies, the surface reconstruction might be understood to be caused by a high surface-area-to-volume ratio at the size scale discussed in this work.…”

“…Part of their argument leads us to a possible origin for the nonradiative e-h recombination in the interior of the ncSi:H because of the amorphized layer at the ncSi:H surface. The role of a few-angstrom-thick structurally disordered surface layer on the PL properties of ncGe has also been discussed65. Although further studies are needed, our results obtained from Raman spectroscopic and HAADF-STEM observations suggest that the structurally disordered regions, including the amorphous phase, probably work as one of the nonradiative channels.…”

“…One of the theoretical studies suggests that under-coordinated surface atoms form a shorter Si-Si bond than that of bulk Si60. HR-TEM observation provides direct evidence of the shortened Si-Si bond lengths in 2.4-nm ncSi65. The bond length between atoms decreases with size reduction65.…”

Two‐dimensional heterostructure promoted infrared photodetection devices

“…Apart from the extraordinary performance due to the LSPR effect, the authors also broadened the wavelength region by heavy B doping. The heavy B doping introduced band‐tail states to the Si QDs, giving rise to a sub‐bandgap transition . This is an efficient way to choose a sensitive absorption region, the processing is not straightforward which can be improved by combining the ultranarrow bandgap sensitizer such as Ti 2 O 3 .…”

Density functional theory study on the B doping and B/P codoping of Si nanocrystals embedded in SiO2

“…For example, low-energy light emission related to the transitions of electrons from the band edge to the defect state has been observed in boron (B)-and phosphorus (P)-doped Si NCs [20][21][22][23], leading to enhanced tunability of the light emission from Si NCs. In addition, heavy B and P doping have enabled localized surface plasmon resonance (LSPR) for Si NCs [24][25][26][27][28]. A series of novel devices that take advantage of the dopinginduced properties of Si NCs are now highly expected.…”