Controlled Doping of Silicon Nanocrystals Investigated by Solution-Processed Field Effect Transistors

Gresback, Ryan; Kramer, Nicolaas J.; Ding, Yi; Chen, Ting; Kortshagen, Uwe R.; Nozaki, Tomohiro

doi:10.1021/nn500182b

Cited by 83 publications

(97 citation statements)

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“…[ 39,40 ] It is known that plenty of B atoms are not activated in Si NCs. [ 21,41 ] The unactivated B atoms may not occupy lattice sites, leading to the structural disorder in Si NCs. The structural disorder may also contribute to the broadening of the Raman peak for Si-Si bonds toward the lower wavenumbers.…”

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confidence: 99%

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

Zhou

et al. 2016

Advanced Optical Materials

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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

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Section: Full Paper Full Paper Full Papermentioning

confidence: 99%

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

Zhou

et al. 2016

Advanced Optical Materials

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“…Si nanostructures are extremely appealing for applications in several fields like microelectronics, optoelectronics, photovoltaics, plasmonics and thermoelectrics. [1][2][3][4] Their exploitation requires controlling the properties of these low dimensional materials by properly tuning the dopant concentration like in bulk semiconductors. 1,[5][6][7] However, a clear understanding of dopant incorporation and subsequent activation at the nanoscale has not yet been achieved.…”

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confidence: 99%

Thermodynamic stability of high phosphorus concentration in silicon nanostructures

Perego¹,

Seguini²,

Arduca

et al. 2015

Nanoscale

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Doping of Si nanocrystals (NCs) has been the subject of a strong experimental and theoretical debate for more than a decade. A major difficulty in the understanding of dopant incorporation at the nanoscale is related to the fact that theoretical calculations usually refer to thermodynamic equilibrium conditions, whereas, from the experimental point of view, impurity incorporation is commonly performed during NC formation. This latter circumstance makes impossible to experimentally decouple equilibrium properties from kinetic effects. In this report, we approach the problem by introducing the dopants into the Si NCs, from a spatially separated dopant source. We induce a P diffusion flux to interact with the already-formed and stable Si NCs embedded in SiO 2 , maintaining the system very close to the thermodynamic equilibrium. Combining advanced material synthesis, multi-technique experimental quantification and simulations of diffusion profiles with a rate-equation model, we demonstrate that a high P concentration (above the P solid solubility in bulk Si) within Si NCs embedded in a SiO 2 matrix corresponds to an equilibrium property of the system. Trapping within the Si NCs embedded in a SiO 2 matrix is essentially diffusion limited with no additional energy barrier, whereas de-trapping is prevented by a binding energy of 0.9 eV, in excellent agreement with recent theoretical findings that highlighted the impact of different surface terminations (H-or O-terminated NCs) on the stability of the incorporated P atoms.

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“…In the accompanying experiments, we investigate the conduction mechanism in films of phosphorus-doped, ligand-free silicon nanocrystals. At the largest electron concentration achieved in our samples, which is half the predicted nc, we find that the localization length of hopping electrons is close to three times the nanocrystals diameter, indicating that the film approaches the metal-insulator transition.Semiconductor nanocrystals (NCs) have shown great potential in optoelectronics applications such as solar cells [1], light emitting diodes [2], and field-effect transistors [3,4] by virtue of their size-tunable optical and electrical properties [5] and low-cost solution-based processing techniques [6,7]. These applications require conducting NC films and the introduction of extra carriers through doping can enhance the electrical conduction.…”

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Metal–insulator transition in films of doped semiconductor nanocrystals

Chen¹,

Reich²,

Kramer³

et al. 2015

Nature Mater

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To fully deploy the potential of semiconductor nanocrystal films as low-cost electronic materials, a better understanding of the amount of dopants required to make their conductivity metallic is needed. In bulk semiconductors, the critical concentration of electrons at the metal-insulator transition is described by the Mott criterion. Here, we theoretically derive the critical concentration nc for films of heavily doped nanocrystals devoid of ligands at their surface and in direct contact with each other. In the accompanying experiments, we investigate the conduction mechanism in films of phosphorus-doped, ligand-free silicon nanocrystals. At the largest electron concentration achieved in our samples, which is half the predicted nc, we find that the localization length of hopping electrons is close to three times the nanocrystals diameter, indicating that the film approaches the metal-insulator transition.Semiconductor nanocrystals (NCs) have shown great potential in optoelectronics applications such as solar cells [1], light emitting diodes [2], and field-effect transistors [3,4] by virtue of their size-tunable optical and electrical properties [5] and low-cost solution-based processing techniques [6,7]. These applications require conducting NC films and the introduction of extra carriers through doping can enhance the electrical conduction. Several strategies for NC doping have been developed. Remote doping, the use of suitable ligands as donors in the vicinity of NC surface, increased the conductivity of PbSe NC films by 12 orders of magnitude [8]. Electrochemical doping, which tunes the carrier concentration accurately and reversibly, resulted in conducting NC films [9,10]. Lately, stoichiometric control has emerged as a strategy to dope lead chalcogenide NCs [11]. Finally, electronic impurity doping of NCs, originally impeded by synthetic challenges [12], was recently achieved in InAs [13] and CdSe [14] NCs.While many experimental studies have been directed towards increasing the conductivity of NC films, there is still no clear consensus on the fundamental question: what is the condition for the metal-insulator transition (MIT) in NC films [15][16][17]? In a bulk semiconductor, the critical electron concentration n M for the MIT depends on the Bohr radius a B according to the well-known Mott criterion [18] n M a 3 B 0.02, where a B = ε 2 /m * e 2 is the effective Bohr radius (in Gaussian units), ε is the dielectric constant of the semiconductor, and m * is the effective electron mass. It is obvious that a dense film of undoped semiconductor NCs is an insulator, while a film of touching metallic NCs with the same geometry is a conductor. Therefore, the MIT has to occur in semiconductor NC films at some criti-FIG. 1. The origin of the metal-to-insulator transition in semiconductor nanocrystal films. The figure shows the cross section of two nanocrystals in contact through facets with radius ρ. The blue spherical cloud represents an electron wave packet which moves through the contact. Such a compact wave pac...

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Controlled Doping of Silicon Nanocrystals Investigated by Solution-Processed Field Effect Transistors

Cited by 83 publications

References 32 publications

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

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

Thermodynamic stability of high phosphorus concentration in silicon nanostructures

Metal–insulator transition in films of doped semiconductor nanocrystals

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