Exchange-Coupled Donor Dimers in Nanocrystal Quantum Dots

Pereira, Rui N.; Almeida, Adelaide; Stegner, Andre R.; Brandt, Martin S.; Wiggers, Hartmut

doi:10.1103/physrevlett.108.126806

Cited by 24 publications

(22 citation statements)

References 31 publications

(50 reference statements)

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“…The exchange interaction influences the energy levels of both P-atoms in a non-trivial way since the exact atomic configuration of the P-dimer determines the exchange energy, as investigated in detail by Pereira et al . 46, 47 . Although this issue is not considered in detail here, we argue that low free carrier densities caused by small amounts of substitutional P-atoms cannot be efficiently overcome by increasing P-concentrations.…”

Section: Discussionmentioning

confidence: 99%

Defect-Induced Luminescence Quenching vs. Charge Carrier Generation of Phosphorus Incorporated in Silicon Nanocrystals as Function of Size

Hiller

López-Vidrier

Gutsch

et al. 2017

Sci Rep

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Phosphorus doping of silicon nanostructures is a non-trivial task due to problems with confinement, self-purification and statistics of small numbers. Although P-atoms incorporated in Si nanostructures influence their optical and electrical properties, the existence of free majority carriers, as required to control electronic properties, is controversial. Here, we correlate structural, optical and electrical results of size-controlled, P-incorporating Si nanocrystals with simulation data to address the role of interstitial and substitutional P-atoms. Whereas atom probe tomography proves that P-incorporation scales with nanocrystal size, luminescence spectra indicate that even nanocrystals with several P-atoms still emit light. Current-voltage measurements demonstrate that majority carriers must be generated by field emission to overcome the P-ionization energies of 110-260 meV. In absence of electrical fields at room temperature, no significant free carrier densities are present, which disproves the concept of luminescence quenching via Auger recombination. Instead, we propose non-radiative recombination via interstitial-P induced states as quenching mechanism. Since only substitutional-P provides occupied states near the Si conduction band, we use the electrically measured carrier density to derive formation energies of ~400 meV for P-atoms on Si nanocrystal lattice sites. Based on these results we conclude that ultrasmall Si nanovolumes cannot be efficiently P-doped.Since the first reports about (heavy) P-doping of silicon nanocrystals (Si NCs), luminescence quenching was often attributed to non-radiative exciton recombination with P-induced free carriers (Auger recombination) 1 . Only few works addressed alternative quenching mechanisms like defects 2-4 . We note that a direct proof of successful P-doping is nontrivial since a true free carrier is not generated due to its confinement in the quantum dot (QD). One important parameter in the investigation of P-doped, oxide-embedded Si NCs is the excess Si concentration that determines the size and separation of NCs as well as the degree of agglomeration. While isolated and mainly spherical NCs are formed at low Si concentrations, excess Si contents above the percolation threshold form highly irregular agglomerated Si NC networks. The threshold that separates these regimes is SiO x≈0.6 for very thin films in a superlattice (SL) and SiO x≲1 for thick bulk films [5][6][7] . While the investigation of P-doping of small and well-separated Si NCs remains a challenging task, it does not come as a surprise that extended Si NC networks can be doped successfully 8,9 . Another important parameter is the dopant concentration and the term doping itself. The latter requires a disambiguation for crystallites at the bottom end of the nanoscale where it is often used deceptively for: (i) the bare incorporation of P-atoms into nanocrystals, (ii) the observation of optical or electrical effects caused by P-incorporation, and (iii) the actual generation of free majority charge carr...

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Section: Discussionmentioning

confidence: 99%

Defect-Induced Luminescence Quenching vs. Charge Carrier Generation of Phosphorus Incorporated in Silicon Nanocrystals as Function of Size

Hiller

López-Vidrier

Gutsch

et al. 2017

Sci Rep

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“…The considerable broadening of dopant profiles from drain/source regions into gate areas persists [3]. Moreover, required ULSI transistor functionality and emerging applications of Si-nanocrystals (NCs) [4] unveiled additional doping issues: self-purification [5–6], suppressed dopant ionization [7–8] and dopant-associated defect states [8–9]. …”

Section: Introductionmentioning

confidence: 99%

Intrinsic ultrasmall nanoscale silicon turns n-/p-type with SiO₂/Si₃N₄-coating

König¹,

Hiller²,

Wilck³

et al. 2018

Beilstein J. Nanotechnol.

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Impurity doping of ultrasmall nanoscale (usn) silicon (Si) currently used in ultralarge scale integration (ULSI) faces serious miniaturization challenges below the 14 nm technology node such as dopant out-diffusion and inactivation by clustering in Si-based field-effect transistors (FETs). Moreover, self-purification and massively increased ionization energy cause doping to fail for Si nano-crystals (NCs) showing quantum confinement. To introduce electron- (n-) or hole- (p-) type conductivity, usn-Si may not require doping, but an energy shift of electronic states with respect to the vacuum energy between different regions of usn-Si. We show in theory and experiment that usn-Si can experience a considerable energy offset of electronic states by embedding it in silicon dioxide (SiO2) or silicon nitride (Si3N4), whereby a few monolayers (MLs) of SiO2 or Si3N4 are enough to achieve these offsets. Our findings present an alternative to conventional impurity doping for ULSI, provide new opportunities for ultralow power electronics and open a whole new vista on the introduction of p- and n-type conductivity into usn-Si.

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“…Owing to the absence of matrix‐induced complication, however, hyperdoped freestanding Si NCs are well positioned for the aforementioned purpose. Up to now, freestanding Si NCs have only been unambiguously hyperdoped with P in nonthermal plasma . In this work, we focus on both B‐ and P‐hyperdoped Si NCs produced in nonthermal plasma with an average size (i.e, ≈14 nm) in the size regime (>12 nm) that is advantageous for the fabrication of electronic devices.…”

Section: Introductionmentioning

confidence: 99%

Boron- and Phosphorus-Hyperdoped Silicon Nanocrystals

Zhou

et al. 2014

Part. Part. Syst. Charact.

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Hyperdoping silicon nanocrystals (Si NCs) to a concentration exceeding the solubility limit of a dopant may enable their novel applications. Here, the successful hyperdoping of Si NCs with boron (B) and phosphorus (P) is demonstrated, which are the most important dopants for Si. Despite the hyperdoping, the diamond structure of Si NCs is hardly modified. There are both electrically active B and P in hyperdoped Si NCs. It is proposed that the hyperdoping is made possible mainly by the kinetics in the nonthermal plasma synthesis of Si NCs. Collision between Si NCs and B or P atoms and the binding energy of B or P at the NC surface are critical to the understanding on the differences in the doping efficiency and dopant distribution between B and P. B‐hyperdoping‐induced tensile stress needs to be taken into account in the investigation on the doping and oxidation of Si NCs.

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Exchange-Coupled Donor Dimers in Nanocrystal Quantum Dots

Cited by 24 publications

References 31 publications

Defect-Induced Luminescence Quenching vs. Charge Carrier Generation of Phosphorus Incorporated in Silicon Nanocrystals as Function of Size

Defect-Induced Luminescence Quenching vs. Charge Carrier Generation of Phosphorus Incorporated in Silicon Nanocrystals as Function of Size

Intrinsic ultrasmall nanoscale silicon turns n-/p-type with SiO₂/Si₃N₄-coating

Boron- and Phosphorus-Hyperdoped Silicon Nanocrystals

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Exchange-Coupled Donor Dimers in Nanocrystal Quantum Dots

Cited by 24 publications

References 31 publications

Defect-Induced Luminescence Quenching vs. Charge Carrier Generation of Phosphorus Incorporated in Silicon Nanocrystals as Function of Size

Defect-Induced Luminescence Quenching vs. Charge Carrier Generation of Phosphorus Incorporated in Silicon Nanocrystals as Function of Size

Intrinsic ultrasmall nanoscale silicon turns n-/p-type with SiO2/Si3N4-coating

Boron- and Phosphorus-Hyperdoped Silicon Nanocrystals

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Product

Resources

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Intrinsic ultrasmall nanoscale silicon turns n-/p-type with SiO₂/Si₃N₄-coating