Gate-Induced Carrier Delocalization in Quantum Dot Field Effect Transistors

Turk, Michael E.; Choi, Jung Chan; Oh, Soong Ju; Fafarman, Aaron T.; Diroll, Benjamin T.; Murray, Christopher B.; Kagan, Cherie R.; Kikkawa, James M.

doi:10.1021/nl5029655

Cited by 25 publications

(26 citation statements)

References 44 publications

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“…Similar growth of ξ was observed in Ref. [3] for CdSe NCs.We also studied the effect of the NC separation to verify the theory prediction, Eq. (6).…”

supporting

confidence: 89%

“…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.…”

mentioning

confidence: 99%

“…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.…”

mentioning

confidence: 99%

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Metal–insulator transition in films of doped semiconductor nanocrystals

Chen¹,

Reich²,

Kramer³

et al. 2015

Nature Mater

109

134

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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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“…Similar growth of ξ was observed in Ref. [3] for CdSe NCs.We also studied the effect of the NC separation to verify the theory prediction, Eq. (6).…”

supporting

confidence: 89%

mentioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Metal–insulator transition in films of doped semiconductor nanocrystals

Chen¹,

Reich²,

Kramer³

et al. 2015

Nature Mater

109

134

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“…Besides, a small fraction of non-stoichiometric vacancies lead to a large concentration of carriers on the order of 10 20 cm −3 16,17 , which hampers the conductivity analysis 10,18,19 . Due to its close relationship with carrier transport, the analysis of field effect (the intrinsic effect of a transverse electric field on surface conductance) has been well practiced in MIT mechanisms including electron correlation (Mott transition) 20,21 and disorder (Anderson localization) 22,23 . Field effect studies of semiconductors have been a very active area of interest for many years, because they can probe the localized states of carriers which control the electronic properties of materials 24–26 .…”

Section: Introductionmentioning

confidence: 99%

Observation of carrier localization in cubic crystalline Ge2Sb2Te5 by field effect measurement

Qian

Tong

et al. 2018

Sci Rep

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The tunable disorder of vacancies upon annealing is an important character of crystalline phase-change material Ge2Sb2Te5 (GST). A variety of resistance states caused by different degrees of disorder can lead to the development of multilevel memory devices, which could bring a revolution to the memory industry by significantly increasing the storage density and inspiring the neuromorphic computing. This work focuses on the study of disorder-induced carrier localization which could result in multiple resistance levels of crystalline GST. To analyze the effect of carrier localization on multiple resistant levels, the intrinsic field effect (the change in surface conductance with an applied transverse electric field) of crystalline GST was measured, in which GST films were annealed at different temperatures. The field effect measurement is an important complement to conventional transport measurement techniques. The field effect mobility was acquired and showed temperature activation, a hallmark of carrier localization. Based on the relationship between field effect mobility and annealing temperature, we demonstrate that the annealing shifts the mobility edge towards the valence-band edge, delocalizing more carriers. The insight of carrier transport in multilevel crystalline states is of fundamental relevance for the development of multilevel phase change data storage.

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“…16,30 Here we employ time-resolved absorption (TRA) and photoluminescence (TRPL) spectroscopies to gain insight into the ligand exchange and annealing process through excited state dynamics. Because both TRA and TRPL implementations developed here are broadband with subpicosecond time resolution, we are able to show that exchanging aliphatic native ligands (NL) for thiocyanate (SCN) and subsequently annealing the samples increases electron trapping rates by 2 orders of magnitude.…”

mentioning

confidence: 99%

Ultrafast Electron Trapping in Ligand-Exchanged Quantum Dot Assemblies

et al. 2015

Self Cite

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We use time-integrated and time-resolved photoluminescence and absorption to characterize the low-temperature optical properties of CdSe quantum dot solids after exchanging native aliphatic ligands for thiocyanate and subsequent thermal annealing. In contrast to trends established at room temperature, our data show that at low temperature the band-edge absorptive bleach is dominated by 1S3/2h hole occupation in the quantum dot interior. We find that our ligand treatments, which bring enhanced interparticle coupling, lead to faster surface state electron trapping, a greater proportion of surface-related photoluminescence, and decreased band-edge photoluminescence lifetimes.

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Gate-Induced Carrier Delocalization in Quantum Dot Field Effect Transistors

Cited by 25 publications

References 44 publications

Metal–insulator transition in films of doped semiconductor nanocrystals

Metal–insulator transition in films of doped semiconductor nanocrystals

Observation of carrier localization in cubic crystalline Ge2Sb2Te5 by field effect measurement

Ultrafast Electron Trapping in Ligand-Exchanged Quantum Dot Assemblies

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