n- and p-Type HgTe Quantum Dot Films

Electronic doping is one of the most important experimental capabilities in all of semiconductor research and technology. Through electronic doping, insulating materials can be made conductive, opening doors to the formation of p-n junctions and other workhorses of modern semiconductor electronics. Recent interest in exploiting the unique physical and photophysical properties of colloidal semiconductor nanocrystals for revolutionary new device technologies has stimulated efforts to prepare electronically doped colloidal semiconductor nanocrystals with the same control as available in the corresponding bulk materials. Despite the impact that success in this endeavor would have, the development of general and reliable methods for electronic doping of colloidal semiconductor nanocrystals remains a long-standing challenge. In this Account, we review recent progress in the development and characterization of electronically doped colloidal semiconductor nanocrystals. Several successful methods for introducing excess band-like charge carriers are illustrated and discussed, including photodoping, outer-sphere electron transfer, defect doping, and electrochemical oxidation or reduction. A distinction is made between methods that yield excess band-like carriers at thermal equilibrium and those that inject excess charge carriers under thermal nonequilibrium conditions (steady state). Spectroscopic signatures of such excess carriers, accessible by both equilibrium and nonequilibrium methods, are reviewed and illustrated. A distinction is also proposed between the phenomena of electronic doping and redox-potential shifting. Electronically doped semiconductor nanocrystals possess excess band-like charge carriers at thermal equilibrium, whereas redox-potential shifting affects the potentials at which charge carriers are injected under nonequilibrium conditions, without necessarily introducing band-like charge carriers at equilibrium. Detection of the key spectroscopic signatures of band-like carriers allows distinction between these two regimes. Both electronic doping and redox-potential shifting can be powerful tools for tuning the performance of nanocrystals in electronic devices. Finally, key chemical challenges associated with nanocrystal electronic doping are briefly discussed. These challenges are centered largely on the availability of charge-carrier reservoirs with suitable redox potentials and on the relatively poor control over nanocrystal surface traps. In most cases, the Fermi levels of colloidal nanocrystals are defined by the redox properties of their surface traps. Control over nanocrystal surface chemistries is therefore essential to the development of general and reliable strategies for electronically doping colloidal semiconductor nanocrystals. Overall, recent progress in this area portends exciting future advances in controlling nanocrystal compositions, surface chemistries, redox potentials, and charge states to yield new classes of electronic nanomaterials with attractive physical properties and the potenti...

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“…25 Injection of both carrier types has also been observed in the spectroelectrochemistry of HgTe nanocrystal films. 26 …”

Section: Electronic Absorption Spectroscopymentioning

confidence: 99%

Electronic Doping and Redox-Potential Tuning in Colloidal Semiconductor Nanocrystals

et al. 2015

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“…The use of an electrochemical cell to study novel optical properties, such as intraband optical transitions in the IR region,b leaching of the interband visible excitations, andt he band-edge PL arising upon heavy charging of CQDsi sw ell described in as eries of works reported by Guyot-Sionnest et al for cadmium, lead, and mercury chalcogenide CQDs. [66,67,124,125] Such electrochemical studies have also revealed that charging of CQD films with electrons filling their conduction-bande dge may result in increasedc onductivity of the films, [124] as well as quick corrosion of the dots, owing to consumption of the extra electrons in the electrochemical reactions taking place at the surfaceo ft he dots. [62] The use of an electrochemical cell for charging CQDs has provided avaluablemethod forinvestigatingt he various implications of chargingC QDs;h owever,i ti sn ot practical for utilizing the effects of doping in optoelectronic applications.T owards that prospect, remote doping by charge-donating molecules attached to the surface of the dots is am ore promising approach.…”

Section: Remotedopingmentioning

confidence: 99%

Strategies for the Controlled Electronic Doping of Colloidal Quantum Dot Solids

Stavrinadis

Konstantatos

2016

ChemPhysChem

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Over the last several years tremendous progress has been made in incorporating colloidal quantum dot (CQD) solids as photoactive components in optoelectronic devices. A large part of this progress is associated with significant advancements made in controlling the electronic doping of CQD solids. Today, a variety of strategies exists towards that purpose; this Minireview aims to survey the major published works in this subject. Additional attention is given to the many challenges associated with the task of doping CQDs, as well as to the realization of optoelectronic functionalities and applications upon successful light and heavy electronic doping of CQD solids.

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“…In contrast to chemical methods, thermodynamic control of doping has been achieved using electrochemical methods, which shift the Fermi level of the nanocrystal solid through reversible charge transfer from the electrode. [12][13][14][15][16] Fine control over the applied potential (± 1 mV) allows the doping level to be set with precision. Despite this advantage, electrochemical doping methods are not suited to large area solution processing of nanocrystal solids and require specialized equipment.…”

mentioning

confidence: 99%

Controlled Chemical Doping of Semiconductor Nanocrystals Using Redox Buffers

2012

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Semiconductor nanocrystal solids are attractive materials for active layers in next-generation optoelectronic devices; however, their efficient implementation has been impeded by the lack of precise control over dopant concentrations. Herein we demonstrate a chemical strategy for the controlled doping of nanocrystal solids under equilibrium conditions. Exposing lead selenide nanocrystal thin films to solutions containing varying proportions of decamethylferrocene and decamethylferrocenium incrementally and reversibly increased the carrier concentration in the solid by 2 orders of magnitude from their native values. This application of redox buffers for controlled doping provides a new method for the precise control of the majority carrier concentration in porous semiconductor thin films.

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n- and p-Type HgTe Quantum Dot Films

Cited by 60 publications

References 23 publications

Electronic Doping and Redox-Potential Tuning in Colloidal Semiconductor Nanocrystals

Electronic Doping and Redox-Potential Tuning in Colloidal Semiconductor Nanocrystals

Strategies for the Controlled Electronic Doping of Colloidal Quantum Dot Solids

Controlled Chemical Doping of Semiconductor Nanocrystals Using Redox Buffers

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