Adjusting the Energy Levels of HgTe and InAs Nanocrystals with Alkali Ions

The photodiode stack is the most effective design geometry for integrating colloidal nanocrystals (NCs) into optoelectronic devices dedicated to light emission and detection. Traditional designs rely on determining the absolute energy band alignment, followed by selecting suitable materials to transport charges (with energy levels resonant to the active material’s bands). Because of this method’s inherent limitations, we propose to explore an alternative approach where alkali metals are used to tune the absolute energy levels of the optically active layer. We illustrate this concept using lithium and cesium deposition onto narrow band gap NC films (i.e., HgTe and InAs), that are relevant materials for infrared optoelectronics. Our results show that work function shifts up to 0.9 eV can be achieved and that smaller alkalis are more effective at generating this shift. However, different behaviors are observed for HgTe and InAs. In the case of II–VI materials, the alkali acts as a pure dipole (i.e., no shift in the core level) and the film behaves as a bulk effective medium (i.e., no evidence of alkali intercalation). For III–V NCs, the alkali plays a dual role as both a dipole and a redox agent, making the alkali’s effect dependent on the NCs’ surface-to-volume ratio and the size of the alkali.

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Publication Details

Journal
The Journal of Physical Chemistry C
Published
2025-12-19
DOI
https://doi.org/10.1021/acs.jpcc.5c06879
Primary Topic
Quantum Dots Synthesis And Properties
Type
article
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article

Adjusting the Energy Levels of HgTe and InAs Nanocrystals with Alkali Ions

Mohamad Ibrahim, Peter Reiß, Mariarosa Cavallo, Marc Paye et al.
The Journal of Physical Chemistry C
Quantum Dots Synthesis And Properties
article

Adjusting the Energy Levels of HgTe and InAs Nanocrystals with Alkali Ions

Mohamad Ibrahim, Peter Reiß, Mariarosa Cavallo, Marc Paye, Emmanuel Lhuillier, Mathieu G. Silly, Debora Pierucci, Adrien Khalili, Erwan Bossavit, Dario Mastrippolito, J. Ávila, Yoann Prado, Sandrine Ithurria, James K. Utterback, Oleksandra Yeromina, Giorgia Strobbia, Jiho Roh
article en

Abstract

The photodiode stack is the most effective design geometry for integrating colloidal nanocrystals (NCs) into optoelectronic devices dedicated to light emission and detection. Traditional designs rely on determining the absolute energy band alignment, followed by selecting suitable materials to transport charges (with energy levels resonant to the active material’s bands). Because of this method’s inherent limitations, we propose to explore an alternative approach where alkali metals are used to tune the absolute energy levels of the optically active layer. We illustrate this concept using lithium and cesium deposition onto narrow band gap NC films (i.e., HgTe and InAs), that are relevant materials for infrared optoelectronics. Our results show that work function shifts up to 0.9 eV can be achieved and that smaller alkalis are more effective at generating this shift. However, different behaviors are observed for HgTe and InAs. In the case of II–VI materials, the alkali acts as a pure dipole (i.e., no shift in the core level) and the film behaves as a bulk effective medium (i.e., no evidence of alkali intercalation). For III–V NCs, the alkali plays a dual role as both a dipole and a redox agent, making the alkali’s effect dependent on the NCs’ surface-to-volume ratio and the size of the alkali.

The Journal of Physical Chemistry CVol. 130(1)
Centre National de la Recherche Scientifique (FR), Commissariat à l'Énergie Atomique et aux Énergies Alternatives (FR), Université Paris Sciences et Lettres (FR), Synchrotron soleil (FR), CEA Grenoble (FR), Sorbonne Université (FR), Laboratoire de Physique et d’Étude des Matériaux (FR), Institut de Recherche Interdisciplinaire de Grenoble (FR), Institut des NanoSciences de Paris (FR), Université Grenoble Alpes (FR)
Openalex Percentile: Top 66%
Quantum Dots Synthesis And Properties
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