Temperature-induced absolute energy shift of the electronic spectrum in HgTe nanocrystals

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Abstract
Mercury telluride (HgTe) nanocrystals (NCs) are promising materials for infrared photodetection due to their size-tunable band edges and compatibility with colloidal synthesis. While optical studies have established the temperature dependence of their relative bandgaps, the evolution of their absolute electronic spectrum with cooling remains poorly understood, despite its critical role in the device operation. In this work, we investigate in situ the temperature-induced absolute energy shift of HgTe NCs' electronic states with varying band edge energies, using X-ray photoemission spectroscopy. We observe a systematic and reversible rigid shift of core levels toward lower binding energies upon cooling, reaching approximately 80 meV per 100 K, four times larger than the corresponding optical band edge shift (≈20 meV). This behavior is consistent across different NC sizes, making the impact more dramatic for the narrower bandgap NCs. Such absolute energy shifts can significantly alter carrier densities and interfacial band alignments, potentially creating Schottky barriers and reducing extraction efficiency in photodiode architectures. Our findings highlight the necessity of accounting for temperature-induced absolute energy shifts in the design of next-generation HgTe NC-based infrared detectors.
Funding Information
  • European Research Council (ERC grant AQDtive (grant n{degree sign}101086358))
  • Agence Nationale de la Recherche (MixDferro (ANR-21-CE09-0029))
  • Agence Nationale de la Recherche (Quicktera (ANR-22-CE09-0018))
  • Agence Nationale de la Recherche (Operatwist (ANR-22-CE09-0037-01))
  • Agence Nationale de la Recherche (E-map (ANR-23-CE50-0025))
  • Agence Nationale de la Recherche (DIRAC (ANR-24-ASM1-0001))
  • Agence Nationale de la Recherche (camIR (ANR-24-CE42-2757))
  • Agence Nationale de la Recherche (Piquant (ANR-24-CE09-0786).)
  • Region Ile de France (Sesame INSIDE)
  • Institut de physique (MITI within)
  • RENATECH (renatech+)

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