Infrared Imaging Using Thermally Stable HgTe/CdS Nanocrystals

Area of Science:

• Materials Science
• Nanotechnology
• Optoelectronics

Background:

• Mercury telluride (HgTe) nanocrystals offer tunable infrared optical properties but suffer from instability during processing and operation.
• Low-temperature synthesis, while energy-efficient, promotes particle sintering and aggregation, degrading performance.
• Joule heating in readout circuits further exacerbates particle aggregation, leading to poor optical edge definition and high dark current.

Purpose of the Study:

• To improve the thermal stability and operational performance of HgTe nanocrystals for infrared applications.
• To investigate the impact of cadmium sulfide (CdS) shelling on HgTe nanocrystal properties.
• To enhance the external quantum efficiency and long-term stability of infrared imagers utilizing modified HgTe nanocrystals.

Main Methods:

• Synthesis of HgTe nanocrystals followed by atomic layer deposition of CdS shells.
• Thermal annealing and characterization of shelled and unshelled nanocrystals.
• k.p self-consistent simulations to determine electronic structure and exciton binding energy.
• Fabrication and testing of infrared imagers incorporating the modified nanocrystals.

Main Results:

• CdS shelling imparts significant thermal stability, preventing redshift upon annealing and reducing amalgamation.
• Photoconductivity is preserved after atomic layer deposition, and the material exhibits p-type behavior.
• Exciton binding energy is calculated to be approximately 200 meV.
• Infrared imagers achieve 40% external quantum efficiency with enhanced long-term stability.

Conclusions:

• CdS shelling is a viable strategy to overcome the instability issues of HgTe nanocrystals.
• The improved material properties enable higher performance and reliability in infrared imaging devices.
• This work paves the way for practical applications of spectrally tunable HgTe-based infrared technologies.