Exploring the (Bi,Sb)₂(S,Se)₃ system for photovoltaics and SWIR sensors

Area of Science:

• Materials Science
• Semiconductor Physics
• Energy Conversion

Background:

• Bismuth (Bi) and antimony (Sb) chalcogenides, specifically (Bi,Sb)2(S,Se)3, are promising semiconductors.
• Their tunable band gaps, non-toxic elements, and low-temperature fabrication make them suitable for photovoltaic (PV) energy conversion and short-wavelength infrared (SWIR) to mid-infrared (MIR) sensors.
• Anisotropic opto-electrical properties necessitate control over crystallographic orientation for optimal device performance.

Purpose of the Study:

• To review synthesis routes and alloying strategies for (Bi,Sb)2(S,Se)3 materials.
• To investigate the relationship between directional growth and device efficiency.
• To prepare and characterize Bi-Sb-S-Se compositions for SWIR sensing and PV applications.

Main Methods:

• Synthesis of Bi-Sb-S-Se compositions via thermal evaporation of Sb2Se3, Bi2Se3, and Sb2S3 powders.
• Post-annealing treatments at various temperatures and atmospheres.
• Characterization using transmission and photoluminescence spectroscopy for band gap determination, and X-ray diffraction for phase analysis.

Main Results:

• Alloying Sb2S3 with Ag slightly decreased the band gap and modified microstructure.
• Alloying Sb2Se3 with Bi2Se3 aimed to reduce the band gap for SWIR applications (pure Sb2Se3 ≈1.17 eV).
• Band gap reduction was limited to ~0.9 eV due to limited Bi solubility in Sb2Se3, forming Bi2Se3 phases at higher Bi concentrations.

Conclusions:

• The study explored alloying strategies for (Bi,Sb)2(S,Se)3 semiconductors.
• Limited Bi solubility in Sb2Se3 restricted band gap tuning for SWIR applications.
• Initial device measurements demonstrated diode behavior and photoresponse, indicating potential for further optimization.