Atomic and electronic structure of Lomer dislocations at CdTe bicrystal interface

Area of Science:

• Materials Science
• Solid State Physics
• Semiconductor Physics

Background:

• Extended defects, such as dislocations, critically influence semiconductor electronic properties.
• In photovoltaics (PVs), these defects can enhance electron-hole recombination, reducing efficiency.
• Understanding and controlling defects in materials like Cadmium Telluride (CdTe) is crucial for advancing solar cell technology.

Purpose of the Study:

• To investigate the atomic structure and electronic properties of dislocations in CdTe grain boundaries.
• To analyze the impact of these defects on charge transport and recombination.
• To explore the potential of chlorine (Cl) doping to mitigate detrimental defect effects in CdTe.

Main Methods:

• Fabrication of model CdTe bicrystal systems using wafer bonding to create controlled grain boundaries.
• Atomic-resolution scanning transmission electron microscopy (STEM) for interface structural analysis.
• Geometrical phase analysis (GPA) for strain mapping.
• Density functional theory (DFT) modeling for electronic structure calculations of dislocation cores.

Main Results:

• Identification of three distinct Lomer dislocation types at a [1-10]/(110) 4.8° tilt grain boundary in CdTe.
• DFT calculations revealed significant mid-gap states and varying charge-channeling tendencies within dislocation cores.
• Chlorine (Cl) doping effectively reduced mid-gap states while preserving beneficial charge separation effects.

Conclusions:

• Controlled fabrication of CdTe bicrystal interfaces enables systematic atomic-scale analysis of grain boundary effects.
• Dislocations in CdTe introduce electronic states that can be modified by doping.
• These findings provide new strategies for optimizing CdTe solar cells by managing grain boundary defects.