Semiconductor-metal transition in Bi₂Se₃ caused by impurity doping

Area of Science:

• Condensed Matter Physics
• Materials Science
• Solid-State Chemistry

Background:

• Topological insulators like Bi₂Se₃ exhibit unique electronic properties.
• Impurity doping can significantly alter the electronic phase of materials.
• Understanding doping-induced transitions is crucial for novel electronic applications.

Purpose of the Study:

• Investigate the semiconductor-metal (S-M) transition in Ag-doped Bi₂Se₃ at 35 K.
• Elucidate the role of structural and electronic properties in this transition.
• Determine the factors governing the S-M transition mechanism.

Main Methods:

• Single-crystal X-ray diffraction (SC-XRD) for structural analysis.
• Hall effect measurements to probe carrier density and mobility.
• Electric-field effect measurements to analyze carrier behavior and Fermi level position.

Main Results:

• No structural transitions were observed; only slight lattice shrinkage occurred.
• Resistance reduction correlated with increased carrier density and mobility.
• Fermi level (E_F) was found near the bulk conduction band (BCB), with higher bulk mobility than surface mobility.
• Asymmetric field-effect mobility indicated E_F proximity to the BCB.

Conclusions:

• The S-M transition in Ag-doped Bi₂Se₃ is primarily an electronic phenomenon, not structurally driven.
• Fermi level pinning at the BCB is critical for inducing the transition.
• The transition can be triggered by Fermi level depinning or bulk-surface transport crossover.