Small Polarons in Two-Dimensional Pnictogens: A First-Principles Study

Area of Science:

• Condensed Matter Physics
• Materials Science
• Computational Chemistry

Background:

• Two-dimensional (2D) pnictogen allotropes, such as blue and black phosphorene and arsenene, are promising materials for electronic applications.
• Understanding charge carrier behavior, specifically small polarons, is crucial for predicting and optimizing their electronic properties.

Purpose of the Study:

• To investigate the stability and characteristics of small polarons in blue phosphorene, black phosphorene, and arsenene using first-principles calculations.
• To elucidate the factors governing polaron localization and dynamics in these 2D materials.

Main Methods:

• First-principles density functional theory (DFT) calculations were employed.
• The study focused on hydrogen-passivated clusters and infinite size limits to analyze polaron behavior.
• Adiabatic polaron relaxation energies and motion barriers were computed.

Main Results:

• Small polarons exhibit charge localization and lattice distortions in both cationic and anionic clusters.
• Only hole polarons are stable in the infinite size limit for blue phosphorene.
• Adiabatic polaron relaxation energies are 0.1 eV for phosphorene and 0.15 eV for arsenene.
• Polarons localize on lone-pair orbitals, with half the charge spread over 13 atoms.
• Orbital hybridization in black phosphorene affects hole localization strength compared to blue phosphorene.
• Computed adiabatic barriers for polaron motion are small, suggesting barrierless movement.

Conclusions:

• Hole polaron stability is dependent on the specific allotrope, with blue phosphorene being favorable.
• The electronic structure, particularly lone-pair orbital behavior and hybridization, dictates polaron localization.
• The findings suggest that polarons can move with ease in these 2D materials, impacting their charge transport properties.