Instability and Spontaneous Reconstruction of Few-Monolayer Thick GaN Graphitic Structures

Area of Science:

• Solid State Science and Technology
• Materials Science
• Condensed Matter Physics

Background:

• Two-dimensional (2D) semiconductors are a significant area of research.
• Planar structures were previously proposed for few-layer materials like gallium nitride (GaN) and zinc oxide (ZnO).
• Existing consensus suggested that nominally 3D tetrahedrally bonded semiconductors could form flat, few-layer structures.

Purpose of the Study:

• To investigate the structural stability of few-layer GaN.
• To challenge the existing consensus on planar few-layer semiconductor structures.
• To explore the electronic properties of reconstructed GaN phases.

Main Methods:

• Utilized first-principles calculations to simulate material structures and properties.
• Analyzed the structural reconstruction of few-layer GaN.
• Investigated the electronic band structure of the resulting phases.

Main Results:

• Demonstrated that the graphitic structure of few-layer GaN is unstable.
• Revealed spontaneous reconstruction into an 8|4 Haeckelite structure with covalent interlayer bonds.
• Observed a transformation of the band gap from indirect in planar GaN to direct in the Haeckelite phase.

Conclusions:

• The 8|4 Haeckelite structure represents a stable phase for few-layer GaN.
• The pronounced in-plane anisotropy and direct band gap of Haeckelite GaN are notable.
• Haeckelite few-layer GaN shows potential for applications in flexible nano-optoelectronics.