Wurtzite AlN(0001) Surface Oxidation: Hints from Ab Initio Calculations.

Area of Science:

• Materials Science
• Surface Science
• Computational Materials Science

Background:

• Aluminum nitride (AlN) possesses excellent electrical and thermal properties, leading to diverse applications.
• AlN's susceptibility to oxidation at elevated temperatures presents a significant challenge, hindering its widespread use.
• The fundamental physics governing AlN surface oxidation remains poorly understood.

Purpose of the Study:

• To investigate the atomic-level mechanisms of wurtzite AlN(0001) surface oxidation.
• To elucidate the role of oxygen adsorption sites and coverage on the oxidation process.
• To understand the formation of oxidation products and potential phase transformations.

Main Methods:

• First-principles calculations were employed to simulate the oxidation process.
• Calculations focused on adsorption energies of oxygen on the AlN(0001) surface.
• Analysis included the identification of dominant gas products and intermediate structures.

Main Results:

• Oxygen adsorption is site-dependent, with preferential adsorption at the H3 hollow site across various oxygen coverages.
• Nitrogen gas (N2) is the primary gaseous product, with nitrogen vacancies (VN) forming sequentially.
• Nitrogen vacancies accelerate AlN oxidation, facilitating oxygen incorporation and forming an O-Al-O layer, a precursor to gamma-alumina (γ-Al2O3).

Conclusions:

• The study provides atomic-level insights into the AlN oxidation mechanism, highlighting the role of nitrogen vacancies.
• The formation of an O-Al-O layer suggests a pathway towards γ-Al2O3 formation.
• A potential mechanism for the phase transformation from γ-Al2O3 to α-Al2O3 was proposed based on the simulations.