Metastable atomic-ordered configurations for Al_1/2Ga_1/2N predicted by Monte-Carlo method based on first-principles...

Area of Science:

• Materials Science
• Computational Materials Science
• Semiconductor Physics

Background:

• Recent experimental evidence highlights the metastability of Al_/12Ga_1-N (n= 2-10) with 1-2 monolayer in-plane configurations.
• Theoretical explanations for these metastable structures necessitate large calculation cells, which were a limitation in previous studies estimating local potential depth (Δσ) in ordered Al_1/2Ga_1/2N models.

Purpose of the Study:

• To theoretically explain the existence of metastable AlGaN structures.
• To overcome the limitations of small calculation cells in previous studies.
• To accurately estimate the local potential depth (Δσ) using large calculation cells.

Main Methods:

• Evaluation of large calculation cells based on interaction energies between proximate Al atoms (δE_Al-Al) in AlGaN alloys.
• Estimation of δE_Al-Al values using first-principles calculations (FPCs) with a (5a₁× 5a₂× 5c) cell.
• Survey of possible ordered configurations using various large calculation cell models combined with the Monte-Carlo method.
• Estimation of Δσ values by FPCs and comparison with existing configurations.

Main Results:

• The ordered configuration from the (4a₁× 2a₂× 1c) calculation cell (C₄₂) yielded the lowest Δσ of -9.3 meV/cation.
• This configuration exhibits an in-plane arrangement at the c(0001) plane with specific (-Al-Al-Ga-Ga-) and (-Al-Ga-) sequence arrangements along the m11-00 planes.
• Numerical calculations demonstrated consistency with experimentally observed morphology.

Conclusions:

• The study successfully evaluated large calculation cells to explain the metastability of AlGaN alloys.
• The identified C₄₂ configuration provides a theoretical basis for the observed in-plane metastable structures.
• The findings establish a strong correlation between computational predictions and experimental observations in AlGaN morphology.