Effective band structure of random alloys

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Materials Science

Background:

• Random substitutional alloys (A(x)B(1-x)) lack translational symmetry, precluding traditional band structure analysis.
• Experimental interpretations often rely on concepts like effective masses and van Hove singularities, derived from wave vector (k) constructs.
• A method is needed to describe the electronic properties of disordered alloys.

Purpose of the Study:

• To develop and apply a method for calculating an effective band structure (EBS) for random substitutional alloys.
• To investigate how alloy composition affects electronic band characteristics.
• To analyze the electronic properties of specific alloy systems, (In,Ga)N and Ga(N,P).

Main Methods:

• Utilized large supercells with randomly distributed A and B atoms.
• Employed spectral decomposition to transform supercell eigenstates into an effective band structure (EBS) within the primitive cell.
• Analyzed the EBS at various compositions, band indices, and k-points.

Main Results:

• The effective band structure (EBS) successfully describes electronic properties in disordered alloys.
• In (Indium,Gallium)Nitride ((In,Ga)N), the EBS shows rapid disintegration of valence band Bloch character with increasing alloy disorder.
• In Gallium (Nitrogen,Phosphorus) (Ga(N,P)), the EBS reveals the emergence of a pinned impurity band.

Conclusions:

• The effective band structure (EBS) approach provides a viable framework for understanding electronic properties in random alloys.
• This method highlights the composition-dependent loss of band characteristics in (In,Ga)N and the formation of impurity states in Ga(N,P).
• The findings offer insights into the electronic behavior of technologically relevant semiconductor alloys.