Nanoscale compositional segregation in epitaxial AlScN on Si (111)

Area of Science:

• Materials Science
• Solid State Physics
• Thin Film Technology

Background:

• Aluminum nitride (AlN) is a key material for piezoelectric applications.
• Scandium (Sc) alloying in AlN is known to enhance piezoelectric and induce ferroelectric properties.
• Epitaxial thin films are crucial for fundamental material property investigations.

Purpose of the Study:

• To grow epitaxial wurtzite aluminum scandium nitride (AlScN) thin films on silicon substrates.
• To investigate the effects of scandium concentration on the structural and ferroelectric properties of AlScN.
• To explore the potential for self-assembled composition modulation in AlScN films.

Main Methods:

• Ultra-high vacuum reactive sputtering technique for film deposition.
• Growth of epitaxial AlScN thin films on Si (111) substrates.
• Systematic variation of Sc concentrations across a wide range.

Main Results:

• Successful growth of epitaxial wurtzite AlScN films on Si (111) with varying Sc content.
• Observation of increasing crystalline disorder and a wurtzite-to-rocksalt structural transition around 30 at% Sc.
• Detection of nanoscale compositional segregation (spinodal decomposition) at intermediate Sc concentrations.
• Correlation between lamellar features from composition fluctuations and polarization domains, influencing ferroelectric properties.

Conclusions:

• Epitaxial AlScN films on Si (111) can be fabricated, enabling structure-property studies.
• Scandium concentration critically affects AlScN's crystal structure, disorder, and ferroelectric behavior.
• Compositional segregation in AlScN can be harnessed to modulate ferroelectric properties and create self-assembled nanostructures.