Coherent-interface-induced strain in large lattice-mismatched materials: A new approach for modeling Raman shift

Area of Science:

• Materials Science
• Solid State Physics
• Spectroscopy

Background:

• Strain engineering is crucial for tuning optical and electronic properties of III-nitrides.
• Accurate strain investigation methods are essential for reliable material property tuning.
• Current Raman spectroscopy models for strain in GaN and AlN are limited in accuracy.

Purpose of the Study:

• To evaluate the validity of the linear Raman model for strain in GaN and AlN.
• To develop a new, more accurate model for strain-induced Raman frequency shifts in GaN and AlN.
• To propose a novel approach for correlating Raman shifts with strain in epitaxial layers.

Main Methods:

• Experimental Raman spectroscopy on GaN and AlN under varying biaxial strains.
• Development of a new non-linear model for strain-induced Raman frequency shifts.
• Analysis of lattice coherency in superlattice structures.

Main Results:

• The widely used linear Raman model is found to be invalid for GaN and AlN beyond small biaxial strains (< 0.2%).
• Discrepancy between experimental and calculated strain values increases with strain magnitude.
• A new model accurately describes strain-induced Raman shifts for strains up to 2.5% in GaN and AlN.

Conclusions:

• The linear Raman model is insufficient for comprehensive strain analysis in GaN and AlN.
• A new model provides accurate strain determination over a wider range of biaxial strains.
• The proposed lattice coherency approach offers a versatile method for strain-Raman shift correlation in epitaxial materials.