Electromechanical coupling in Yb-substituted III-V nitride alloys

Abstract

Yb-substitution induced enhancement for electromechanical coupling in wurtzite III-V nitrides is studied via theoretical calculations and experiments. The substitution induced local strain and mechanical softening enhanced electromechanical coupling. Interestingly, mechanical softening induced by Yb substitution shows less dependence on the parent AlN and GaN, which is considered to originate from the Yb-Yb pair interaction. The difference in enhancement of electromechanical coupling for the alloys mainly comes from the enhanced piezoelectric response. Spontaneous polarization induced by the strain plays a key role in enhancing the piezoelectric response, which can be improved by selecting the wurtzite structure with an optimized internal parameter. Additionally, when the substitutional element has significantly different ionic size from the host cation, the piezoelectric response due to the internal strain is considerably enhanced. This can serve as a simple guideline to identify alloying components in a search for a massive increase in electromechanical coupling.