Oxygen impurity effects on the piezoelectric response of wurtzite Al0.625Sc0.375N

Abstract

Al1−xScxN thin films have attracted remarkable attention in industrial applications, including micro-electro-mechanical systems and radio frequency acoustic filters due to their excellent piezoelectric properties and processing compatibility. However, a major challenge in developing high-performance Al1−xScxN thin films lies in controlling persistent oxygen impurities. Here, we systematically investigate the impact of oxygen impurities on the structural stability and piezoelectric properties of experimentally reported wurtzite Al0.625Sc0.375N using first-principles calculations. Seventeen types of defect configurations incorporating oxygen defects and cation vacancies have been developed, providing critical insights into their formation energies, effective piezoelectric coefficient (d33,f), dielectric constant (ɛ33), and electromechanical coupling coefficient (K332). Our findings demonstrate that moderate oxygen doping, particularly oxygen substitutional defects (ON), enhances the coefficient d33,f primarily attributed to a reduction in the elastic constant C33 and an increase in the piezoelectric tensor e33. In contrast, the interstitial oxygen (Oi) and cation vacancies (VAl/Sc) tend to decrease d33,f. Moreover, a low concentration pure ON at about 1.6% can notably enhance d33,f and K332 compared to oxygen-free w-Al0.625Sc0.375N and a higher concentration of ON defects increases ɛ33, further boosting the electric field response along the c-axis. These insights into defect engineering in Sc-doped AlN provide promising strategies for enhancing piezoelectric performance.