Toward a Unified Theory Correlating Electronic, Thermodynamic, and Mechanical Properties at Defective Al/SiO2 Nanodevice Interfaces: An Application to Dielectric Breakdown

We study the electronic structure and local pressure of Al/crystal-SiO2 (Al/c-SiO2) and Al/amorphous-SiO2 (Al/a-SiO2) interface systems in the presence of oxygen vacancy. In this modeled nanodevice, we created an oxygen vacancy at different sites from the interface to the quasi-bulk SiO2 region in both neutral and charged Al/SiO2 systems. We found that oxygen vacancies close to the interface do not change the band offset or electronic structures. However, oxygen vacancies far away from the interface generate shallow hole trapping states. We also applied the quantum stress density theory to calculate the local hydraulic pressure around each host oxygen atom to be removed for creating an oxygen vacancy. We found a correlation between vacancy formation energy and the oxygen local pressure, which is consistent with the previous study in the bulk a-SiO2. We also found that oxygen atoms close to the interface have similar to 0.9 eV lower formation energy and lower local pressure. In addition, charges (-1 e and +1 e) have been introduced to Al/SiO2 systems in the presence of oxygen vacancies to study the doping effect on the electronic structures. It shows that charging the Al/SiO2 systems varies the Fermi energy level and reduces the potential barrier height of the charge carriers, hence decreasing the oxide dielectric strength. We further explore the relation between electron hopping integrals and the oxygen vacancies in the charged systems. Our result shows that the hopping integrals increase significantly when their hopping paths are closer to the oxygen vacancies, e.g., the higher the hopping integral, the higher the formation energy of vacancies, which also correspond to lower local pressure around the removed oxygen atoms. Our data also suggest strong correlations among local pressure, vacancy formation energy, electronic potential barrier height, and electronic hopping integrals, providing a unique yet comprehensive understanding of electronic properties on the metal/oxide interface. Our research represents an important milestone in the ultimate goal of an advanced understanding of dielectric breakdown.