Charge transport and positively charged defects in Ta2O5/SiO2 dielectric stacks

The electrical properties of Ta2O5/SiO2 stack structures are investigated, focusing on charge transport and the presence of positively charged defects. Capacitance–voltage (C–V) and triangular voltage sweep measurements revealed the existence of positively charged defects, which influence the electrical behavior of the stack. The origin of the defects is discussed with emphasis on the possible incorporation of alkali ions in Ta2O5. The current–electric field (J–E) characteristics were analyzed using hopping conduction, Poole–Frenkel emission, and Fowler–Nordheim (FN) tunneling models, demonstrating that hopping and FN tunneling adequately describe the experimental data at moderate and high electric fields, respectively. Fitting of the J–E data yielded physically reasonable parameters, including hopping distances of 1.1–1.5 nm, activation energies around 0.9 eV, and FN barrier heights of approximately 2 eV, consistent with known SiO2 and Ta2O5 interfaces. The results indicate that electron transport in these stacks is primarily controlled by the SiO2 layer and the SiO2/Ta2O5 interface, while the Ta2O5 layer contributes traps that facilitate field-assisted hopping. These findings provide insight into the interplay between trap states and tunneling mechanisms in high-k oxide stacks and are relevant for the optimization of dielectric stacks in electronic devices.