Reliability and Stability Issues in Bi2O2Se/β-Bi2SeO5 Field-Effect Transistors

The layered semiconductor Bi2O2Se is a promising candidate for next-generation nanoelectronic devices because it combines favorable electronic and structural properties. These include an exceptionally high electron mobility, a suitable bandgap and air stability, and most importantly, the ability to form a high-κ native oxide, Bi2SeO5 (with a calculated bulk κ > 30). However, intrinsic point defects in the semiconductor and the oxide can influence the electronic behavior and long-term reliability. In this work, we employ density functional theory to investigate the electronic structure, formation energies, trap levels, and relaxation energies of the relevant native defects in both Bi2O2Se and β-Bi2SeO5. Our results demonstrate that selenium and oxygen vacancies in the semiconductor Bi2O2Se act as shallow donors, donating free electrons to the conduction band, consistent with the commonly observed unintentional n-type conductivity. In contrast, oxygen vacancies in the dielectric β-Bi2SeO5 introduce deep-level trap states, indicating that they may act as performance-limiting charge trapping centers during device operation. We successfully correlate these theoretically identified defects with experimental device measurements from a prototype Bi2O2Se/β-Bi2SeO5 field-effect transistor, structurally characterized via scanning transmission electron microscopy. We finally demonstrate the contribution of defects to critical reliability issues, specifically hysteresis and bias temperature instability. These insights provide input for reliability modeling and defect engineering strategies for improving the long-term stability of Bi2O2Se/Bi2SeO5-based nanoelectronics.