- The full article entitled “Quantification of interfacial trap states via bias-applied HAXPES: a chemical-state perspective” can be found at the Journal of Materials Chemistry C website at https://doi.org/10.1039/D5TC01375E
- Authors: Wen-Jen Chen, Yin-Bo Tseng, and Hsiu-Wei Cheng*
Understanding how trapped charges behave at solid–solid interfaces is crucial for next-generation semiconductor and nanoelectronic devices. When two solids meet, discontinuity in their electronic structures often creates localized trap states that govern charge accumulation and transport. Conventional electrical analyses—such as C–V or DLTS—quantify trap densities but cannot chemically resolve atomic-level origins.
This study introduces a bias-applied hard X-ray photoelectron spectroscopy (BA-HAXPES) method to directly monitor oxidation-state changes at buried Si | SiO₂ | Au interfaces under real-time electrical bias. Prof. Hsiu-Wei Cheng and his team demonstrate that traditional interpretations that based on peak shifts overlook effects of dielectric thickness in the MOS system. By incorporating a modified Grahame-equation framework, they establish that peak intensity variations provide a more reliable measure of trap-state activity than simple binding-energy shifts.
The bias-dependent spectra reveal distinct charge behaviors at the interface. Under applied bias, the Si³⁺ states exhibit potential-driven delocalization, behaving similarly to mobile carriers within the dielectric layer, while the Si²⁺ states remain tightly confined at the SiO₂|Au interface, serving as localized molecular-scale trap signatures. It should be noted that these oxidation-state labels do not indicate real redox reactions but rather represent differences in local chemical environments associated with interfacial charging. Together, these findings quantitatively link the evolution of chemical-state features to charge accumulation, offering a chemical-state perspective for understanding and engineering trap states. This approach provides molecular-level insight into charge dynamics in MOS structures and establishes a foundation for the precise design of next-generation nanoscale electronic devices.
