Hyeon-Kyun Noh

O-vacancy as the origin of negative bias illumination stress instability in amorphous In–Ga–Zn–O thin film transistors

We find that O-vacancy (VO) acts as a hole trap and plays a role in negative bias illumination stress instability in amorphous In–Ga–Zn–O thin film transistors. Photoexcited holes drift toward the channel/dielectric interface due to small potential barriers and can be captured by VO in the dielectrics. While some of VO+2 defects are very stable at room temperature, their original deep states are recovered via electron capture upon annealing. We also find that VO+2 can diffuse in amorphous phase, inducing hole accumulation near the interface under negative gate bias.

Local bonding effect on the defect states of oxygen vacancy in amorphous HfSiO4

We perform first-principles calculations to investigate the defect properties of O vacancies in amorphous HfSiO4. For atomic models generated from molecular dynamics simulations, we find that O vacancies, which have only Hf atoms or a mixture of Hf and Si in the neighborhood, behave as charge trap centers, similar to those in HfO2. On the other hand, O vacancies surrounded by only Si atoms are energetically most favorable and have very high trap energies for both electron and hole carriers. Thus, these defects are suggested to be responsible for the reduction of threshold voltage instability.

First-principles study of Si CMOS materials and nanostructures

The technology roadmap reflects that complementary metal-oxide-semiconductor field-effect transistors based on silicon will reach absolute limits on its performance within the next decade. In microelectronics, quantum effects become important and the device performance is very sensitive to defects at or close to interfaces. To improve the device operation, it is urgent to understand materials, defects, and interface properties at the atomic level. First-principles calculations, based on the density functional theory, enable us to investigate important aspects of the physics of materials and structures. We will discuss successful applications and limitations of the modern computational techniques, such as the standard generalized gradient approximation, hybrid density functional, and quasiparticle energy calculations, for the electronic and transport properties and the role of defects in Si CMOS devices with Si/high-k and metal/high-k interfaces.

The Electronic Structure of Oxygen Vacancy in Amorphous HfSiO4

We perform first‐principles density functional calculations to investigate the electronic structure of O‐vacancy in amorphous HfSiO4. We find that O‐vacancies surrounded only by Si atoms are energetically most favorable and exhibit the defect levels similar to those of α‐quartz SiO2. When O‐vacancies have a mixture of Si and Hf atoms or only Hf atoms in the neighborhood, they behave as charge traps, similar to those in HfO2. We suggest that Si‐surrounded O‐vacancy defects play a role in improving the threshold voltage instability in HfSiO4‐based metal‐oxide‐semiconductor devices.