Huan He

Displacement cascades induced by ion implantation are a crucial process for fabricating color centers in 4H-silicon carbide, while the differences in defect formation and evolution at hexagonal and cubic lattice sites are often overlooked. In this study, molecular dynamics simulations were employed to systematically investigate the site-dependent formation and evolution of point defects and divacancies in 4H-silicon carbide. The results indicate that the stable number of displaced atoms at cubic sites is significantly higher than that at hexagonal sites, primarily driven by carbon displaced atoms, whereas vacancy concentrations show no substantial site difference. This behavior is attributed to the lower threshold displacement energy of cubic carbon atoms (∼30.19 eV) relative to hexagonal carbon atoms (∼33.31 eV), together with a site-exchange recombination process amplifying the displaced-atom disparity while narrowing the vacancy disparity. Moreover, the divacancies generated during the initial cascades are highly unstable, with approximately 80% undergoing recombination. Among the surviving stable divacancies, the production of basal configurations is significantly higher than that of axial configurations. This study provides critical data for developing site-resolved radiation damage models in 4H-SiC and offers valuable microscopic theoretical insights into the fabrication of solid-state quantum color centers via ion irradiation.

This work systematically unveils the nanoscale surface damage dynamics in gallium nitride by investigating the atomistic mechanisms of hillock formation. The results identify two distinct hillock morphologies dependent on electronic energy loss (Se) values. Bell-shaped hillocks form under 18.2 keV/nm Kr irradiation, whereas crater-rim hillocks with central holes emerge under 40.2 keV/nm Ta irradiation. Microstructural analysis reveals that Ga-rich hillocks are accompanied by the generation of metastable zincblende nanodomains. These nanodomains preferentially aggregate around the periphery or sidewalls of the hillocks and exhibit a high spatial correlation with screw dislocations. Further temperature-dependent studies indicate that elevated temperatures significantly enlarge the overall dimensions of the hillock structures without altering their fundamental morphologies. Notably, under Ta irradiation above 1200 K, the high temperatures drastically reduce the viscosity and surface tension of liquid gallium. This enhanced fluidity of the transient molten phase promotes the formation of penetrating nanochannels.

Swift heavy ion (SHI) irradiation has long been used to evaluate the performance of radiation-hard semiconductor devices. However, the in-depth insight into its microscopic processes and damage evolution remains unclear. In this work, the ultrafast microscopic processes within femtosecond timescales under SHI irradiation of four typical semiconductor materials (Si, 4H-SiC, GaN, β-Ga2O3) are investigated by the coupling ab initio and two-temperature model (TTM) methods. The ab initio method is utilized to systematically calculate the temperature-dependent electronic thermodynamic parameters of four semiconductor materials and then incorporated into the TTM to reveal the significance of the intrinsic thermodynamic properties on thermal spike evolution under SHI irradiation. The results demonstrate that stronger electron–phonon coupling accelerates femtosecond thermal processes and promotes more efficient energy transfer from the electronic to lattice subsystems. Lower thermal conductivity suppresses energy diffusion within subsystems, leading to more pronounced energy spikes. These energy spikes induced by the SHI produce instantaneous molten zones where radius variations are correlated with the material melting threshold energy. Under 430 MeV Kr ion irradiation, instantaneous molten zones with radii of 4.64 and 5.70 nm are formed within femtoseconds in GaN and β-Ga2O3, respectively, while no melting occurs in Si or SiC. This work provides essential data for understanding the behavior and microscopic damage processes of semiconductor materials under extreme irradiation conditions.

The microscopic origin of random telegraph noise (RTN) in semiconductor devices remains a subject of debate. Previous studies proposed several hypotheses involving phosphorus–vacancy center and oxygen–vacancy centers, while recent experimental evidence indicates that it may be due to electrically active defects formed by the addition of carbon. In this work, first-principles calculations based on density functional theory are performed to systematically investigate the structural configurations, formation energetics, charge-state transition levels, and migration behaviors of carbon-related defects. Both carbon interstitial (Ci) and CiCs pairs exhibit multiple metastable configurations with distinct charge-state transition levels, leading to pronounced variations in their contribution to carrier recombination. Furthermore, the low migration barriers between metastable states suggest frequent structural conversions, which provide a mechanistic explanation for the two-level RTN behaviors observed in experiments. By directly correlating atomistic defect behavior and macroscopic RTN characteristics, this study provides a fundamental framework for understanding defect-induced RTN in semiconductor devices. These findings provide an essential theoretical foundation for the development of strategies to suppress RTN in advanced semiconductor technologies.

This study employs two-temperature molecular dynamics simulations to investigate swift heavy ion irradiation of SiO2 substrate-supported two-dimensional material graphene. Material-dependent electronic and thermal properties are integrated into each region to model the energy transfer between the electronic and atomic subsystems of the studied materials. Simulations of interactions with Xe heavy ions are performed with ion kinetic energies ranging from 0.5 to 25 GeV with electronic stopping powers from ∼2.6 to 17.7 keV/nm. With the studied ion energy range, nanopores with a diameter of up to 5 nm can be formed in graphene due to the thermally driven sputtering effect, while amorphization occurs along the ion track in the SiO2 substrate. The coupling between the substrate and two-dimensional material significantly impacts the structural change due to heat transfer and atomic interactions among different layers of materials. The method applied in this work provides a valuable tool for modeling and understanding the structural modifications induced by ion irradiation in layered structures.

Understanding the properties of defects is crucial to design higher performance semiconductor materials because they influence the electronic and optical properties significantly. Using ab initio calculations, the dynamics properties of nitrogen interstitial in GaN material, including the configuration, migration, and interaction with vacancy were systematically investigated in the present work. By introducing different sites of foreign nitrogen atom, the most stable configuration of nitrogen interstitial was calculated to show a threefold symmetry in each layer and different charge states were characterized, respectively. In the researches of migration, two migration paths, in-plane and out-of-plane, were considered. With regards to the in-plane migration, an intermediated rotation process was observed first time. Due to this rotation behavior, two different barriers were demonstrated to reveal that the migration is an anisotropic behavior. Additionally, charged nitrogen Frenkel pair was found to be a relatively stable defect complex and its well separation distance was about 3.9 Å. Part of our results are in good agreement with the experimental results, and our work provides underlying insights of the identification and dynamics of nitrogen interstitial in GaN material. This study of defects in GaN material is useful to establish a more complete theory and improve the performance of GaN-based devices.