arXiv subjects

Sofia Apergi

Publications and source records attributed to Sofia Apergi.

6 recordsLinked to original sources

arXiv2026

The impact of interfacial chemistry on the band offset of GaAs/Ga$_2$O$_3$ heterostructures

Ga$_2$O$_3$/GaAs heterojunctions are emerging as promising candidates for next-generation power electronics, photonics, and energy devices, leveraging the high breakdown voltage and thermal stability of Ga$_2$O$_3$ alongside the mature technology, high hole mobility, and higher refractive index of GaAs. The efficiency of these devices depends strongly on the band alignment between the two materials, however both type-I and type-II alignment have been reported in the literature for these heterostructures. To address this ambiguity, we use hybrid density functional theory to systematically investigate the band alignment at GaAs/Ga$_2$O$_3$ interfaces, focusing on the role of interface chemistry. By considering Ga-O-, As-, and As-O-rich interfaces both in amorphous and crystalline Ga$_2$O$_3$ phases, we demonstrate that interface stoichiometry determines the alignment type: Ga-O-rich interfaces exhibit type-II alignment with large valence band offsets (~3.1 eV), while As-rich and As-O-rich interfaces favor type-I alignment with reduced offsets (~2.3-2.6 eV). These trends are attributed to interface dipole formation driven by bonding configuration. Our findings provide insight into the relationship between chemistry and band alignment in GaAs/Ga$_2$O$_3$ heterostructures, enabling targeted optimization for specific device applications.

cond-mat.mtrl-sci↗

arXiv2025

Full ab initio atomistic approach for morphology prediction of hetero-integrated crystals: A confrontation with experiments

Here, we propose a comprehensive first-principle atomistic approach to predict the Wulff-Kaischew equilibrium shape of crystals heterogeneously integrated on a dissimilar material. This method uses both reconstructed surface and interface absolute energies, as determined by density functional theory, to infer the morphology and wetting properties of Volmer-Weber islands over the whole range of accessible chemical potentials. The predicted equilibrium shapes of GaP crystals heterogeneously grown on Si, are found to be in good agreements with experimental observations performed by Transmission Electron Microscopy. Such method provides a tool for optimization of hetero-structured, multifunctional and smart materials and devices.

cond-mat.mtrl-sci↗

arXiv2025

Efficient absolute interface energy calculations for heterostructures: Synergy between localized basis sets and surface passivation techniques

Heterostructures combining diverse physico-chemical properties are increasingly in demand for a wide range of applications in modern science and technology. However, despite their importance in materials science, accurately determining absolute interface energies remains a major challenge. Here, we present a computationally efficient framework for determining interface energies by incorporating a surface passivation technique, demonstrated using pseudo H passivation with a localized basis set method and an explicit chemical potential. This framework is applied to calculate absolute interface energies and analyze the electronic properties of quasi lattice matched and lattice mismatched III and V on Si interfaces, with results compared to conventional reconstructed surface calculations. By combining localized basis sets with surface passivation techniques, this framework allows for accurate estimation of absolute interface energies in heterogeneous material systems. This approach effectively addresses issues associated with surface reconstructions while significantly reducing computational costs within the framework of density functional theory, and moreover offers considerable potential for calculating interface energies across diverse material systems.

cond-mat.mtrl-sci↗

arXiv2025

Computational assessment of non-polar and polar GaP terminations for photoelectrochemical water splitting

With photoelectrochemical water splitting being one of the most promising approaches for clean energy production and storage, the search for efficient photoelectrode materials is greater than ever. Gallium phosphide (GaP) is a well-established semiconductor with suitable band edge positions that has already been successfully employed in photoelectrochemical solar cells. However, to utilize it as efficiently as possible, a proper understanding of its properties when interfaced with water is required, and this is currently lacking. In this work we use ab initio molecular dynamics simulations to study the properties of the aqueous interfaces of various GaP non-polar (110) and polar (001) terminations. We calculate their band alignment with respect to the standard hydrogen electrode potential and investigate their interfacial structural properties. Based on these properties we assess the capability of the various terminations to catalyze the reactions associated with water splitting and propose approaches for improving the performance of GaP for application in PECs.

cond-mat.mtrl-sci↗

arXiv2023

Calculating the Circular Dichroism of Chiral Halide Perovskites: A Tight-Binding Approach

Chiral metal halide perovskites have emerged as promising optoelectronic materials for emission and detection of circular polarized visible light. Despite chirality being realized by adding chiral organic cations or ligands, the chiroptical activity originates from the metal halide framework. The mechanism is not well understood, as an overarching modeling framework is lacking. Capturing chirality requires going beyond electric dipole transitions, the common approximation in condensed matter calculations. We present a density functional theory (DFT) parameterized tight-binding (TB) model, which allows us to calculate optical properties including circular dichroism (CD) at low computational cost. Comparing Pb-based chiral perovskites with different organic cations and halide anions, we find that the structural helicity within the metal halide layers determines the size of the CD. Our results mark an important step in understanding the complex correlations of structural, electronic and optical properties of chiral perovskites, and provide a useful tool to predict new compounds with desired properties for novel optoelectronic applications.

cond-mat.mtrl-sci↗

arXiv2020

Tuning the Electronic Levels of NiO with Alkali Halides Surface Modifiers for Perovskite Solar Cells

Favorable optoelectronic properties and ease of fabrication make NiO a promising hole transport layer for perovskite solar cells. To achieve maximum efficiency, the electronic levels of NiO need to be optimally aligned with those of the perovskite absorber. Applying surface modifiers by adsorbing species on the NiO surface, is one of the most widespread strategies to tune its energy levels. Alkali halides are simple inorganic surface modifiers that have been extensively used in organic optoelectronics, however, rarely studied in perovskite solar cells. Using density functional theory (DFT) calculations, we investigate the effect of single layer adsorption of twenty different alkali halides on the electronic levels of NiO. Our results show that alkali halides can shift the position of the valence band maximum (VBM) of NiO to a surprisingly large extend in both directions, from -3:10 eV to +1:59 eV. We interpret the direction and magnitude of the shift in terms of the surface dipoles, formed by the adsorbed cations and anions, where the magnitude of the VBM shift is a monotonic function of the surface coverage. Our results indicate that with alkali halide surface modifiers, the electronic levels of NiO can be tuned robustly and potentially match those of many perovskite compositions in perovskite solar cells.

cond-mat.mtrl-sci↗