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The recent development of three‐dimensional semiconductor integration technology demands a key component—the ovonic threshold switching (OTS) selector to suppress the current leakage in the high‐density memory chips. Yet, the unsatisfactory performance of existing OTS materials becomes the bottleneck of the industrial advancement. The sluggish development of OTS materials, which are usually made from chalcogenide glass, should be largely attributed to the insufficient understanding of the electronic structure in these materials, despite of intensive research in the past decade. Due to the heavy first‐principles computation on disordered systems, a universal theory to explain the origin of mid‐gap states (MGS), which are the key feature leading to the OTS behavior, is still lacking. To avoid the formidable computational tasks, we adopt machine learning method to understand and predict MGS in typical OTS materials. We build hundreds of chalcogenide glass models and collect major structural features from both short‐range order (SRO) and medium‐range order (MRO) of the amorphous cells. After training the artificial neural network using these features, the accuracy has reached ~95% when it recognizes MGS in new glass. By analyzing the synaptic weights of the input structural features, we discover that the bonding and coordination environments from SRO and particularly MRO are closely related to MGS. The trained model could be used in many other OTS chalcogenides after minor modification. The intelligent machine learning allows us to understand the OTS mechanism from vast amount of structural data without heavy computational tasks, providing a new strategy to design functional amorphous materials from first principles. The 3D semiconductor fabrication technology requires an “ovonic threshold switching (OTS)” selector device to control the open and shut of each memory unit. The physics of these materials, however, has not been well understood due to complex structure of chalcogenide glass. The authors focus on the defect states which are responsible for OTS behaviors via machine learning of the large amount of structure data. The physical origin of OTS is revealed and the properties of these materials can be predicted, paving the way for the materials design toward high‐density memory integration.

Defect engineering is an innovative approach that greatly enhances the performance of photocatalysts, especially in water‐splitting applications for sustainable green energy. This method involves introducing structural imperfections, such as lattice vacancies or foreign atom substitutions, to improve the photocatalytic properties of semiconductors. These defects can alter critical aspects of photocatalytic reactions by adjusting the band structure and increasing light absorption. For instance, anionic vacancies introduce mid‐gap states that broaden light absorption, while cationic vacancies lower the bandgap without forming such states. When both vacancy types are present simultaneously, they create a p–n homojunction, facilitating charge carrier separation through its distinct built‐in electric field. Defects are typically categorized as either surface defects or bulk defects. Surface defects improve charge carrier mobility, promote reactant adsorption, and initiate photocatalytic reactions, while bulk defects frequently serve as recombination centers. In addition, the level of these defects is critical; keeping them at an optimal balance can significantly improve photocatalytic efficiency, but excessive defects may lead to increased recombination, which reduces efficiency. Achieving the right balance in defect type, distribution, and concentration is key to optimizing photocatalytic performance, underscoring the essential role of defect engineering in advancing green energy solutions. By creating anion and cation vacancies, scientists fine‐tune semiconductor bandgaps and extend light absorption, boosting charge separation in photocatalysts. Surface defects enhance reactant adsorption and carrier transport, while controlled bulk defects curb recombination. Precise defect type, location, and concentration balance is crucial for efficient solar water splitting.

TiO 2 /BiVO 4 heterojunctions are considered to be one of the most promising materials for photocatalysts due to their extended carrier lifetime, high visible light response, and good stability. However, while Type-II TiO 2 /BiVO 4 heterojunctions are well-studied, the fundamental mechanism behind the Type-I configurations remains unclear, particularly regarding their unexpected high photocatalytic activity despite theoretically unfavorable band alignment. Herein, we reveal that localized polaronic mid-gap states (SP states) can mediate efficient charge transfer and recombination in TiO 2 /BiVO 4 using time-resolved photoluminescence (PL) spectroscopy and transient absorption spectroscopy (TAS), providing direct experimental evidence of this mechanism. The existence of SP states enables exceptional methyl orange degradation efficiency (nearly 100% in 1 h under visible light) despite the theoretically unfavorable Type-I alignment. This work redefines the potential of Type-I systems for visible-light photocatalysis by demonstrating how polaron engineering overcomes the limitations of traditional band structures, advancing their applications in solar utilization.

A photodetector capable of detecting light illuminations ranging from ultraviolet (UV) to visible light spectrum using earth-abundant and environmentally friendly Cu-doped zinc tin oxide (Cu-doped ZTO) thin films is reported. Trilayer photodetector devices comprising P+-Si/10 at.% Cu-doped-ZTO-thin-film/indium-tin-oxide were successfully fabricated using radio-frequency (RF) magnetron sputtering. Optical and photoconductive characteristics of trilayer photodetector devices were investigated. The devices were found to exhibit superior photodetection capabilities, including high sensitivities of 1147 and 758, under 630-nm and 352-nm light illumination, respectively, and corresponding fast photoresponse times with a rise-time/fall-time of 8.9 ms/8.0 ms and 8.8 ms/8.0 ms. The induced mid-gap states from the Cu-dopant contributed extensively to the photoresponse through stable optical transitions. Air-annealing the Cu-ZTO thin films at 600°C effectively reduced the dark current, enabling Cu-ZTO thin films suitable for UV–visible light, wide spectral photodetector applications.

We report a theoretical study of dielectric properties of models of amorphous Boron Nitride, using interatomic potentials generated by machine learning. We first perform first-principles simulations on small (about 100 atoms in the periodic cell) sample sizes to explore the emergence of mid-gap states and its correlation with structural features. Next, by using a simplified tight-binding electronic model, we analyse the dielectric functions for complex three dimensional models (containing about 10.000 atoms) embedding varying concentrations of sp 1 , sp 2 and sp 3 bonds between B and N atoms. Within the limits of these methodologies, the resulting value of the zero-frequency dielectric constant is shown to be influenced by the population density of such mid-gap states and their localization characteristics. We observe nontrivial correlations between the structure-induced electronic fluctuations and the resulting dielectric constant values. Our findings are however just a first step in the quest of accessing fully accurate dielectric properties of as-grown amorphous BN of relevance for interconnect technologies and beyond.

In this work, we report a hybrid architecture of layered MoS2/graphene synthesized by an ultrasonic-assisted hydrothermal method at 230°C with a reaction time of 2 h. The microstructure, morphology, chemical composition and optical properties of MoS2/graphene were analyzed by x-ray diffraction, field emission scanning electron microscope (FESEM), high resolution transmission electron microscope (HRTEM), Raman spectroscopy, hard x-ray photoelectron spectroscopy (HAXPES), energy dispersive x-ray (EDX) spectroscopy and photoluminescence measurements. The FESEM results show that the ultrathin MoS2 nanosheets directly deposited on the surfaces of graphene sheets with high density and uniform shape. The TEM and HRTEM images indicate that MoS2 nanosheets with average thickness of ∼ 3–6 nm (6–8 layers) grow vertically on the graphene surface, forming three-dimensional MoS2/graphene hybrid structures. Both XRD and Raman analyses elucidate that the as-grown MoS2 phase of MoS2/graphene composite crystalized in a hexagonal phase (2H-MoS2) with low impurity, which was later confirmed by the HAXPES and EDX. Interestingly, the D-band in the Raman spectrum of MoS2/graphene hybrid samples almost disappears as the 2D-band arises, revealing that defects in the graphene oxide are well repaired under the hydrothermal process. Furthermore, the as-synthesized MoS2/graphene exhibits strong photoluminescence with separately resolved emission peaks in the visible range (∼ 1.75–1.78 eV, ∼ 1.89–1.93 eV and ∼ 1.99–2.05 ,eV) which is a signature of mid-gap states in their optical bandgap compare to that of as-synthesized MoS2. Our synthesis approach is favorable for easy and low-cost preparation of MoS2/graphene composite, rendering the material attractive for various optoelectronic and catalysis applications.

Cadmium chalcogenide semiconductor quantum dots, especially doped nanoclusters, have attracted great attention for their effects on photo generated carriers and their lifetime due to introduced trapping states by changing surface unbonded orbitals. Here, we investigate the adsorption of Ag on “magic-sized” cadmium chalcogenide (CdTe) 13 core-cage nanoclusters, Cd 13 Te 13 Ag, by first-principles density functional theory. All possible adsorption sites, top, bridge, and hollow sites, have been considered. Particular attention is paid to the energy band structures of Cd 13 Te 13 Ag. The study demonstrates that the hollow sites, the centers of hexagons, are the favorite Ag adsorption sites. Unlike observed shallow acceptor level of doped QDs, two unusual deep mid-gap states with different spins, spin up and spin down, are observed. These two deep states shift with Ag moving towards the core of cage. The detail properties of adsorption configurations and these two deep states are analyzed. These two deep states should have important role to their optical applications.

The two-dimensional (2D) materials-based tunneling field-effect transistors (TFETs) suffer from low driving currents. In contrast to the prevailing wisdom that defects are detrimental, we proposed to harness the ubiquitous defects in MoS2 to overcome the problem of the low on-state current in TFET. The existence of certain molybdenum-related vacancies and sulfur vacancy in appropriate positions confers the higher driving currents without compromising the low-power benefits. Such performance enhancements are related to the defect-assisted resonant Zener tunneling mechanism introduced by the mid-gap states of the vacancy defects. These unveiled hidden defect benefits could provide new opportunities for boosting the performance of 2D TFETs.

The two-dimensional (2D) materials-based tunneling field-effect transistors (TFETs) suffer from low driving currents. In contrast to the prevailing wisdom that defects are detrimental, we proposed to harness the ubiquitous defects in MoS 2 to overcome the problem of the low on-state current in TFET. The existence of certain molybdenum-related vacancies and sulfur vacancy in appropriate positions confers the higher driving currents without compromising the low-power benefits. Such performance enhancements are related to the defect-assisted resonant Zener tunneling mechanism introduced by the mid-gap states of the vacancy defects. These unveiled hidden defect benefits could provide new opportunities for boosting the performance of 2D TFETs. The defect-assisted resonant Zener tunneling mechanism in TFET introduced by the mid-gap states of the vacancies in MoS 2 is beneficial for enhancing the on-state current.

This chapter contains sections titled: Introduction Electromagnetic Radiation Refractive Index Interaction of EM Radiation with Organic Molecules Transmission and Reflection from Interfaces Waveguiding Surface Plasmons Photonic Crystals Bibliography References