Journal of Semiconductors

Since the invention of amorphous indium–gallium–zinc–oxide (IGZO) based thin-film transistors (TFTs) by Hideo Hosono in 2004, investigations on the topic of IGZO TFTs have been rapidly expanded thanks to their high electrical performance, large-area uniformity, and low processing temperature. This article reviews the recent progress and major trends in the field of IGZO-based TFTs. After a brief introduction of the history of IGZO and the main advantages of IGZO-based TFTs, an overview of IGZO materials and IGZO-based TFTs is given. In this part, IGZO material electron travelling orbitals and deposition methods are introduced, and the specific device structures and electrical performance are also presented. Afterwards, the recent advances of IGZO-based TFT applications are summarized, including flat panel display drivers, novel sensors, and emerging neuromorphic systems. In particular, the realization of flexible electronic systems is discussed. The last part of this review consists of the conclusions and gives an outlook over the field with a prediction for the future.

Solar water splitting is a promising strategy for sustainable production of renewable hydrogen, and solving the crisis of energy and environment in the world. However, large-scale application of this method is hampered by the efficiency and the expense of the solar water splitting systems. Searching for non-toxic, low-cost, efficient and stable photocatalysts is an important way for solar water splitting. Due to the simplicity of structure and the flexibility of composition, perovskite based photocatalysts have recently attracted widespread attention for application in solar water splitting. In this review, the recent developments of perovskite based photocatalysts for water splitting are summarized. An introduction including the structures and properties of perovskite materials, and the fundamentals of solar water splitting is first provided. Then, it specifically focuses on the strategies for designing and modulating perovskite materials to improve their photocatalytic performance for solar water splitting. The current challenges and perspectives of perovskite materials in solar water splitting are also reviewed. The aim of this review is to summarize recent findings and developments of perovskite based photocatalysts and provide some useful guidance for the future research on the design and development of highly efficient perovskite based photocatalysts and the relevant systems for water splitting.

The heterogeneous integration of III–V devices with Si-CMOS on a common Si platform has shown great promise in the new generations of electrical and optical systems for novel applications, such as HEMT or LED with integrated control circuitry. For heterogeneous integration, direct wafer bonding (DWB) techniques can overcome the materials and thermal mismatch issues by directly bonding dissimilar materials systems and device structures together. In addition, DWB can perform at wafer-level, which eases the requirements for integration alignment and increases the scalability for volume production. In this paper, a brief review of the different bonding technologies is discussed. After that, three main DWB techniques of single-, double- and multi-bonding are presented with the demonstrations of various heterogeneous integration applications. Meanwhile, the integration challenges, such as micro-defects, surface roughness and bonding yield are discussed in detail.

Beta gallium oxide (β-Ga₂O₃) has attracted significant attention for applications in power electronics due to its ultra-wide bandgap of ~ 4.8 eV and the large critical electric field of 8 MV/cm. These properties yield a high Baliga's figures of merit (BFOM) of more than 3000. Though β-Ga₂O₃ possesses superior material properties, the lack of p-type doping is the main obstacle that hinders the development of β-Ga₂O₃-based power devices for commercial use. Constructing heterojunctions by employing other p-type materials has been proven to be a feasible solution to this issue. Nickel oxide (NiO) is the most promising candidate due to its wide band gap of 3.6–4.0 eV. So far, remarkable progress has been made in NiO/β-Ga₂O₃ heterojunction power devices. This review aims to summarize recent advances in the construction, characterization, and device performance of the NiO/β-Ga₂O₃ heterojunction power devices. The crystallinity, band structure, and carrier transport property of the sputtered NiO/β-Ga₂O₃ heterojunctions are discussed. Various device architectures, including the NiO/β-Ga₂O₃ heterojunction pn diodes (HJDs), junction barrier Schottky (JBS) diodes, and junction field effect transistors (JFET), as well as the edge terminations and super-junctions based on the NiO/β-Ga₂O₃ heterojunction, are described.

Artificial intelligence (AI) processes data-centric applications with minimal effort. However, it poses new challenges to system design in terms of computational speed and energy efficiency. The traditional von Neumann architecture cannot meet the requirements of heavily data-centric applications due to the separation of computation and storage. The emergence of computing in-memory (CIM) is significant in circumventing the von Neumann bottleneck. A commercialized memory architecture, static random-access memory (SRAM), is fast and robust, consumes less power, and is compatible with state-of-the-art technology. This study investigates the research progress of SRAM-based CIM technology in three levels: circuit, function, and application. It also outlines the problems, challenges, and prospects of SRAM-based CIM macros.

The rapid advancement of information technology has heightened interest in complementary devices and circuits. Conventional p-type semiconductors often lack sufficient electrical performance, thus prompting the search for new materials with high hole mobility and long-term stability. Elemental tellurium (Te), featuring a one-dimensional chiral atomic structure, has emerged as a promising candidate due to its narrow bandgap, high hole mobility, and versatility in industrial applications, particularly in electronics and renewable energy. This review highlights recent progress in Te nanostructures and related devices, focusing on synthesis methods, including vapor deposition and hydrothermal synthesis, which produce Te nanowires, nanorods, and other nanostructures. Critical applications in photodetectors, gas sensors, and energy harvesting devices are discussed, with a special emphasis on their role within the internet of things (IoT) framework, a rapidly growing field that is reshaping our technological landscape. The prospects and potential applications of Te-based technologies are also highlighted.

Halide perovskites have emerged as the next generation of optoelectronic materials and their remarkable performances have been attractive in the fields of solar cells, light-emitting diodes, photodetectors, etc. In addition, halide perovskites have been reported as an attractive new class of X-ray direct detecting materials recently, owning to the strong X-ray stopping capacity, excellent carrier transport, high sensitivity, and cost-effective manufacturing. Meanwhile, perovskite based direct X-ray imagers have been successfully demonstrated as well. In this review article, we firstly introduced some fundamental principles of direct X-ray detection and imaging, and summarized the advances of perovskite materials for these purposes and finally put forward some needful and feasible directions.

Conventional frame-based image sensors suffer greatly from high energy consumption and latency. Mimicking neurobiological structures and functionalities of the retina provides a promising way to build a neuromorphic vision sensor with highly efficient image processing. In this review article, we will start with a brief introduction to explain the working mechanism and the challenges of conventional frame-based image sensors, and introduce the structure and functions of biological retina. In the main section, we will overview recent developments in neuromorphic vision sensors, including the silicon retina based on conventional Si CMOS digital technologies, and the neuromorphic vision sensors with the implementation of emerging devices. Finally, we will provide a brief outline of the prospects and outlook for the development of this field.

The finding of the robust ferroelectricity in HfO₂-based thin films is fantastic from the view point of both the fundamentals and the applications. In this review article, the current research status of the future prospects for the ferroelectric HfO₂-based thin films and devices are presented from fundamentals to applications. The related issues are discussed, which include: 1) The ferroelectric characteristics observed in HfO₂-based films and devices associated with the factors of dopant, strain, interface, thickness, defect, fabrication condition, and more; 2) physical understanding on the observed ferroelectric behaviors by the density functional theory (DFT)-based theory calculations; 3) the characterizations of microscopic and macroscopic features by transmission electron microscopes-based and electrical properties-based techniques; 4) modeling and simulations, 5) the performance optimizations, and 6) the applications of some ferroelectric-based devices such as ferroelectric random access memory, ferroelectric-based field effect transistors, and the ferroelectric tunnel junction for the novel information processing systems.

Lead chalcohalides (PbYX, X = Cl, Br, I; Y = S, Se) is an extension of the classic Pb chalcogenides (PbY). Constructing the heterogeneous integration with PbYX and PbY material systems makes it possible to achieve significantly improved optoelectronic performance. In this work, we studied the effect of introducing halogen precursors on the structure of classical PbS nanocrystals (NCs) during the synthesis process and realized the preparation of PbS/Pb₃S₂X₂ core/shell structure for the first time. The core/shell structure can effectively improve their optical properties. Furthermore, our approach enables the synthesis of Pb₃S₂Br₂ that had not yet been reported. Our results not only provide valuable insights into the heterogeneous integration of PbYX and PbY materials to elevate material properties but also provide an effective method for further expanding the preparation of PbYX material systems.

In this work, we studied the persistent photoconductivity (PPC) spectra in single HgTe/CdHgTe quantum wells with different growth parameters and different types of dark conductivity. The studies were performed in a wide radiation quantum energy range of 0.62–3.1 eV both at T = 4.2 K and at T = 77 K. Common features of the PPC spectra for all structures were revealed, and their relation to the presence of a CdTe cap layer in all structures and the appropriate cadmium fraction in the CdHgTe barrier layers was shown. One of the features was associated with the presence of a deep level in the CdTe layer. In addition, the oscillatory behavior of the PPC spectra in the region from 0.8–1.1 eV to 1.2–1.5 eV was observed. It is associated with the cascade emission of longitudinal optical phonons in CdHgTe barrier.

In order to address challenges posed by the reduction in transistor size, researchers are concentrating on two-dimensional (2D) materials with high dielectric constants and large band gaps. Monoclinic ZrO₂ (m-ZrO₂) has emerged as a promising gate dielectric material due to its suitable dielectric constant, wide band gap, ideal valence-band offset, and good thermodynamic stability. However, current deposition methods face compatibility issues with 2D semiconductors, highlighting the need for high-quality dielectrics and interfaces. Here, high-quality 2D m-ZrO₂ single crystals are successfully prepared using a one-step chemical vapor deposition (CVD) method, aided by 5A molecular sieves for oxygen supply. The prepared ZrO₂ is utilized as a gate dielectric in the construction of MoS₂ field-effect transistors (FETs) to investigate its electrical property. The FETs exhibit a high carrier mobility of up to 5.50 cm²·V⁻¹·s⁻¹, and a current switching ratio (I_on/off) of approximately 10⁴, which aligns with the current standards of logic circuits, indicating that ZrO₂ has application value as a gate dielectric. The successful one-step preparation of single-crystal ZrO₂ paves the way for the utilization of high-κ gate dielectrics and creates favorable conditions for the development of high-performance semiconductor devices, offering new possibilities for transistor miniaturization.

Semiconductor colloidal quantum wells (CQWs) with atomic-precision layer thickness are rapidly gaining attention for next-generation optoelectronic applications due to their tunable optical and electronic properties. In this study, we investigate the dielectric and optical characteristics of CdSe CQWs with monolayer numbers ranging from 2 to 7, synthesized via thermal injection and atomic layer (c-ALD) deposition techniques. Through a combination of spectroscopic ellipsometry (SE) and first-principles calculations, we demonstrate the significant tunability of the bandgap, refractive index, and extinction coefficient, driven by quantum confinement effects. Our results show a decrease in bandgap from 3.1 to 2.0 eV as the layer thickness increases. Furthermore, by employing a detailed analysis of the absorption spectra, accounting for exciton localization and asymmetric broadening, we precisely capture the relationship between monolayer number and exciton binding energy. These findings offer crucial insights for optimizing CdSe CQWs in optoelectronic device design by leveraging their layer-dependent properties.

Colloidal quantum dots (CQDs) are highly regarded for their outstanding photovoltaic characteristics, including excellent color purity, stability, high photoluminescence quantum yield (PLQY), narrow emission spectra, and ease of solution processing. Despite significant progress in quantum dot light-emitting diodes (QLEDs) technology since its inception in 1994, blue QLEDs still fall short in efficiency and lifespan compared to red and green versions. The toxicity concerns associated with Cd/Pb-based quantum dots (QDs) have spurred the development of heavy-metal-free alternatives, such as group Ⅱ−Ⅵ (e.g., ZnSe-based QDs), group Ⅲ−Ⅴ (e.g., InP, GaN QDs), and carbon dots (CDs). In this review, we discuss the key properties and development history of quantum dots (QDs), various synthesis approaches, the role of surface ligands, and important considerations in developing core/shell (C/S) structured QDs. Additionally, we provide an outlook on the challenges and future directions for blue QLEDs.

Perovskite materials have emerged as promising candidates for various optoelectronic applications owing to their remarkable optoelectronic properties and easy solution processing. Metal halide perovskites, as direct-bandgap semiconductors, show an excellent class of optical gain media, which makes them applicable to the development of low-threshold or even thresholdless lasers. This mini review explores recent advances in perovskite-based laser technology, which have led to chiral single-mode microlasers, low-threshold, external-cavity-free lasing devices at room temperature, and other innovative device architectures. Including self-assembled CsPbBr₃ microwires that enable edge lasing. Realized continuous-wave (CW) pumped lasing by perovskite material pushes the research of electrically driven perovskite lasers. The capacity to regulate charge transport in halide perovskites further enhances their applicability in optoelectronic systems. The ongoing integration of perovskite materials with advanced photonic structures holds excellent potential for future innovations in laser technology and photovoltaics. We also highlight the transformative potential of perovskite materials in advancing the next generation of efficient and integrated optoelectronic devices.

Optical network-on-chip (ONoC) systems have emerged as a promising solution to overcome limitations of traditional electronic interconnects. Efficient ONoC architectures rely on optical routers, enabling high-speed data transfer, efficient routing, and scalability. This paper presents a comprehensive survey analyzing optical router designs, specifically microring resonators (MRRs), Mach−Zehnder interferometers (MZIs), and hybrid architectures. Selected comparison criteria, chosen for their critical importance, significantly impact router functionality and performance. By emphasizing these criteria, valuable insights into the strengths and limitations of different designs are gained, facilitating informed decisions and advancements in optical networking. While other factors contribute to performance and efficiency, the chosen criteria consistently address fundamental elements, enabling meaningful evaluation. This work serves as a valuable resource for beginners, providing a solid foundation in understanding ONoC and optical routers. It also offers an in-depth survey for experts, laying the groundwork for further exploration. Additionally, the importance of considering design constraints and requirements when selecting an optimal router design is highlighted. Continued research and innovation will enable the development of efficient optical router solutions that meet the evolving needs of modern computing systems. This survey underscores the significance of ongoing advancements in the field and their potential impact on future technologies.

Flexible photodetectors have garnered significant attention by virtue of their potential applications in environmental monitoring, wearable healthcare, imaging sensing, and portable optical communications. Perovskites stand out as particularly promising materials for photodetectors, offering exceptional optoelectronic properties, tunable band gaps, low-temperature solution processing, and notable mechanical flexibility. In this review, we explore the latest progress in flexible perovskite photodetectors, emphasizing the strategies developed for photoactive materials and device structures to enhance optoelectronic performance and stability. Additionally, we discuss typical applications of these devices and offer insights into future directions and potential applications.

Heart rate variability (HRV) that can reflect the dynamic balance between the sympathetic nervous and parasympathetic nervous of human autonomic nervous system (ANS) has attracted considerable attention. However, traditional electrocardiogram (ECG) devices for HRV analysis are bulky, and hard wires are needed to attach measuring electrodes to the chest, resulting in the poor wearable experience during the long-term measurement. Compared with that, wearable electronics enabling continuously cardiac signals monitoring and HRV assessment provide a desirable and promising approach for helping subjects determine sleeping issues, cardiovascular diseases, or other threats to physical and mental well-being. Until now, significant progress and advances have been achieved in wearable electronics for HRV monitoring and applications for predicting human physical and mental well-being. In this review, the latest progress in the integration of wearable electronics and HRV analysis as well as practical applications in assessment of human physical and mental health are included. The commonly used methods and physiological signals for HRV analysis are briefly summarized. Furthermore, we highlighted the research on wearable electronics concerning HRV assessment and diverse applications such as stress estimation, drowsiness detection, etc. Lastly, the current limitations of the integrated wearable HRV system are concluded, and possible solutions in such a research direction are outlined.

With the rapid development of artificial intelligence (AI) technology, the demand for high-performance and energy-efficient computing is increasingly growing. The limitations of the traditional von Neumann computing architecture have prompted researchers to explore neuromorphic computing as a solution. Neuromorphic computing mimics the working principles of the human brain, characterized by high efficiency, low energy consumption, and strong fault tolerance, providing a hardware foundation for the development of new generation AI technology. Artificial neurons and synapses are the two core components of neuromorphic computing systems. Artificial perception is a crucial aspect of neuromorphic computing, where artificial sensory neurons play an irreplaceable role thus becoming a frontier and hot topic of research. This work reviews recent advances in artificial sensory neurons and their applications. First, biological sensory neurons are briefly described. Then, different types of artificial neurons, such as transistor neurons and memristive neurons, are discussed in detail, focusing on their device structures and working mechanisms. Next, the research progress of artificial sensory neurons and their applications in artificial perception systems is systematically elaborated, covering various sensory types, including vision, touch, hearing, taste, and smell. Finally, challenges faced by artificial sensory neurons at both device and system levels are summarized.