Ambipolar Channel p-TMD/n-Ga2 O3 Junction Field Effect Transistors and High Speed Photo-sensing in TMD Channel

J-MISFET Hybrid Dual-Gate Switching Device for Multifunctional Optoelectronic Logic Gate Applications

High-performance and low operating voltage are becoming increasingly significant device parameters to meet the needs of future integrated circuit (IC) processors and ensure their energy-efficient use in upcoming mobile devices. In this study, we suggest a hybrid dual-gate switching device consisting of the vertically stacked junction and metal-insulator-semiconductor (MIS) gate structure, named J-MISFET. It shows excellent device performances of low operating voltage (<0.5 V), drain current ON/OFF ratio (∼4.7 × 105), negligible hysteresis window (<0.5 mV), and near-ideal subthreshold slope (SS) (60 mV/dec), making it suitable for low-power switching operation. Furthermore, we investigated the switchable NAND/NOR logic gate operations and the photoresponse characteristics of the J-MISFET under the small supply voltage (0.5 V). To advance the applications further, we successfully demonstrated an integrated optoelectronic security logic system comprising 2-electric inputs (for encrypted data) and 1-photonic input signal (for password key) as a hardware security device for data protection. Thus, we believe that our J-MISFET, with its heterogeneous hybrid gate structures, will illuminate the path toward future device configurations for next-generation low-power electronics and multifunctional security logic systems in a data-driven society.

Structural and surface characterizations of 2D β-In2Se3/3D β-Ga2O3 heterostructures grown on c-Sapphire substrates by molecular beam epitaxy

Integrating two-dimensional (2D) layered materials with wide bandgap β-Ga2O3 has unveiled impressive opportunities for exploring novel physics and device concepts. This study presents the epitaxial growth of 2D β-In2Se3/3D β-Ga2O3 heterostructures on c-Sapphire substrates by plasma-assisted molecular beam epitaxy. Firstly, we employed a temperature-dependent two-step growth process to deposit Ga2O3 and obtained a phase-pure ( 2 ¯ 01 ) β-Ga2O3 film on c-Sapphire. Interestingly, the in-situ reflective high-energy electron diffraction (RHEED) patterns observed from this heterostructure revealed the in-plane 'b' lattice constant of β-Ga2O3 ~ 3.038Å. In the next stage, for the first time, 2D In2Se3 layers were epitaxially realized on 3D β-Ga2O3 under varying substrate temperatures (Tsub) and Se/In flux ratios (RVI/III). The deposited layers exhibited (00l) oriented β-In2Se3 on ( 2 ¯ 01 ) β-Ga2O3/c-Sapphire with the epitaxial relationship of [ 11 2 ¯ 0 ] β-In2Se3 || [010] β-Ga2O3 and [ 10 1 ¯ 0 ] β-In2Se3 || [102] β-Ga2O3 as observed from the RHEED patterns. Also, the in-plane 'a' lattice constant of β-In2Se3 was determined to be ~ 4.027Å. The single-phase β-In2Se3 layers with improved structural and surface quality were achieved at a Tsub ~ 280 °C and RVI/III ~ 18. The microstructural and detailed elemental analysis further confirmed the epitaxy of 2D layered β-In2Se3 on 3D β-Ga2O3, a consequence of the quasi-van der Waals epitaxy. Furthermore, the β-Ga2O3 with an optical bandgap (Eg) of ~ 5.04 eV (deep ultraviolet) when integrated with 2D β-In2Se3, Eg ~ 1.43eV (near infra-red) can reveal potential applications in the optoelectronic field.

Progress in Gallium Oxide Field-Effect Transistors for High-Power and RF Applications

Power electronics are becoming increasingly more important, as electrical energy constitutes 40% of the total primary energy usage in the USA and is expected to grow rapidly with the emergence of electric vehicles, renewable energy generation, and energy storage. New materials that are better suited for high-power applications are needed as the Si material limit is reached. Beta-phase gallium oxide (β-Ga2O3) is a promising ultra-wide-bandgap (UWBG) semiconductor for high-power and RF electronics due to its bandgap of 4.9 eV, large theoretical breakdown electric field of 8 MV cm-1, and Baliga figure of merit of 3300, 3-10 times larger than that of SiC and GaN. Moreover, β-Ga2O3 is the only WBG material that can be grown from melt, making large, high-quality, dopable substrates at low costs feasible. Significant efforts in the high-quality epitaxial growth of β-Ga2O3 and β-(AlxGa1-x)2O3 heterostructures has led to high-performance devices for high-power and RF applications. In this report, we provide a comprehensive summary of the progress in β-Ga2O3 field-effect transistors (FETs) including a variety of transistor designs, channel materials, ohmic contact formations and improvements, gate dielectrics, and fabrication processes. Additionally, novel structures proposed through simulations and not yet realized in β-Ga2O3 are presented. Main issues such as defect characterization methods and relevant material preparation, thermal studies and management, and the lack of p-type doping with investigated alternatives are also discussed. Finally, major strategies and outlooks for commercial use will be outlined.

2D Amorphous GaOX Gate Dielectric for β-Ga2O3 Field-Effect Transistors

Appropriate gate dielectrics must be identified to fabricate metal-insulator-semiconductor field-effect transistors (MISFETs); however, this has been challenging for compound semiconductors owing to the absence of high-quality native oxides. This study uses the liquid-gallium squeezing technique to fabricate 2D amorphous gallium oxide (GaOX) with a high dielectric constant, where its thickness is precisely controlled at the atomic scale (monolayer, ∼4.5 nm; bilayer, ∼8.5 nm). Beta-phase gallium oxide (β-Ga2O3) with an ultrawide energy bandgap (4.5-4.9 eV) has emerged as a next-generation power semiconductor material and is presented here as the channel material. The 2D amorphous GaOX dielectric is combined with a β-Ga2O3 conducting nanolayer, and the resulting β-Ga2O3 MISFET is stable up to 250 °C. The 2D amorphous GaOX is oxygen-deficient, and a high-quality interface with excellent uniformity and scalability forms between the 2D amorphous GaOX and β-Ga2O3. The fabricated MISFET exhibits a wide gate-voltage swing of approximately +5 V, a high current on/off ratio, moderate field-effect carrier mobility, and a decent three-terminal breakdown voltage (∼138 V). The carrier transport of the Ni/GaOX/β-Ga2O3 metal-insulator-semiconductor (MIS) structure displays a combination of Schottky emission and Fowler-Nordheim (F-N) tunneling in the high-gate-bias region at 25 °C, whereas at elevated temperatures it shows Schottky emission and F-N tunneling in the low- and high-gate-bias regions, respectively. This study demonstrates that a 2D GaOX gate dielectric layer can be produced and incorporated into an active channel layer to form an MIS structure at room temperature (∼25 °C), which enables the facile fabrication of MISFET devices.

Multifunctional Magnetic Oxide-MoS2 Heterostructures on Silicon

Correlated oxides and related heterostructures are intriguing for developing future multifunctional devices by exploiting their exotic properties, but their integration with other materials, especially on Si-based platforms, is challenging. Here, van der Waals heterostructures of La0.7 Sr0.3 MnO3 (LSMO) , a correlated manganite perovskite, and MoS2 are demonstrated on Si substrates with multiple functions. To overcome the problems due to the incompatible growth process, technologies involving freestanding LSMO membranes and van der Waals force-mediated transfer are used to fabricate the LSMO-MoS2 heterostructures. The LSMO-MoS2 heterostructures exhibit a gate-tunable rectifying behavior, based on which metal-semiconductor field-effect transistors (MESFETs) with on-off ratios of over 104 can be achieved. The LSMO-MoS2 heterostructures can function as photodiodes displaying considerable open-circuit voltages and photocurrents. In addition, the colossal magnetoresistance of LSMO endows the LSMO-MoS2 heterostructures with an electrically tunable magnetoresponse at room temperature. This work not only proves the applicability of the LSMO-MoS2 heterostructure devices on Si-based platform but also demonstrates a paradigm to create multifunctional heterostructures from materials with disparate properties.

Self-Assembled TaOX/2H-TaS2 as a van der Waals Platform of a Multilevel Memristor Circuit Integrated with a β-Ga2O3 Transistor

Two-dimensional (2D)-layered material tantalum disulfide (2H-TaS₂) is known to be a van der Waals conductor at room temperature. Here, 2D-layered TaS₂ has been partially oxidized by utraviolet-ozone (UV-O₃) annealing to form a 12-nm-thin TaO_X on conducting TaS₂, so that the TaO_X/2H-TaS₂ structure might be self-assembled. Utilizing the TaO_X/2H-TaS₂ structure as a platform, each device of a β-Ga₂O₃ channel MOSFET and a TaO_X memristor has been successfully fabricated. An insulator structure of Pt/TaO_X/2H-TaS₂ shows good a dielectric constant (k ∼ 21) and strength (∼3 MV/cm) of achieved TaO_X, which is enough to support a β-Ga₂O₃ transistor channel. Based on the quality of TaO_X and low trap density of the TaO_X/β-Ga₂O₃ interface, which is achieved via another UV-O₃ annealing, excellent device properties such as little hysteresis (<∼0.04 V), band-like transport, and a steep subthreshold swing of ∼85 mV/dec are achieved. With a Cu electrode on top of the TaO_X/2H-TaS₂ structure, the TaO_X acts as a memristor operating around ∼2 V for nonvolatile bipolar and unipolar mode memories. The functionalities of the TaO_X/2H-TaS₂ platform become more distinguished finally when the Cu/TaO_X/2H-TaS₂ memristor and β-Ga₂O₃ MOSFET are integrated to form a resistive memory switching circuit. The circuit nicely demonstrates the multilevel memory functions.

State-of-the-Art β-Ga2O3 Field-Effect Transistors for Power Electronics

Due to the emergence of electric vehicles, power electronics have become the new focal point of research. Compared to commercialized semiconductors, such as Si, GaN, and SiC, power devices based on β-Ga2O3 are capable of handling high voltages in smaller dimensions and with higher efficiencies, because of the ultrawide bandgap (4.9 eV) and large breakdown electric field (8 MV cm-1). Furthermore, the β-Ga2O3 bulk crystals can be synthesized by the relatively low-cost melt growth methods, making the single-crystal substrates and epitaxial layers readily accessible for fabricating high-performance power devices. In this article, we first provide a comprehensive review on the material properties, crystal growth, and deposition methods of β-Ga2O3, and then focus on the state-of-the-art depletion mode, enhancement mode, and nanomembrane field-effect transistors (FETs) based on β-Ga2O3 for high-power switching and high-frequency amplification applications. In the meantime, device-level approaches to cope with the two main issues of β-Ga2O3, namely, the lack of p-type doping and the relatively low thermal conductivity, will be discussed and compared.

Low-Temperature-Crystallized Ga2O3 Thin Films and Their TFT-Type Solar-Blind Photodetectors

Crystalline Ga₂O₃ (c-Ga₂O₃) is a promising candidate for next-generation solar-blind photodetectors (SBPDs) but is suffering from high processing temperatures. Herein, seed-induced engineering is proposed via adopting Zn as an induced metal for crystallizing Ga₂O₃, lowering the processing temperature by 200 °C. After annealing, the Zn/Ga₂O₃ consists of an inner Ga₂O₃ layer of a monoclinic crystalline phase, top ZnO crystals coming from Zn oxidation, and a thin corundum Ga₂O₃ layer between them, which implies a "seed-induced" crystallization mechanism besides the nonequilibrium chaotic state caused by the traditional electron transfer one. As a result, the tailored c-Ga₂O₃ thin-film transistor-type SBPD with enhanced packing density and finite oxygen deficiency demonstrates a satisfactory responsivity of 8.6 A/W and also an ultrahigh UVC/visible rejection ratio (R₂₅₄/R₄₅₀) of 2 × 10⁵. The seed-induced engineering forecasts its potential application in crystalline Ga₂O₃ SBPDs under a relatively low processing temperature.

A Submicrosecond-Response Ultraviolet-Visible-Near-Infrared Broadband Photodetector Based on 2D Tellurosilicate InSiTe3

2D material (2DM) based photodetectors with broadband photoresponse are of great value for a vast number of applications such as multiwavelength photodetection, imaging, and night vision. However, compared with traditional photodetectors based on bulk material, the relatively slow speed performance of 2DM based photodetectors hinders their practical applications. Herein, a submicrosecond-response photodetector based on ternary telluride InSiTe₃ with trigonal symmetry and layered structure was demonstrated in this study. The InSiTe₃ based photodetectors exhibit an ultrafast photoresponse (545-576 ns) and broadband detection capabilities from the ultraviolet (UV) to the near-infrared (NIR) optical communication region (365-1310 nm). Besides, the photodetector presents an outstanding reversible and stable photoresponse in which the response performance remains consistent within 200 000 cycles of switch operation. These significant findings suggest that InSiTe₃ can be a promising candidate for constructing fast response broadband 2DM based optoelectronic devices.

2D Ultrawide Bandgap Semiconductors: Odyssey and Challenges

2D ultrawide bandgap (UWBG) semiconductors have aroused increasing interest in the field of high-power transparent electronic devices, deep-ultraviolet photodetectors, flexible electronic skins, and energy-efficient displays, owing to their intriguing physical properties. Compared with dominant narrow bandgap semiconductor material families, 2D UWBG semiconductors are less investigated but stand out because of their propensity for high optical transparency, tunable electrical conductivity, high mobility, and ultrahigh gate dielectrics. At the current stage of research, the most intensively investigated 2D UWBG semiconductors are metal oxides, metal chalcogenides, metal halides, and metal nitrides. This paper provides an up-to-date review of recent research progress on new 2D UWBG semiconductor materials and novel physical properties. The widespread applications, i.e., transistors, photodetector, touch screen, and inverter are summarized, which employ 2D UWBG semiconductors as either a passive or active layer. Finally, the existing challenges and opportunities of the enticing class of 2D UWBG semiconductors are highlighted.

2D Heterostructures for Ubiquitous Electronics and Optoelectronics: Principles, Opportunities, and Challenges

A grand family of two-dimensional (2D) materials and their heterostructures have been discovered through the extensive experimental and theoretical efforts of chemists, material scientists, physicists, and technologists. These pioneering works contribute to realizing the fundamental platforms to explore and analyze new physical/chemical properties and technological phenomena at the micro-nano-pico scales. Engineering 2D van der Waals (vdW) materials and their heterostructures via chemical and physical methods with a suitable choice of stacking order, thickness, and interlayer interactions enable exotic carrier dynamics, showing potential in high-frequency electronics, broadband optoelectronics, low-power neuromorphic computing, and ubiquitous electronics. This comprehensive review addresses recent advances in terms of representative 2D materials, the general fabrication methods, and characterization techniques and the vital role of the physical parameters affecting the quality of 2D heterostructures. The main emphasis is on 2D heterostructures and 3D-bulk (3D) hybrid systems exhibiting intrinsic quantum mechanical responses in the optical, valley, and topological states. Finally, we discuss the universality of 2D heterostructures with representative applications and trends for future electronics and optoelectronics (FEO) under the challenges and opportunities from physical, nanotechnological, and material synthesis perspectives.

High-Performance Harsh-Environment-Resistant GaOX Solar-Blind Photodetectors via Defect and Doping Engineering

Gallium oxide (Ga₂ O₃ ), with an ultrawide bandgap, is currently regarded as one of the most promising materials for solar-blind photodetectors (SBPDs), which are greatly demanded in harsh environment, such as space exploration and flame prewarning. However, realization of high-performance SBPDs with high tolerance toward harsh environments based on low-cost Ga₂ O₃ material faces great challenges. Here, defect and doping (DD) engineering towards amorphous GaO_X (a-GaO_X ) has been proposed to obtain ultrasensitive SBPDs for harsh condition application. Serious oxygen deficiency and doping compensation of the engineered a-GaO_X film ensure the high response currents and low dark currents, respectively. Annealing item in nitrogen of DD engineering also incurs the recrystallization of material, formation of nanopores by oxygen escape, and suppression of sub-bandgap defect states. As a result, the tailored GaO_X SBPD based on DD engineering not only harvests a record-high responsivity rejection ratio (R_{254 nm} /R_{365 nm} ) of 1.8 × 10⁷ , 10² times higher detectivity, and 2 × 10² times faster decay speed than the control device, but also keeps a high responsivity, high photo-to-dark current ratio, and sharp imaging capability even at high temperature (280 °C) or high bias (100 V). The proposed DD engineering provides an effective strategy towards highly harsh-environment-resistant GaO_X SBPDs.