Bandgap engineering of compound semiconductors and the fabrication of bandgap-modulated heterostructures are important for enabling the development of modern optoelectronics. However, these engineering processes are challenging for two-dimensional (2D) semiconductors of transition metal dichalcogenides, particularly on a large scale. Herein, we report the wafer-scale homogeneous growth of composition-modulated WS_2xSe_2(1-x) alloys with a continuously tunable bandgap using metal–organic chemical vapor deposition. Well-optimized growth produces monolayer films with excellent homogeneity over the entire wafer. The substitutional atomic chalcogen (S, Se) concentration in WS_2xSe_2(1-x) alloys is precisely controlled by varying the flow rate of the metal–organic precursors, leading to a bandgap modulation from 1.67 to 2.05 eV, as determined from absorbance spectra. Notably, the optical bandgap of WS_2xSe_2(1-x) alloys exhibits a nearly linear relationship with the chalcogen composition, implying a low bowing effect. This bowing-alleviated bandgap modulation is attributed to the small lattice mismatch, strain relaxation, and thermodynamic miscibility in the WS_2xSe_2(1-x) alloys, as confirmed by density-functional theory calculations. Furthermore, the fabrication of hetero-multilayers by stacking differently alloyed films is demonstrated. The produced heterostructure film exhibits a broad spectral absorbance distinct from that of the individual layers. The findings of this study provide insights for the advancement of versatile design of functional 2D optoelectronics.

Quantum wells (QWs), enabling effective exciton confinement and strong light-matter interaction, form an essential building block for quantum optoelectronics. For two-dimensional (2D) semiconductors, however, constructing the QWs is still challenging because suitable materials and fabrication techniques are lacking for bandgap engineering and indirect bandgap transitions occur at the multilayer. Here, we demonstrate an unexplored approach to fabricate atomic–layer–confined multiple QWs (MQWs) via monolithic bandgap engineering of transition metal dichalcogenides and van der Waals stacking. The WO_X/WSe₂ hetero-bilayer formed by monolithic oxidation of the WSe₂ bilayer exhibited the type I band alignment, facilitating as a building block for MQWs. A superlinear enhancement of photoluminescence with increasing the number of QWs was achieved. Furthermore, quantum-confined radiative recombination in MQWs was verified by a large exciton binding energy of 193 meV and a short exciton lifetime of 170 ps. This work paves the way toward monolithic integration of band-engineered heterostructures for 2D quantum optoelectronics.

A gate stack that facilitates a high‐quality interface and tight electrostatic control is crucial for realizing high‐performance and low‐power field‐effect transistors (FETs). However, when constructing conventional metal‐oxide‐semiconductor structures with two‐dimensional (2D) transition metal dichalcogenide channels, achieving these requirements becomes challenging due to inherent difficulties in obtaining high‐quality gate dielectrics through native oxidation or film deposition. Here, a gate‐dielectric‐less device architecture of van der Waals Schottky gated metal–semiconductor FETs (vdW‐SG MESFETs) using a molybdenum disulfide (MoS₂) channel and surface‐oxidized metal gates such as nickel and copper is reported. Benefiting from the strong SG coupling, these MESFETs operate at remarkably low gate voltages, <0.5 V. Notably, they also exhibit Boltzmann‐limited switching behavior featured by a subthreshold swing of ≈60 mV dec⁻¹ and negligible hysteresis. These ideal FET characteristics are attributed to the formation of a Fermi‐level (E_F) pinning‐free gate stack at the Schottky–Mott limit. Furthermore, authors experimentally and theoretically confirm that E_F depinning can be achieved by suppressing both metal‐induced and disorder‐induced gap states at the interface between the monolithic‐oxide‐gapped metal gate and the MoS₂ channel. This work paves a new route for designing high‐performance and energy‐efficient 2D electronics.

Two‐dimensional (2D) materials have emerged as promising candidates for next‐generation electronic and optoelectronic devices owing to their atomically thin nature and inherent immunity to short‐channel effects. However, the integration of high‐quality gate dielectrics has remained a major challenge for most 2D semiconductors, primarily because of their inert, dangling‐bond‐free surfaces, and the absence of stable native oxides. By contrast, bismuth oxyselenide (Bi ₂ O ₂ Se) combines high carrier mobility with the ability to form a thermodynamically stable native oxide possessing a high dielectric constant ( κ ). These properties enable the realization of low‐defect, high‐ κ gate stacks, and have led to remarkable progress in the fabrication of Bi ₂ O ₂ Se‐based field‐effect transistors (FETs). This review highlights recent advancements in the synthesis of Bi ₂ O ₂ Se, with a particular focus on chemical vapor deposition (CVD) as a scalable and industry‐compatible growth method. This article also highlights the various Bi ₂ O ₂ Se growth modes, such as in‐plane, inclined, and vertical orientations. Additionally, the article discusses the evolution of Bi ₂ O ₂ Se FET architectures from planar to fin FET (FinFET)and gate‐all‐around (GAA) configurations. Recent discoveries of ferroelectricity in Bi ₂ O ₂ Se are also introduced for future energy‐efficient electronics, enabling logic‐in‐memory and neuromorphic computing applications through ferroelectric‐semiconductor FETs (FeS‐FETs). Finally, the opportunities and perspectives associated with the incorporation of Bi ₂ O ₂ Se into future low‐power and high‐density logic applications are discussed.