Atomically thin 2-D semiconductors are widely used to build various novel photodiodes due to their appropriate band structure and dangling-bond-free surface. These emerging 2-D photodiodes have shown excellent performance, especially in responsivity. Here, we report a Schottky metal–semiconductor photodiode with an ultrashort molybdenum disulfide (MoS2) channel constructed by a vertical structure. The device showed excellent rectification and optical response characteristics due to the large Schottky barrier height ( $\text{q}\varphi _{\text{SB}}$ ) through the physical transfer method to get rid of the Fermi-level pinning effect. In addition, the vertical structure dramatically reduces the channel length to the atomic scale and efficiently collects excited carriers with little recombination loss. Furthermore, the responsivity in those photodiodes is often associated with the light intensity and voltage bias. The thermionic emission theory was employed to explain the impacts of light intensity and voltage bias on the photodiode responsivity. This work can not only improve our fundamental understanding of the photovoltaic and photoconductive effects of 2-D semiconductors but also serve as an important reference for comparing and analyzing photodetectors based on 2-D semiconductors.

Optoelectronic synaptic transistors are advantageous in in-memory light sensing for artificial neural networks. Herein, optoelectronic synaptic junction field-effect transistors (JFETs) based on a Ga2O3/MoS2 heterojunction are fabricated. The devices exhibit robust electrical performances, including a high on/off ratio of 108, a low subthreshold swing of 69 mV dec−1, and a high output current of 3.4 μA μm−1. An inverter and a NAND gate are constructed based on the dual-gated configuration, with the inverter showing a high voltage gain of 28 and the near-ideal noise margin of 90.4%. Additionally, the devices demonstrate outstanding optoelectronic performances benefiting from the strong light–matter interactions of MoS2. Typical synaptic plasticities, including short-term plasticity, long-term plasticity, and spiking-rate-dependent plasticity, are simulated by applying the light pulses. Furthermore, metaplastic excitatory postsynaptic current, metaplastic facilitation of long-term potentiation and transition from potentiation to depression are also readily demonstrated. The artificial neural network, in which neurons are interconnected through our proposed optoelectronic synaptic transistors, achieves a high accuracy of 89.8% in recognizing handwritten digits. This work provides insight into the design of an optoelectronic synapse based on JFETs.

Wide-bandgap (WBG) and ultrawide-bandgap (UWBG) semiconductors are key materials for high-power electronics, radio-frequency electronics, and ultraviolet optoelectronics. However, heterogeneous integration remains challenging because conventional heteroepitaxy is constrained by lattice mismatch and differences in thermal expansion coefficients, while interface states and non-ideal metal–semiconductor contacts can degrade carrier transport and device performance. Two-dimensional (2D) materials offer an important alternative approach to heterogeneous integration. Their dangling-bond-free surfaces and van der Waals interactions relax lattice-matching requirements and facilitate membrane release, while their tunable electronic properties enable control over band alignment and interfacial carrier transport. This review examines the integration of 2D materials with WBG and UWBG semiconductors, focusing on epitaxial growth, interface physics, optoelectronic devices, and scalable integration. Representative 2D material-assisted epitaxial modes include remote, pinhole, and van der Waals epitaxy. Mixed-dimensional heterostructures are discussed in terms of their interfacial electronic properties, contact engineering, passivation strategies, and thermal transport. Photodetection represents an important optoelectronic application of these heterostructures. Taken together, these advances highlight the growing importance of 2D materials in WBG and UWBG integration and point to broader opportunities in future electronics.

The 2-D semiconductors, such as molybdenum disulfide (MoS2), have seen extensive use in the fields of electronics and optoelectronics. However, the lower carrier mobility and weak light absorption ability of the ultrathin layered structure greatly limit commercial applications. In this study, we use a single-step UV-ozone oxidation method to transform flat magnesium (Mg) into a rippled substrate, which effectively enhances the carrier mobility of MoS2 from the range of $19.2\sim 31.2$ to $45.3\sim 78.2$ cm ${}^{{2}} \cdot $ V ${}^{\text {-1}} \cdot $ s ${}^{\text {-1}}$ . Owing to the multiple reflections from peak to peak, the device also demonstrates high photoresponsivity of $1.6\times 10^{{5}}$ A/W. Interestingly, with appropriate gate bias, the device exhibits constant photoresponsivity of ~220 A/W independent of the incident light intensity. This work presents a simple oxidation-induced rippled Mg substrate, which simultaneously addresses low carrier mobility and weak light absorption in 2-D semiconductors, enabling synergistic electrical-optical improvements, paving the way for the design of high-performance optoelectronic devices.