Mingsheng Xu

Neuromorphic computing based on ferroelectric devices has shown great potential in artificial intelligence tasks. However, the challenge of heterogeneous integration between synaptic and neuronal devices has imposed additional limitations on hybrid neural network hardware. In this work, ferroelectric and antiferroelectric devices based on element doping engineering of HfZrOx films are employed to emulate synaptic and neuron functionality for hybrid spiking neural network (SNN) neuromorphic computing. By constructing a functional circuit based on an Hf0.5Zr0.5O2 ferroelectric device, neural characteristics were emulated for SNN computing. Furthermore, the integrate-and-fire dynamics is implemented based on spontaneous depolarization characteristic of a full hafnium-based hybrid ferroelectric neural network, greatly simplifying conventional neuron circuits. The novel neural network architecture achieves a classification accuracy of 92.8% on the Dynamic Vision Sensor dataset, establishing a crucial foundation for the development of high-efficiency neuromorphic computing systems. This work demonstrates considerable promise for realizing hybrid neuromorphic hardware using CMOS-compatible full hafnium-based ferroelectric devices.

Hydrogen-terminated diamond field effect transistors (FETs) are typically depletion-mode devices, which limits their application in low-power-consumption logic circuits. Here, high-performance inverters and ring oscillators have been demonstrated by using normally-off Al/BaF2/H-diamond FETs. The adoption of enhancement-mode transistors enables the realization of low-static-power logic circuits by employing diamond FETs with different channel lengths as load and driver devices. The peak gain of the inverter increases from −100 V/V to −460 V/V as the supply voltage ranges from −1 V to −5 V with a static power consumption low to ~1 pW, marking the highest gain reported for diamond-based inverters. Furthermore, a five-stage ring oscillator operates at 58.8 kHz with a stage delay of 1.7 μs under a supply voltage of −3 V, marking the first successful implementation of a diamond-based ring oscillator. These results highlight the great potential of diamond technology for high-speed power integrated circuit applications.

In this study, we present a high-performance Te/4H-SiC pn heterojunction and its application in self-powered ultraviolet (UV) detector and imaging via a simple thermal evaporation process. The heterojunction demonstrates an ultra-high rectifying ratio of about 10¹³ and a high on-state current density of 393 A/cm². The device also shows excellent UV detection properties with a peak responsivity of 90 mA/W, a detectivity of 6.2×10¹² Jones, and a rapid response time of 90/165 μs at self-powered modes under UV illumination. In addition, the detector exhibits outstanding operational stability. These superior optoelectronic characteristics not only validate its functionality as a UV imaging device but also underscore the strong potential of Te/SiC heterostructures for future cost-effective and energy-effective UV optoelectronic technologies and system integration.

A mixed-dimensional nanobelt/nanosheet heterojunction of CdS/PbI ₂ has been constructed successfully for self-powered flexible and omnidirectional near-ultraviolet photodetection.

In this article, gate bias ( $\textit{V}_{\text{GS},\text{stress}}\text{)}$ effects on the hydrogen (H)-terminated polycrystalline diamond field effect transistors (FETs) are investigated. A 7-to 8-nm AlO $_{\text{x}}$ interface layer is found between the Al metal and polycrystalline diamond by electrical and microstructure characterization. The threshold voltage ( $\textit{V}_{\text{TH}}\text{)}$ and ON-resistance ( $\textit{R}_{\text{on}}\text{)}$ exhibit different changing trends under varying $\textit{V}_{\text{GS},\text{stress}}$ . Specifically, a bidirectional shift of $\textit{V}_{\text{TH}}$ is observed during gate bias stress. To explain the distinct behavior of $\textit{V}_{\text{TH}}$ shift and $\textit{R}_{\text{ON}}$ change occurring under gate bias, holes trapping by defects, H-motion, and surface leakage electron trapping models are proposed. Under negative gate bias, holes in 2-D hole gas channel are captured by the interface states and/or defects in the AlO $_{\text{x}}$ layer, resulting in a negative shift of V $_{\text{TH}}$ . Simultaneously, H-motion in the AlOx layer under gate bias leads to the generation of negative charges. Additionally, electrons in the surface leakage path are trapped by defects on the diamond surface in the access region, leading to decreased access region resistance. For a harsh gate bias, a high density of new defects is generated, and a defect density changes from 4.9 $\times$ 10 $^{\text{21}}$ ev $^{-\text{1}}$ cm $^{-\text{3}}$ for the fresh device to 5.1 $\times$ 10 $^{\text{23}}$ ev $^{-\text{1}}$ cm $^{-\text{3}}$ for the device after gate bias ( $\textit{V}_{\text{GS},\text{stress}}$ $=$ $-$ 4 V) which is characterized by using the low-frequency noise measurements. These findings highlight the importance of surface passivation and high-quality gate dielectric in suppressing charging effects and new defect generation in H-terminated polycrystalline diamond FETs, ultimately contributing to device stability.

In the field of diamond MESFETs, this work is what we believe to be the first to investigate the optoelectronic properties of hydrogen-terminated polycrystalline diamond MESFETs under visible and near-UV light irradiation. It is shown that the diamond MESFETs are well suited for weak light detection in the near-ultraviolet region around the wavelength of 368 nm, with a responsivity of 6.14 x 10(6) A/W and an external quantum efficiency of 2.1 x 10(7) when the incident light power at 368.7 nm is only 0.75 mu W/cm(2). For incident light at 275.1 nm, the device's sensitivity and EQE increase as the incident light power increases; at an incident light power of 175.32 mu W/cm(2) and a VGS of -1V, the device's sensitivity is 2.9 x 10(5) A/W and the EQE is 1.3 x 10(6). For incident light in the wavelength range of 660 nm to 404 nm with an optical power of 70 mu W/cm(2), the device achieves an average responsivity of 1.21 x 10(5) A/W. This indicates that hydrogen-terminated polycrystalline diamond MESFETs are suitable for visible and near-UV light detection, especially for weak near-UV light detection. However, the transient response test of the device shows a long relaxation time of about 0.2 s, so it is not yet suitable for high-speed UV communication or detection. (c) 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

In recent years, because of stringent needs in the fabrication of silicon carbide (SiC) power devices, laser annealing has been introduced to achieve local ohmic contact. In this paper, the laser annealing research for the ohmic contact process of SiC power devices is reviewed, which is mainly divided into four aspects: laser process mechanism, ohmic contact electrode materials, and substrate materials. The effect of laser parameters on ohmic contact and the annealing process on SiC diode devices is also reviewed. Progress of other substrate materials, namely 6H-SiC and semi-insulating 4H-SiC-based devices with laser annealed ohmic contacts, is also briefly discussed, in which formation of semi-insulating SiC ohmic contacts is derived from laser irradiation at the interface to produce 3C-SiC. Some experiment results have been shown in the passage, such as XRD, SEM, TEM, etc. In the review, it points out that the direction of application and development of the laser annealing process for improving the ohmic contact of SiC power devices is highly encouraging.

With the increased power density of gallium nitride (GaN) high electron mobility transistors (HEMTs), effective cooling is required to eliminate the self-heating effect. Incorporating diamond into GaN HEMT is an alternative way to dissipate the heat generated from the active region. In this review, the four main approaches for the integration of diamond and GaN are briefly reviewed, including bonding the GaN wafer and diamond wafer together, depositing diamond as a heat-dissipation layer on the GaN epitaxial layer or HEMTs, and the epitaxial growth of GaN on the diamond substrate. Due to the large lattice mismatch and thermal mismatch, as well as the crystal structure differences between diamond and GaN, all above works face some problems and challenges. Moreover, the review is focused on the state-of-art of polycrystalline or nanocrystalline diamond (NCD) passivation layers on the topside of GaN HEMTs, including the nucleation and growth of the diamond on GaN HEMTs, structure and interface analysis, and thermal characterization, as well as electrical performance of GaN HEMTs after diamond film growth. Upon comparing three different nucleation methods of diamond on GaN, electrostatic seeding is the most commonly used pretreatment method to enhance the nucleation density. NCDs are usually grown at lower temperatures (600–800 °C) on GaN HEMTs, and the methods of “gate after growth” and selective area growth are emphasized. The influence of interface quality on the heat dissipation of capped diamond on GaN is analyzed. We consider that effectively reducing the thermal boundary resistance, improving the regional quality at the interface, and optimizing the stress–strain state are needed to improve the heat-spreading performance and stability of GaN HEMTs. NCD-capped GaN HEMTs exhibit more than a 20% lower operating temperature, and the current density is also improved, which shows good application potential. Furthermore, the existing problems and challenges have also been discussed. The nucleation and growth characteristics of diamond itself and the integration of diamond and GaN HEMT are discussed together, which can more completely explain the thermal diffusion effect of diamond for GaN HEMT and the corresponding technical problems.