Source-field-plated Ga_2O_3 MOSFET with a breakdown voltage of 550 V

Ga_2O_3 metal–oxide–semiconductor field-effect transistors(MOSFETs) with high-breakdown characteristics were fabricated on a homoepitaxial n-typed β-Ga_2O_3 film, which was grown by metal organic chemical vapor deposition(MOCVD) on an Fedoped semi-insulating(010) Ga_2O_3 substrate. The structure consisted of a 400 nm unintentionally doped(UID) Ga_2O_3 buffer layer and an 80 nm Si-doped channel layer. A high k HfO_2 gate dielectric film formed by atomic layer deposition was employed to reduce the gate leakage. Moreover, a source-connected field plate was introduced to enhance the breakdown characteristics. The drain saturation current density of the fabricated device reached 101 mA/mm at V_(gs) of 3 V. The off-state current was as low as 7.1 ×10^(-11) A/mm, and the drain current I_(ON)/I_(OFF) ratio reached 10~9. The transistors exhibited three-terminal off-state breakdown voltages of 450 and 550 V, corresponding to gate-to-drain spacing of 4 and 8 μm, respectively.

Ultrafast modulable 2DEG Huygens metasurface

Huygens metasurfaces have demonstrated remarkable potential in perfect transmission and precise wavefront modulation through the synergistic integration of electric resonance and magnetic resonance.However,prevailing active or reconfigurable Huygens metasurfaces,based on all-optical systems,encounter formidable challenges associated with the intricate control of bulk dielectric using laser equipment and the presence of residual thermal effects,leading to limitations in continuous modulation speeds.Here,we present an ultrafast electrically driven terahertz Huygens metasurface that comprises an artificial microstructure layer featuring a two-dimensional electron gas(2DEG)provided by an AlGaN/GaN heterojunction,as well as a passive microstructure layer.Through precise manipulation of the carrier concentration within the 2DEG layer,we effectively govern the current distribution on the metasurfaces,inducing variations in electromagnetic resonance modes to modulate terahertz waves.This modulation mechanism achieves high efficiency and contrast for terahertz wave manipulation.Experimental investigations demonstrate continuous modulation capabilities of up to 6 GHz,a modulation efficiency of 90%,a transmission of 91%,and a remarkable relative operating bandwidth of 55.5%.These significant advancements substantially enhance the performance of terahertz metasurface modulators.Importantly,our work not only enables efficient amplitude modulation but also introduces an approach for the development of high-speed and efficient intelligent transmissive metasurfaces.

Real-time programmable metasurface for terahertz multifunctional wave front engineering

Terahertz(THz)technologies have become a focus of research in recent years due to their prominent role in envisioned future communication and sensing systems.One of the key challenges facing the field is the need for tools to enable agile engineering of THz wave fronts.Here,we describe a reconfigurable metasurface based on GaN technology with an array-of-subarrays architecture.This subwavelength-spaced array,under the control of a 1-bit digital coding sequence,can switch between an enormous range of possible configurations,providing facile access to nearly arbitrary wave front control for signals near 0.34 THz.We demonstrate wide-angle beam scanning with 1°of angular precision over 70 GHz of bandwidth,as well as the generation of multi-beam and diffuse wave fronts,with a switching speed up to 100 MHz.This device,offering the ability to rapidly reconfigure a propagating wave front for beam-forming or diffusively scattered wide-angle coverage of a scene,will open new realms of possibilities in sensing,imaging,and networking.

High-stability _(4)H-SiC avalanche photodiodes for UV detection at high temperatures

In this work,high-stability _[4]H-SiC avalanche photodiodes[APDs]for ultraviolet[UV]detection at high temperatures are fabricated and investigated.With the temperature increasing from room temperature to 150℃,a very small temperature coefficient of 7.4 m V/℃is achieved for the avalanche breakdown voltage of devices.For the first time,the stability of 4H-SiC APDs is verified based on an accelerated aging test with harsh stress conditions.Three different stress conditions are selected with the temperatures and reverse currents of 175℃/100μA,200℃/100μA,and 200℃/500μA,respectively.The results show that our 4H-SiC APD exhibits robust high-temperature performance and can even endure more than120 hours at the harsh aging condition of 200℃/500μA,which indicates that 4H-SiC APDs are very stable and reliable for applications at high temperatures.

High-performance 4H-SiC p-i-n ultraviolet avalanche photodiodes with large active area

Ultraviolet(UV) detectors with large photosensitive areas are more advantageous in low-level UV detection applications. In this Letter, high-performance 4 H-SiC p-i-n avalanche photodiodes(APDs) with large active area(800 μm diameter) are reported. With the optimized epitaxial structure and device fabrication process,a high multiplication gain of 1.4 × 10^6 is obtained for the devices at room temperature, and the dark current is as low as ~10 p A at low reverse voltages. In addition, record external quantum efficiency of 85.5% at 274 nm is achieved, which is the highest value for the reported Si C APDs. Furthermore, the rejection ratio of UV to visible light reaches about 10^4. The excellent performance of our devices indicates a tremendous improvement for largearea SiC APD-based UV detectors. Finally, the UV imaging performance of our fabricated 4 H-SiC p-i-n APDs is also demonstrated for system-level applications.

Dynamic bifunctional THz metasurface via dual-mode decoupling

Metasurfaces have powerful light field manipulation capabilities and have been researched and developed extensively in various fields.With an increasing demand for diverse functionalities,terahertz(THz)metasurfaces are also expanding their domain.In particular,integrating different functionalities into a single device is a compelling domain in metasurfaces.In this work,we demonstrate a functionally decoupled THz metasurface that can incorporate any two functions into one metasurface and switch dynamically through external excitation.This proposed metasurface is formed by the combination of split-ring resonators and phase change material vanadium dioxide(VO_(2)).It operates in the single-ring resonant mode and double-ring resonant mode with varying VO_(2)in insulating and metallic states,respectively.More importantly,the phase modulation is independent in two operating modes,and both cover a 360°cross-polarized phase with efficient polarization conversion.This characteristic makes it obtain arbitrary independent phase information on the metasurface with different modes to switch dual functions dynamically.Here,we experimentally demonstrate the functions of a tunable focal length and large-angle focus deflection of a THz off-axis parabolic mirror to verify the dual-function switching characteristics of the functionally decoupled metasurface.The functionally decoupled metasurface developed in this work broadens the way for the research and application of multifunctional modulation devices in the THz band.

Arbitrary linear THz wave polarization converter with cracked cross meta-surface

This Letter presents a double-layer structure combining a cracked cross meta-surface and grating surface to realize arbitrary incident linear terahertz(THz) wave polarization conversion. The arbitrary incident linear polarization THz wave will be induced with the same resonant modes in the unit cell, which results in polarization conversion insensitive to the linear polarization angle. Moreover, the zigzag-shaped resonant surface current leads to a strong magnetic resonance between the meta-surface and gratings, which enhances the conversion efficiency. The experimental results show that a more than 70% conversion rate can be achieved under arbitrary linear polarization within a wide frequency band. Moreover, around 0.89 THz nearly perfect polarization conversion is realized.