High-performance metal-semiconductor-metal deep-ultraviolet photodetectors based on homoepitaxial diamond thin film

We report high performance visible-blind GaN-based p-i-n photodetectors grown by metal-organic chemical vapor deposition on c -plane sapphire substrates. The dark current of the 200 μm diameter devices was measured to be lower than 20 pA for bias voltages up to 5 V. The breakdown voltages were higher than 120 V. The responsivity of the photodetectors was ∼0.23 AW at 356 nm under 5 V bias. The ultraviolet-visible rejection ratio was 6.7× 103 for wavelengths longer than 400 nm. © 2008 American Institute of Physics

Methods for designing frequency selective surface for optical windows are analyzed and experimentally verified. Four methods; ITO coatings, graphene, metallic nano-coatings and metallic meshes; are compared in terms of optical transmission and shielding effectiveness (SE) characteristics. ITO is the most common method for increasing SE performance in the visible band. However, in the infrared band, transmission of ITO is limited. Metallic nano-coating is an alternative for ITO with underperformance from the SE and optical transmission viewpoint. Graphene is an emerging method and needs further development. SE performance of the graphene prevents from being a single material for shielding applications. On the other hand, it might be involved in applications where back reflection is critical because of the electromagnetic absorption characteristic. Metallic mesh is a successful candidate for applications require high level SE and optical transmission. However, dielectric properties of substrate the mesh applied, and diffraction effects should be carefully investigated.

Thermal imaging at the infrared wavelength regime has long been applied to different areas such as agriculture and defense industries. Metasurfaces, 2D engineered ultra-thin structures, have attracted much attention due to their compact size, superior performance, and different functionalities at optical frequencies. This work details the design and fabrication of high transmission metalenses operating at the long-wave infrared (LWIR) spectrum. We minimize the reflection losses through anti-reflection coating (ARC) while maintaining the full wavefront control at the central wavelength 9.07 µm. Our unit cell structure provides an average transmission of 97.5%. We experimentally verify our results and show that the fabricated metalenses perform diffraction-limited imaging at the design wavelength.

Thermal imaging, particularly LWIR imaging, has several applications in commercial and security systems. The fundamental problem with the development of metalens is the lack of appropriate materials for LWIR applications. The development of silicon metalens is hampered by the material's own LWIR spectral band absorption, although silicon is the ideal material for lithography due to its widespread use in CMOS applications. In this study, metalens working on LWIR spectral band has been designed and fabricated using the highly suitable material germanium and low-cost silicon. The focusing and imaging capacity of two types of metasurfaces has been investigated, and a comparison of the results has been presented in the paper.