Kai Hu

Nanostructured Photodetectors: From Ultraviolet to Terahertz

Inspired by nanoscience and nanoengineering, numerous nanostructured materials developed by multidisciplinary approaches exhibit excellent photoelectronic properties ranging from ultraviolet to terahertz frequencies. As a new class of building block, nanoscale elements in terms of quantum dots, nanowires, and nanolayers can be used for fabricating photodetectors with high performance. Moreover, in conjunction with traditional photodetectors, they exhibit appealing performance for practical applications including high density of integration, high sensitivity, fast response, and multifunction. Therefore, with the perspective of photodetectors constructed by diverse low-dimensional nanostructured materials, recent advances in nanoscale photodetectors are discussed here; meanwhile, challenges and promising future directions in this research field are proposed.

A surface oxide thin layer of copper nanowires enhanced the UV selective response of a ZnO film photodetector

Copper nanowires (Cu NWs) with good crystallinity and high aspect ratio were prepared by a facile hydrothermal method at low temperature, and they were dispersed on a smooth and thin layer of ZnO film to construct a photodetector (PD). This Cu NW/ZnO PD exhibits a remarkably higher UV-visible rejection ratio (∼160), which is almost 13 times that of a bare ZnO PD (12.5) and more than twice that of a Cu film/ZnO PD (67.7). The high UV light selective response of the Cu NW/ZnO PD is caused by the dramatic decrease of the photoresponsivity in the visible light region and the high photocurrent in the UV region due to the presence of a potential barrier between ZnO and Cu NWs. Interestingly, the commonly observed thin layer of CuO (2 nm) on the surface of Cu NWs plays a significant role in the enhanced UV light selective response performance. The results demonstrate that the height of the Schottky barrier and the thickness of the depletion layer are both reduced owing to the oxidized copper layer, which leads to the excellent UV selective response. Our results indicate that Cu NWs, as a multifunctional material, could have diverse applications in the field of optoelectronics. And this detector obtained by a simple preparation method shows great potential in the actual applications in the future.

Ultrasensitive Self‐Powered Solar‐Blind Deep‐Ultraviolet Photodetector Based on All‐Solid‐State Polyaniline/MgZnO Bilayer

A high sensitivity self-powered solar-blind photodetector is successfully constructed based on the polyaniline/MgZnO bilayer. The maximum responsivity of the photodetector is 160 μA W-1 at 250 nm under 0 V bias. The device also exhibits a high on/off ratio of ≈104 under 250 nm illumination at a relatively weak light intensity of 130 μW cm-2 without any power.

Novel UV–Visible Photodetector in Photovoltaic Mode with Fast Response and Ultrahigh Photosensitivity Employing Se/TiO2 Nanotubes Heterojunction

A feasible strategy for hybrid photodetector by integrating an array of self-ordered TiO2 nanotubes (NTs) and selenium is demonstrated to break the compromise between the responsivity and response speed. Novel heterojunction between the TiO2 NTs and Se in combination with the surface trap states at TiO2 help regulate the electron transport and facilitate the separation of photogenerated electron-hole pairs under photovoltaic mode (at zero bias), leading to a high responsivity of ≈100 mA W-1 at 620 nm light illumination and the ultrashort rise/decay time (1.4/7.8 ms). The implanting of intrinsic p-type Se into TiO2 NTs broadens the detection range to UV-visible (280-700 nm) with a large detectivity of over 1012 Jones and a high linear dynamic range of over 80 dB. In addition, a maximum photocurrent of ≈107 A is achieved at 450 nm light illumination and an ultrahigh photosensitivity (on/off ratio up to 104 ) under zero bias upon UV and visible light illumination is readily achieved. The concept of employing novel heterojunction geometry holds great potential to pave a new way to realize high performance and energy-efficient optoelectronic devices for practical applications.

Photoelectric Detectors Based on Inorganic p‐Type Semiconductor Materials

Photoelectric detectors are the central part of modern photodetection systems with numerous commercial and scientific applications. p-Type semiconductor materials play important roles in optoelectronic devices. Photodetectors based on p-type semiconductor materials have attracted a great deal of attention in recent years because of their unique properties. Here, a comprehensive summary of the recent progress mainly on photodetectors based on inorganic p-type semiconductor materials is presented. Various structures, including photoconductors, phototransistors, homojunctions, heterojunctions, p-i-n junctions, and metal-semiconductor junctions of photodetectors based on inorganic p-type semiconductor materials, are discussed and summarized. Perspectives and an outlook, highlighting the promising future directions of this research field, are also given.

Size-Controlled Graphene Nanodot Arrays/ZnO Hybrids for High-Performance UV Photodetectors

Abstract Graphene nanodots (GNDs) are one of the most attractive graphene nanostructures due to their tunable optoelectronic properties. Fabricated by polystyrene‐nanosphere lithography, uniformly sized graphene nanodots array (GNDA) is constructed as an ultraviolet photodetector (PD) with ZnO nanofilm spin coated on it. The size of GNDA can be well controlled from 45 to 20 nm varying the etching time. It is revealed in the study that the photoelectric properties of ZnO/GNDA PD are highly GNDA size‐dependent. The highest responsivity (R) and external quantum efficiency of ZnO/GNDA (20 nm) PD are 22.55 mA W−1 and 9.32%, almost twofold of that of ZnO PD. Both ZnO/GNDA (20 nm) PD and ZnO/GNDA (30 nm) PD exhibit much faster response speed under on/off switching light and have shorter rise/decay time compared with ZnO PD. However, as the size of GNDA increase to 45 nm, the PD appears poor performance. The size‐dependent phenomenon can be explained by the energy band alignments in ZnO/GNDA hybrids. These efforts reveal the enhancement of GNDs on traditional photodetectors with tunable optoelectronic properties and hold great potential to pave a new way to explore the various remarkable photodetection performances by controlling the size of the nanostructures.