image: Schematic illustration of the nanowire structures, operation of nanowire-based photoelectrochemical photodetectors under different light illumination and the corresponding chemical reaction process at nanowire surface: Top: p-AlGaN/n-GaN nanowire; Bottom: a-MoSx decorated p-AlGaN/n-GaN nanowire. During operation, the photoresponse signal of the photoelectrochemical device is determined by the number of photo-generated carriers which effectively participate in the redox reactions, and the photocurrent polarity (either positive or negative) is determined by the type of predominate redox reaction triggered at solid/liquid interface. In other words, depending on the wavelength of the incident light, either hydrogen evolution reaction (HER) or oxygen evolution reaction (OER) will dominate in the photoelectrochemical photodetector, leading to the switch of photoconductivity. view more
Credit: by Danhao Wang, Wentiao Wu, Shi Fang, Yang Kang, Xiaoning Wang, Wei Hu, Huabin Yu, Haochen Zhang, Xin Liu, Yuanmin Luo, Jr-Hau He, Lan Fu, Shibing Long, Sheng Liu and Haiding Sun
III-V semiconductor nanowires possess fascinating material properties, which pave the way towards the fabrication of next-generation nanoscale electronic and optoelectronic devices. In particular, owing to their distinctive nanostructure nature, III-V nanowires exhibit unique properties that do not exist in their bulk form. Such remarkable one-dimensional geometry provides us great opportunities to leverage their surface characteristics (for example, through surface decoration or modification by a functional layer) to spark new phenomenon which is barely attainable in conventional nanowires, paving the way for developing next-generation nanoscale electronic and optoelectronic devices.
In a new paper published in Light Science & Application, a team of scientists, led by Professor Haiding Sun, School of Microelectronics at University of Science and Technology of China and co-workers have combined earth-abundant molybdenum sulfides with the popular group III-nitride semiconductor nanowires to form III-nitride/a-MoSx core-shell nanostructures which demonstrate negative photoresponsivity under 254 nm illumination and positive photoresponsivity under 365 nm illumination, which is rarely seen in traditional III-nitride nanowires.
“Photodetectors measure photon flux or optical power by converting the absorbed photon energy into electrical current, so-called photocurrent. In the operation of a photodetector, it is highly desirable that we can use the generated photocurrent, not only its magnitude but also its directionality to measure and diagnose the incident light signals. Consequently, once the photodetector demonstrates a dual-polarity photocurrent behavior upon different wavelength light illumination, we are able to distinguish different spectra bands.” Herein, Prof. Sun collaborated with other scientists and they propose to form III-nitride/MoSx core-shell nanowires for constructing spectrally sensitive photoelectrochemical photodetectors. Essentially, such a monolithically integrated core-shell nano-device architecture not only address issues of the nanowire surface states, but also expand the device functionalities by unleashing the full potential of both types of low-dimensional materials. As a result, the new a-MoSx/GaN core-shell nano-architecture propels superior device performance, exhibiting a benchmarking negative photoresponsivity of -100.42 mA·W−1 under 254 nm, and a positive photoresponsivity of 29.5 mA·W−1 under 365 nm illumination, which represents one of the best devices among the reported spectrally distinctive photosensors.”
“This vertical nanowire p-n heterojunction configuration based photoelectrochemical device presents a new universal photodetector architecture with ultrabroad wavelength coverage and selectivity that can span ultraviolet, visible, and/or infrared spectral range by constructing nanowire p-n heterojunctions composed of any binary or ternary III-V semiconductors (III- nitrides, arsenides, and phosphides etc.). This is ascribed to the unique one-dimensional structure of nanowires, which allows sufficient strain relaxation for epitaxial growth of a broad range of lattice-mismatched materials.” they added.
“The presented technique can be used in multiple-band and spectrally distinctive photodetection in building modern light-induced sensing systems, including colorful and filter-less imaging, portable spectrometer, artificial vision, bio-sensors and optically-controlled logic circuits. Particularly, for those emerging photoelectrochemical-type (PEC-type) photodetectors, they can be directly implemented in aqueous condition, such as in bio blood environment, seawater or underwater environment for light communication, photo-sensing and bio-detection, as compared with those conventional solid-state photodetectors that requires sophisticated packaging for aqueous application.” the scientists explain.
Journal
Light Science & Applications