Recently, a joint team led by Professor Liu Zewen of the Institute of Microelectronics at Tsinghua University and Associate Professor Deng Tao of the School of Electronic and Information Engineering at Beijing Jiaotong University published a research paper entitled "Three-Dimensional Graphene Field-Effect Transistors as High Performance Photodetectors" in the internationally renowned academic journal *Nano Letters*. This paper describes the fabrication of a microtubular three-dimensional graphene field-effect transistor (3D GFET) using a self-rolling method. This transistor can be used as a photodetector, achieving ultra-high sensitivity and ultra-fast detection of ultraviolet, visible, mid-infrared, and terahertz waves.
Schematic diagram of a high-performance photoelectric sensor based on a three-dimensional graphene field-effect transistor.
Optoelectronic sensors are core components in many fields such as optical communication, imaging, and sensing. Graphene, with its unique zero-bandgap structure and ultrafast carrier mobility, is an ideal material for manufacturing high-performance optoelectronic sensors. Traditional graphene optoelectronic sensors mostly employ planar two-dimensional (2D) GFET structures, which possess ultrawide bandwidth and ultrafast response speed. However, due to the light absorption rate of a single layer of graphene being only 2.3%, the responsivity of 2D GFET optoelectronic sensors is very low (~6.3 mA/W). Although combining graphene with photosensitive materials can significantly improve the responsivity of optoelectronic sensors, the bandwidth and response speed are severely compromised.
This research proposes a method for driving 2D GFETs to self-roll into microtubular 3D GFET structures using silicon nitride stress layers, achieving for the first time the fabrication of 3D GFET device arrays with precisely controllable roll-up layer numbers (1-5) and radii (30 μm-65 μm). This 3D GFET can be used as a photoelectric sensor, operating in a wavelength range extending from the ultraviolet (325 nm) region to the terahertz (119 μm) region, representing the highest bandwidth reported for graphene-based photoelectric sensors. Simultaneously, this 3D GFET exhibits both ultra-high responsivity and ultra-fast response speed, achieving a responsivity exceeding 1 A/W in the ultraviolet-visible region and a responsivity as high as 0.23 A/W in the terahertz region, with a response time as fast as 265 ns (nanoseconds). The fabrication method proposed in this study not only paves the way for the realization of 3D graphene optoelectronic devices and systems but can also be extended to other graphene-like 2D crystalline materials such as molybdenum disulfide and black phosphorus. The reviewers highly praised the research findings, believing that the research is of great significance to the entire field of two-dimensional materials research.
The first author of this paper is Associate Professor Tao Deng, a 2015 graduate of the Department of Microelectronics at Tsinghua University and currently the School of Electronic and Information Engineering at Beijing Jiaotong University. Professor Zewen Liu of the Institute of Microelectronics at Tsinghua University and Associate Professor Tao Deng of the School of Electronic and Information Engineering at Beijing Jiaotong University are the corresponding authors. This research was supported by the National Natural Science Foundation of China, the Beijing Natural Science Foundation, and the Fundamental Research Funds for the Central Universities.
