Infrared photodetectors based on graphene and other two-dimensional materials

• Main Author: Yu, Xuechao
• Other Authors: School of Electrical and Electronic Engineering
• Format: Theses and Dissertations
• Language: English
• Published: 2016
• Subjects: DRNTU::Engineering::Electrical and electronic engineering::Optics, optoelectronics, photonics
• Online Access: http://hdl.handle.net/10356/68895
• Institution: Nanyang Technological University

Infrared photodetector is a key component in the development of modern infrared technologies, ranging from imaging, sensing and optical communication and so on. However, they are limited by the limited materials available and their scaling, integrability and cost. Graphene and other two-dimensional materials that are recently discovered and demonstrated to possess unique physical properties are promising candidates for various types of photodetectors ranging from UV, infrared and up to terahertz wavelengths. In this thesis, we will focus on developing infrared photodetectors based on graphene and other two-dimensional materials. First, a novel strategy to improve the performance of graphene photodetectors is enhancing the absorption by opening a bandgap of ~ 100 meV in graphene which is suitable for mid-infrared photodetections. Although patterning graphene into nanostructures with quantum confinement effect is able to open a bandgap, devices based on these graphene nanostructures generally suffer from low carrier mobility and high scattering loss. Here we demonstrate that encapsulation of atomic layer deposited high-quality HfO2 film will greatly enhance the carrier mobility and decrease the scattering loss of graphene nanoribbon, because this high-k dielectric layer weakens carrier Coulombic interactions. In addition, photodetector based on HfO2 layer capped graphene nanoribbons can cover a broadband wavelength from visible to mid-infrared at room temperature. On the other hand, the scattering loss can be also modified by decorating electron trapping layers, such as the well-known electron trapper C60 demonstrated in our work. We fabricate graphene nanoribbon-C60 hybrid based mid-infrared photodetector, which was able to achieve high photoresponsivity of 0.4 A/W in the mid-infrared, due to the high electron trapping efficiency of C60 on sub-10 nm graphene nanoribbon while photogenerated holes circulating in the channel. Even though graphene-based photodetectors show the broadband operation property for visible to the mid-infrared, the response time and detectivity are relatively low. To address these issues, we propose and develop several novel infrared photodetectors with other alternative two-dimensional semiconducting materials. An ambient stable, in-plane black phosphorene P-N junction is fabricated by partially chemical doped with benzyl viologen and is demonstrated as an efficient near-infrared photodetector as the photogenerated electron-hole pairs can be separated by the built-in electric field. The photocurrent and the detectivity of black phosphorene based photodetectors show remarkable improvement compared to pure graphene photodetectors, but they lack in broadband operation which is limited by their intrinsic bandgap. Inspired by this we synthesize large crystal PtSe2 and fabricated atomic layered PtSe2, a narrow bandgap 2D semiconductor with remarkable carrier mobility, and obtain that the PtSe2 photodetectors with high photoresponsivity under mid-infrared laser illuminations. Based on the above results in mid-infrared photodetectors, we also extend our strategies to develop materials for visible photodetectors. We synthesize large crystal SnSe2 by the chemical vapor deposition method and achieved a high-performance visible photodetector with atomic layered SnSe2 displaying a good responsivity of 0.5 AW-1 and a fast photoresponse down to ~2 ms at room temperature. It is expected that high performance and broadband photodetectors based on graphene and other semiconducting two-dimensional materials will find significant applications in various emerging areas of infrared optoelectronic and photonic fields.