Dissertation Title: Optoelectronic Devices Based on Two-Dimensional Materials and Their van der Waals Heterojunctions
Date: 2025/05/08 - 2025/05/08
Dissertation Title: Optoelectronic Devices Based on Two-Dimensional Materials and Their van der Waals Heterojunctions
Speaker: Zhentao Lian, Ph.D. candidate at UM-SJTU Joint Institute
Time: 9:00 AM - 10:00 AM, Thursday, May 8, 2025 (Beijing Time)
Location: Room 414B, Longbin Building
Abstract
Two-dimensional (2D) molybdenum disulfide (MoS2) has recently attracted tremendous interest as phototransistors because of their unique optical and electronic characteristics. However, for the phototransistors based on 2D MoS2, the detectable spectral range and the photodetection performance are quite limited. In this dissertation, the author improves the detectable spectral range and the photodetection performance of 2D MoS2 phototransistors through the construction of phototransistors and optoelectronic synapses based on van der Waals heterojunction (vdWH), and photodetectors based on unique structures and mechanisms.
Firstly, the author demonstrates phototransistors based on a vdWH formed by zero-dimensional (0D) silicon quantum dots (SiQDs) and 2D MoS2. Compared to the phototransistor based on monolayer MoS2 alone, the SiQD/monolayer MoS2 vdWH phototransistor exhibits 100 times improvement in detectivity and 89 times improvement in photoresponsivity at UV region (365 nm).
Secondly, to further extend the detectable spectral range of 2D MoS2 phototransistors in the UV, the author reports a high performance deep-ultraviolet (DUV) sensitive phototransistor based on a vdWH formed by the wide bandgap silicon carbide nanoparticles (SiC NPs) and 2D MoS2, which shows ultrahigh photoresponsivity and detectivity, especially in DUV spectral range. Moreover, the biological synaptic behaviors such as short-term plasticity, long-term plasticity, and long-term depression capabilities are successfully emulated by the SiC NPs/few-layer MoS2 vdWH synapse.
Thirdly, the author demonstrates the fast response 2D MoS2 phototransistor based on a doubly-clamped structure. Compared to the basic MoS2 phototransistor, the doubly-clamped 2D MoS2 phototransistors shows a more than 105-fold improvement in response speed. Furthermore, to realize the versatility of the phototransistor, the author demonstrates a dual-mode vdWH photodetector with SiQDs on top of a suspended circular MoS2 membrane. The photoresponsivity and detectivity of hybrid SiQDs/MoS2 device reach 8.1×103 A/W and 4.2×1013 cm×Hz1/2/W under 405 nm illumination, respectively. The hybrid SiQDs/MoS2 device also exhibits a resonance frequency red-shift of 8.7% using optical excitation and 14.3% using electrical excitation, with an enhancement of 378% and 255%, respectively, compared to the pure MoS2 device.
In summary, the high-performance phototransistors based on vdWHs and the photodetectors based on freely suspended membrane structures hold great promises for ultrasensitive photodetection, optical communication, neuromorphic visual sensing and in-sensor computing applications.
Biography
Zhentao Lian received his B.S. degree from China University of Petroleum (UPC) in 2016 and his M.S. degree from East China University of Science and Technology (ECUST) in 2019. He is currently a Ph.D. student at the University of Michigan-Shanghai Jiao Tong University Joint Institute at Shanghai Jiao Tong University. His research focuses on optoelectronic and memory devices based on 2D and 0D materials.