博士论文答辩：基于二维半导体的光电子器件的机理和特性研究
日期：2025/05/08 - 2025/05/08
博士论文答辩：基于二维半导体的光电子器件的机理和特性研究
主讲人：Jianyong Wei, Ph.D. candidate at UM-SJTU Joint Institute
时间：2025年5月8日（周四）上午10:00-11:00
地点：龙宾楼414B会议室
讲座摘要
In the past decade, photodetectors, especially phototransistors, based on two-dimensional (2D) semiconducting transition metal dichalcogenides (TMDCs) have achieved high photoresponsivity and detectivity for excellent optical and electrical properties, including atomic-scale thickness, tunable bandgap and high carrier mobility. However, there is still a lack of analytical photoresponse model of phototransistors based on 2D semiconductors and the 2D phototransistors are still suffering from low response speed and high noise level. Therefore, this dissertation conducts a systematic investigation of photoresponse mechanisms of 2D phototransistors and aims to improve photoresponse characteristics by leveraging the mechanisms.
Firstly, the additional photogating effect induced by back silicon gate has been demonstrated in 2D phototransistors and a silicon PN junction is further employed instead of the highly doped silicon, resulting in a highly enhanced photoresponse and a widened photodetection range extended to the near-infrared region. Apart from photogating effect in the channel, the significant impact of contact parts on device performance has been studied in Schottky-junction-based 2D phototransistors. Then an analytical photoresponse equation for the MoS2 phototransistors is further established based on the photo-induced Schottky barrier reduction, which is widely applicable to phototransistors dominated by Schottky junctions. Furthermore, multiple types of photoresponse are comprehensively analyzed by designing devices with different channel structures and contact types, and con-ducting four-probe measurement under illumination. Additionally, to enhance the photoresponse speed, the author designs and implements a 2D phototransistor with a fully suspended channel, to avoid the photogating effect in the channel while harnessing the photo-induced Schottky barrier re-duction at the contact. This suspended device shows ultra-low noise level and ultra-fast photoresponse speed with rise time and fall time of 68.6 and 100.0 microseconds, respectively, which are about 105 times faster than the non-suspended devices. Furthermore, based on Ohmic-contact phototransistors, a unique light-intensity-dependent ambipolar photoresponse has been observed. The response type can be transformed between positive and negative by controlling the light intensity. The phototransistor exhibits extremely strong detection capability for weak light with an ultra-high photoresponsivity of 6×104 A/W. The unique ambipolar photoresponse and ultra-high responsivity make the phototransistor promising for practical applications in photodetection.
In conclusion, this dissertation provides fundamental understanding of the photoresponse mechanisms of phototransistors based on 2D semiconductors, and paves the way for further advancements in the exploration of high-performance 2D photodetectors.
主讲人介绍
Jianyong Wei received his BS degree from Beijing University of Posts and Telecommunications in 2015 and MS degree from Zhengzhou University in 2020. He is currently a Ph.D. student in the University of Michigan-Shanghai Jiao Tong University Joint Institute at Shanghai Jiao Tong University. His research focuses on optoelectronic devices and nano-electromechanical system.