Joint International Research Laboratory of Information Display and Visualization, School of Electronic Science and Engineering, Southeast University, Nanjing, 210096, P. R. China.
Electrical Engineering Division, Department of Engineering, University of Cambridge, Cambridge, CB3 0FA, UK.
Adv Mater. 2018 Feb;30(7). doi: 10.1002/adma.201705880. Epub 2018 Jan 8.
Inverse photoresponse is discovered from phototransistors based on molybdenum disulfide (MoS ). The devices are capable of detecting photons with energy below the bandgap of MoS . Under the illumination of near-infrared (NIR) light at 980 and 1550 nm, negative photoresponses with short response time (50 ms) are observed for the first time. Upon visible-light illumination, the phototransistors exhibit positive photoresponse with ultrahigh responsivity on the order of 10 -10 A W owing to the photogating effect and charge trapping mechanism. Besides, the phototransistors can detect a weak visible-light signal with effective optical power as low as 17 picowatts (pW). A thermally induced photoresponse mechanism, the bolometric effect, is proposed as the cause of the negative photocurrent in the NIR regime. The thermal energy of the NIR radiation is transferred to the MoS crystal lattice, inducing lattice heating and resistance increase. This model is experimentally confirmed by low-temperature electrical measurements. The bolometric coefficient calculated from the measured transport current change with temperature is -33 nA K . These findings offer a new approach to develop sub-bandgap photodetectors and other novel optoelectronic devices based on 2D layered materials.
反向光响应是从基于二硫化钼 (MoS ) 的光电晶体管中发现的。这些器件能够检测能量低于 MoS 带隙的光子。在近红外 (NIR) 光 980nm 和 1550nm 的照射下，首次观察到具有短响应时间 (50ms) 的负光响应。在可见光照射下，由于光栅效应和电荷俘获机制，光电晶体管表现出超高响应度的正光响应，响应度高达 10 -10 A W。此外，光电晶体管可以检测到有效光功率低至 17 皮瓦 (pW) 的弱可见光信号。提出了一种热诱导光响应机制，即测辐射热计效应，作为 NIR 区域负光电流的原因。NIR 辐射的热能被转移到 MoS 晶格，引起晶格加热和电阻增加。通过低温电测量实验证实了该模型。从测量的传输电流随温度的变化计算出的测辐射热计系数为 -33nA K。这些发现为开发基于二维层状材料的亚带隙光电探测器和其他新型光电设备提供了一种新方法。
