Gong Wei, Wang Peng, Deng Wenjie, Zhang Xiaobo, An Boxing, Li Jingjie, Sun Zhaoqing, Dai Dichao, Liu Zekang, Li Jingzhen, Zhang Yongzhe
Faculty of Materials and Manufacturing, Key Laboratory of Advanced Functional Materials, Ministry of Education, Beijing University of Technology, Beijing 100124, China.
Faculty of Information Technology, Key Laboratory of Opto-Electronics Technology, Ministry of Education, Beijing University of Technology, Beijing 100124, China.
ACS Appl Mater Interfaces. 2022 Jun 8;14(22):25812-25823. doi: 10.1021/acsami.2c06620. Epub 2022 May 26.
Lead sulfide colloidal quantum dots (PbS CQDs) have shown great potential in photodetectors owing to their promising optical properties, especially their strong and tunable absorption. However, the limitation of the specific detectivity (*) in CQD near-infrared (NIR) photodetectors remains unknown due to the ambiguous noise analysis. Therefore, a clear understanding of the noise current is critically demanded. Here, we elucidate that the noise current is the predominant factor limiting *, and the noise is highly dependent on the trap densities in halide-passivated PbS films and the carriers injected from the Schottky contact (EDT-passivated PbS films/metal). It is found that the thickness of CQDs is proportional to their interface trap density, while it is inversely proportional to their minimal bulk trap density. A balance point can be reached at a certain thickness (136 nm) to minimize the trap density, giving rise to the improvement of *. Utilizing thicker PbS-EDT films broadens the width of the tunneling barrier and thereby reduces the carrier injection, contributing to a further enhancement of *. The limiting factors of * determined in this work not only explain the physical mechanism of the influence on detection sensitivity but also give guidance to the design of high-performance CQD photodetectors.
硫化铅胶体量子点（PbS CQDs）因其具有良好的光学性能，特别是其强吸收和可调节吸收特性，在光电探测器中显示出巨大潜力。然而，由于噪声分析不明确，CQD近红外（NIR）光电探测器中比探测率（）的限制仍然未知。因此，迫切需要清楚地了解噪声电流。在此，我们阐明噪声电流是限制的主要因素，并且噪声高度依赖于卤化物钝化的PbS薄膜中的陷阱密度以及从肖特基接触（EDT钝化的PbS薄膜/金属）注入的载流子。研究发现，CQDs的厚度与其界面陷阱密度成正比，而与其最小体陷阱密度成反比。在一定厚度（136 nm）时可以达到一个平衡点，以最小化陷阱密度，从而提高*。使用更厚的PbS-EDT薄膜拓宽了隧穿势垒的宽度，从而减少了载流子注入，有助于进一步提高*。这项工作中确定的*的限制因素不仅解释了对检测灵敏度影响的物理机制，还为高性能CQD光电探测器的设计提供了指导。
