(Invited) Optoelectronic Application of Colloidal Quatum Dots in Infrared Beyond Si

Abstract

Among electromagnetic wave spectrum, infrared region has many attractive applications such as a LiDAR, optical communication, telecommunications, thermography, bioimaging, photovoltaics, and night visions. However, the expensive cost of epitaxial III-V semiconductors and the fabrication process hinders the widespread of the infrared technology beyond the silicon absorption range. Colloidal quantum dots have a great potential as an alternative materials for infrared detection. Lead chalcogenide QDs not only have tunable bandgap in infrared region but also have process compatibility with conventional Si ROIC in the device fabrication process, which remarkably reduces fabrication costs. The performance of photodetectors incorporating the lead chalcogenide QDs, however, is suboptimal and needs further improvement. One of the main factors limiting the performance of QD-based photodetectors is a high density of surface defects. QDs inherently have large surface-to-volume ratios and dangling bonds on the surface acted as trap sites. Various methods to reduce surface defects, such as thermal and ligand treatment, have been introduced; however, even after these treatments, QD-based photodetectors still show the relatively low detectivity (D*). In this work, we demonstrate the various approaches to improve the performance of infrared photodetectors and their results. We focused on the reducing the trap density by the surface treatment of QDs using thermal annealing and chemical treatment in order to improve the device performance. We developed the chemical treatment method for reducing trap states with maintaining the existing ligands. Thermal annealing also can reduce the trap density; however, it sintered QDs by atomic diffusion. We found optimal condition for reducing the surface traps with suppressing sintering. The effects of these treatments were evaluated by the device performance and trap characterization. These approaches improve the bandwidth and the responsivity compared to reference devices. Moreover, we treated the surface of QD layers to show the interfacial effect on the QD devices.