Resonant Tunneling Transistor based on Single PbS Quantum Dot

The growing need for high-performance computing continues to drive circuit and device technologies to improve in terms of speed and power. Device dimension scaling will be the most effective strategy for meeting circuit performance requirements and reducing power consumption. Colloidal semiconductor quantum dots (QDs) are highly suitable to support device miniaturization by solution processability and as platforms for quantum information science¹. The consideration of quantum mechanical effects is crucial in designing nanometer-scale electronic devices (i.e., transistors) that involve single QD. On the other hand, challenges related to the fabrication of such devices require radical solutions. Therefore, developing a bottom-up approach to enable the fabrication of high-quality single QD transistors based on the colloidal process that can easily be contacted electrically is an essential strategy that must be explored.<br/><br/>Here we demonstrate a resonant tunneling transistor (RTT) based on single lead sulfide (PbS) QD as a Coulomb island anchored by ligand molecules that are attached to the Au nanogap electrodes. We are utilizing two different alkane dithiol ligands which have different ligand chain length². We specifically use PbS due to its well-established synthesis process and large electron Bohr radius, thus providing stronger and more stable quantum confinement at the given QD diameters and the well-defined formation of the discrete energy levels³. We develop nanogap electrodes by combining both electron beam lithography and electroless gold plating (ELGP)⁴ to create a robust platform for the single QD device. The robust heterostructure ELGP nanogap electrode provides the capability to apply large voltage bias to the single PbS QD transistor across the two Au electrodes (the source and the drain) without breaking the device, which leads to an excellent yield. It enables us to tune the chemical potential of the PbS QD in and out of resonance with the given band energy. Consequently, we can clearly observe multiple regions of negative differential resistance (NDRs) in the current-voltage (I-V) characteristics of PbS QD devices. In addition, these NDRs can be additionally tuned by the application of a gate electric field. NDR is among the key features that can be used in modern electronic and logic circuits, which are expected to play essential roles in quantum and neuromorphic electronics⁵. This demonstration of single PbS-QD-based RTTs paves the way for the future development of solution-processable quantum electronic devices.<br/><br/>References:<br/>[1] R. D. Septianto, et al., Nature Comm., <b>2023</b>, 14, 2670.<br/>[2] R. D. Septianto, et al., NPG Asia Materials, <b>2020</b>, 12, 33.<br/>[3] L. Liu, et al., Nanoscale, <b>2021</b>, 13, 14001-14007.<br/>[4] V. M. Serdio, et al., Nanoscale,<b> 2012</b>, 4, 7161.<br/>[5] Y. Y. Choi, et al., Appl. Phys. Express, <b>2019</b>, 12, 125007.