Semiconductor nanowires conjugate the electronic quality of crystalline materials with the possibility of being dispersed in a solvent. Hence, semiconductor nanowires can be used as building blocks for flexible and integrated electronic devices that can be made at low cost using printing technologies. ZnO nanowires are particularly interesting as they naturally form 1D nanostructures and grow in solution at low temperature while maintaining good electronic properties (mobility ~40 cm2/V.s). Nevertheless, there are still several obstacles to the utilization of nanowires in electronic devices that are due to their nanoscopic nature. Namely, contact doping currently limits the performance of ZnO nanowire field-effect transistors (FETs). Making contact to the outside world by making exclusive use of conventional technologies such as photolithography represents a challenge as well. This collaboration between Stanford University and the Max Planck Institute for Solid-State Physics tackles both these problems by synergistically combining expertises. The Stanford team will grow ZnO nanowires in solution with modulated doping along the nanowire length forming n-i-n structures. As a result, the nanowires will have self-alingned contacts. The length of the intrinsic part of the nanowire, which ultimately determines the switching speed of the nanowire when used in a FET, will be simply controlled by the growth time thus allowing facile synthesis of short-channel FETs with long contacts for easy interfacing to the outside world. The Max Planck Institute team will leverage its expertise in device fabrication, including the development of a unique ultra-thin molecular dielectric suitable for short-channel FET fabrication, in order to test materials and eventually build simple nanowire-based circuits.
Nanowire-based electronics is a very promising technology. This project will help educate students in the science and engineering of an emerging field thus providing immediate societal benefits. The students participating in the project will also benefit from doing research in an international setting. They will be sent to Germany where they will learn the skills of state-of-the-art device fabrication. Conversely, students involved in the research at the Max-Planck Insitute will learn how to use advanced characterization techniques at Stanford. Thus this project will produce extremely well-rounded individuals, with hands-on experience in a broad range of disciplines, from fundamental Materials Science to the physics of electronic devices. Furthermore the project will educate teachers who will visit Stanford during the summer and will be trained on the use of remote electron microscopy capabilities that they will be able to port to their classes by imaging nanowires and nanowire devices with sub-10 nm resolution.
