Emerging Two-Dimensional Semiconductors for Electronics and Optoelectronics
Continued miniaturization of electronic circuits and ubiquity for consumer electronics in unconventional format can only be sustained through alternative semiconducting materials to replace crystalline silicon in computer chips and amorphous silicon in large-area displays. Recently, new kinds of two dimensional layered materials have emerged as potential candidates due to their superior electronic, thermal, chemical, and mechanical properties. In particular, sub-nanometer thick films of semiconducting transition metal dichalcogenides show promises for large-area electronic applications such as flexible displays. In this presentation, I will consider the case of single layer molybdenum disulfide (MoS2) for thin-film transistor technologies, photodetectors, and novel electronic device concepts. Single layer MoS2 is a direct band-gap (1.9 eV) semiconductor with high carrier mobility, large switching ratio, and strong photoresponse. In the first half, I will talk about electronic transport mechanisms in single layer MoS2 field-effect transistors probed through an experimental study of electrical conductivity as a function of temperature and electron density. Flicker noise or 1/f noise can also be a limiting factor in nanoscale devices; and thus, I will briefly discuss fundamental origins of 1/f noise in MoS2. To gauge the potential of MoS2 in optoelectronics, the second half of the presentation will show our recent findings on photoresponse in single layer MoS2 transistors and p-n heterojunction diodes. First, scanning photocurrent microscopy will be presented as a powerful tool to distinguish extrinsic and intrinsic effects in photodetection measurements; and then, I will discuss intrinsic photocurrent generation mechanisms in MoS2 transistors. Finally, I will conclude by demonstrating a novel device architecture enabled by two-dimensional semiconductors. In this context, I will show unprecedented device characteristics from a gate-tunable van der Waals heterojunction p-n diode between single layer MoS2 and single walled carbon nanotubes.
Dr. Vinod K. Sangwan is currently a postdoctoral fellow in the groups of Profs. Mark C. Hersam, Lincoln J. Lauhon, and Tobin J. Marks in the Department of Materials Science and Engineering at Northwestern University. He received his B. Tech. in Engineering Physics from Indian Institute of Technology Mumbai in 2002, and Ph.D. in physics from the University of Maryland College Park in 2009. His current research covers electronic and optoelectronic materials and devices. Some key interest areas include growth of unconventional gate-dielectrics for large-area electronics, understanding charge transport and dynamics in low-dimensional semiconductors, and development of novel van der Waals heterojunction devices for electronic and optoelectronic applications.