CAREER: Realizing ultrahigh mobility semiconductors through light-matter interactions

Non-technical description: The semiconductor technologies that pervade modern society work by transporting energy carriers like electrons and excitons from source to target. Carrier scattering with impurities and vibrations is the primary source of resistance in semiconductors, limiting the speed and efficiency of all electronic devices ranging from photovoltaics to computer chips.

Rising needs for energy efficiency and computing power provide a strong impetus for identifying materials and processes that minimize these scattering losses. This CAREER project leverages novel light-matter interactions to minimize or completely suppress scattering at ambient conditions in two-dimensional semiconductors of high current interest, towards high-speed, nearly resistance-free transport of energy and information.

For the educational component of this project, the research team develops affordable but high-performance optical microscopes capable of detecting single molecules. The microscopes are used in a hands-on microscope building workshop for high school students, and in a new undergraduate laboratory on weighing single molecules with light.

Technical description: When light couples strongly to collective dipole excitations, light and matter excitations are renormalized into part-light part-matter eigenstates known as polaritons. Polaritons inherit the strong nonlinear interactions of matter and the long-range coherence of light. Although seemingly ideal for energy and information transport, polaritons are short-lived and challenging to extract.

This CAREER project focuses on leveraging polaritons to modify the properties of adjacent non-polaritonic charges and excitons, even in the absence of light. This approach circumvents the short lifetimes and poor extraction efficiency of polaritons. The first aim of the project seeks to suppress charge carrier–defect scattering in disordered van der Waals semiconductors through strong coupling between light and electronic excitations.

The second aim harnesses phonon-polaritons in polar dielectrics to accelerate exciton and charge transport in two-dimensional semiconductors across a van der Waals gap. In both cases, the research team uses non-contact ultrafast optical microscopy to directly visualize the motion of charges, excitons and polaritons moving over 10 nanometers–50 microns and 30 femtoseconds–10 microseconds, providing mechanistic insight into polariton-assisted carrier transport.

These measurements are complemented by photocurrent and traditional contact measurements to verify compatibility with standard semiconductor hardware for applications in microelectronics.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.