Imaging Non-Equilibrium Hot Carrier Dynamics in 2D Materials and Their Heterostructures with Scanning Ultrafast Electron Microscopy-Novel Functional Materials
Abstract
Major Goals: Background: Photocarrier dynamics in emerging low-dimensional and quantum materials are not only crucial for the development of next-generation photovoltaic cells, photo-sensors and other optoelectronics devices, but also of fundamental interest for understanding the non-equilibrium coupling of unusual electron and phonon states. Immediately after electron-hole pairs are photo-excited in semiconductors, they are transiently in a highly non-equilibrium state and possess excessive kinetic energy (effectively described by a high electronic temperature of thousands of degrees). In this short-lived state (femtosecond to picosecond level), the hot photocarriers can exhibit unusual properties, including superdiffusion with a diffusivity several orders of magnitude higher than the equilibrium value. This hot carrier transport effect is further amplified in two-dimensional materials due to the limited phase space for electron-phonon interaction that cools down the hot photocarriers. If this hot carrier transport regime can be effectively probed, modeled, and harnessed, devices with significantly enhanced efficiency and performance can be designed. For example, it has been proposed that if the initial kinetic energy of the hot photocarriers can be collected by a photovoltaic cell, a much higher power conversion efficiency can be achieved than the standard Shockley-Queisser limit. Effective capture of the hot photocarrier's excessive kinetic energy has also been predicted to greatly boost the sensitivity of photosensors. Furthermore, more efficient transport of the photocarriers in the "hot" regime can, in general, improve the efficiency of optoelectronic devices. All of these applications are highly relevant to DoD's interest.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 30, 2022
- Accession Number
- AD1192554
Entities
People
- Bolin Liao
Organizations
- University of California, Santa Barbara