Abstract-Unconventional Terahertz Carrier Relaxation in Graphene Oxide: Observation of Enhanced Auger Recombination due to Defect Saturation

Jaeseok Kim , Juyeong Oh , Chihun In , Yun-Shik Lee , Theodore B. Norris , Seong Chan Jun , and Hyunyong Choi

http://pubs.acs.org/doi/abs/10.1021/nn406066f

ACS Nano, Just Accepted Manuscript

DOI: 10.1021/nn406066f

Publication Date (Web): February 4, 2014

Copyright © 2014 American Chemical Society

Photoexcited carrier relaxation is a recurring topic in understanding the transient conductivity dynamics of graphene-based devices. For atomically-thin graphene oxide (GO), a simple free-carrier Drude response is expected to govern the terahertz (THz) conductivity dynamics ―same dynamics observed in conventional CVD-grown graphene. However, to date no experimental testimony has been provided on the origin of photo-induced conductivity increase in GO. Here, using ultrafast terahertz (THz) spectroscopy, we show that the photoexcited carrier relaxation in GO exhibits a peculiar non-Drude behavior. Unlike graphene, the THz dynamics of GO show percolation behaviors: as the annealing temperature increases, transient THz conductivity rapidly increases and the associated carrier relaxation changes from mono- to bi-exponential decay. After saturating the recombination decay through defect trapping, a new ultrafast decay channel characterized by multi-particle Auger scattering is observed whose threshold pump fluence is found to be 50 µJ/cm2. The increased conductivity is rapidly suppressed within 1 ps due to the Auger recombination, and non-Drude THz absorptions are subsequently emerged as a result of the defect-trapped high-frequency oscillators.