posted on 2021-04-16, 18:34authored byJon K. Gustafson, Daniel Wines, Ellen Gulian, Can Ataca, L. Michael Hayden
We
investigate the effect of molecular oxygen on the photoconductivity
of monolayer MoS2 via broad-band time-resolved terahertz
spectroscopy. We observe that the photoconductivity of monolayer MoS2 transitions from negative to positive when the environment
of MoS2 changes from vacuum to atmospheric pressure. We
argue that this transition from negative to positive photoconductivity
results from physically adsorbed oxygen depleting excess electrons
from the n-type MoS2. We attribute the negative photoconductivity
to negative trion formation, in which photoinduced excitons capture
excess electrons from MoS2. We attribute the positive photoconductivity
to negative trion formation as well; however, in this case, photoinduced
excitons capture photoinduced defect electrons rather than excess
electrons, which have been immobilized by physisorbed oxygen. These
results should prove useful to those who look to make sensors and
other types of devices out of monolayer MoS2 as physisorbed
gases, particularly oxygen, can dramatically affect the conductivity
of the monolayer.