Two-photon absorption and subband photodetection in monolayer MoS.

We develop a theoretical model to quantify the two-photon absorption (2 PA) coefficients of monolayer MoS. Based on two-dimensional excitons, our model reveals the 2 PA coefficient spectrum on the order of 0.01-0.1 cm/MW in the near-infrared for monolayer MoS. As compared to the band theory for bulk semiconductors, these coefficients are enhanced by at least one order of magnitude. Our model is in agreement with light-intensity-dependent photocurrent measurements on a monolayer MoS, subband photodetector with femtosecond laser pulses.