MULTIPHOTON ABSORPTION IN MONOLAYER TRANSITION METAL DICHALCOGENIDES

Abstract

Identifying light absorption mechanisms in nanoscale materials, which are more efficient than those observed in bulk semiconductors, are of paramount importance to next-generation, infrared photo-detection. In this thesis, degenerate two-photon absorption (2PA) and three-photon absorption (3PA) with two-dimensional (2D) excitonic effects are studied in single-layer molybdenum disulfide (1L-MoS2). Both 2PA and 3PA coefficients of 1L-MoS2 are theoretically predicted to be enhanced by 10-1000 times in the near-infrared (NIR), as compared with those of bulk semiconductors. The theoretical prediction is validated by measuring photocurrents induced by 2PA or 3PA in a 1L-MoS2 photo-detector at room temperature. Theoretical model is also developed to calculate 2PA spectra of other monolayer transition metal dichalcogenides and it reveals the intrinsic nature of 2PA process by comparing the calculated α2-values with experimental data. Our finding lays theoretical foundation and provides experimental evidence for developing sensitive infrared multiphoton detectors for nano-photonics.