Colloidal Molybdenum Diselenide Nanocrystals for Tunable, Broadband, and Mixed-Dimensional Photodetectors

Two-dimensional (2D) semiconductors with a direct band gap are attractive for the fabrication of 2D/Si heterostructures for complementary metal–oxide–semiconductor compatible nanophotonic devices. We report the characteristics of sonochemically exfoliated molybdenum diselenide (MoSe2) nanocrystals (NCs) integrated on large-area Si platforms to demonstrate tunable and broadband heterojunction photodetectors. The exfoliation of bulk materials to the 2H-semiconducting phase of MoSe2 NCs exhibiting excitonic absorption peaks with characteristic 2D nature is established. A gradual blue shift in the absorption peaks accompanied by the stiffening of A1g Raman mode supports the size-dependent properties of NCs. Spectral response of MoSe2-NCs/Si (2D/3D) heterojunction devices reveal size-tunable and broadband (400–1400 nm) photoresponse, with the optimum sample (size ∼12 nm) showing a peak responsivity and a detectivity of ∼960 mA/W and ∼1.8 × 1012 Jones, respectively, at a low bias (−2 V).