Band Offset and Electron Affinity of Monolayer MoSe₂ by Internal Photoemission

The electron energy band alignment of the monolayer MoSe₂/oxide/Si system is characterized by internal photoemission spectroscopy, where the oxide is Al₂O₃ or SiO₂. Raman and photoluminescence spectroscopic measurements confirm the high quality of monolayer MoSe₂ exfoliated with gold film as medium. At the oxide flat-band condition, the band offset from the monolayer MoSe₂ valence band maximum to the Al₂O₃ and SiO₂ conduction band minimum are measured to be (4.10 ± 0.05) eV and (4.80 ± 0.05) eV, respectively. By referencing the recently reported band gap value of 2.18 eV for monolayer MoSe₂, we obtain the electron affinity of monolayer MoSe₂ to be (3.8 ± 0.1) eV on Al₂O₃/Si and (3.5 ± 0.1) eV on SiO₂/Si. It is believed that the results from this study will help accelerate the design of electronic and optoelectronic devices that employ this class of two-dimensional materials.