Tuning the optical properties of molybdenum oxide using electric field: A theoretical and experimental study

Molybdenum Oxide (MoO₃) with van der Waals structure can lead to the exotic properties under the action of external physical perturbation. Here, a combined density functional theory and an experimental study were performed to analyze the response of MoO₃ under electric field. The electric field with the strength varying from 0.05 V/Å to 0.23 V/Å was applied across the MoO₃ cell which induced the splitting in the valence and conduction band and decreases the bandgap. A critical electric field of 0.23 V/Å resulted a closing of the bandgap of MoO₃ and led semiconductor to metal transition. The results of DFT regarding decrease in the bandgap of MoO₃ were further supported experimentally. For this, MoO₃ films were fabricated using thermal evaporation and their chemical and optical properties were analyzed using X-ray photoelectron spectroscopy and Electroreflectance (ER). To analyze the optical response, an ER analysis with external voltage varying from 10 to 50 volts was performed on Aluminum/MoO₃/Aluminum heterostructure. The resultant ER spectra revealed three distinct critical points that correspond to the fundamental as well as defect related optical transitions involved in MoO₃. The Third derivative functional form model applied on the ER spectra depicted a monotonical decrease in the critical points of MoO₃ at lower voltage. At high voltage of about 80 volts, the existence of high built-in electric field results the delocalization in the electrons and hole wave function and gives rise to the Franz-Keldysh oscillations.