Bandgap engineering of monolayer molybdenum disulfide by oxygen plasma

• Main Author: Thwe, Aye Sandar.
• Other Authors: Tay Beng Kang
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/55107
• Institution: Nanyang Technological University

Monolayer Molybdenum Disulfide (MoS2) has been a favourable candidate for next generation high performance semiconducting devices due to the presence of a direct bandgap. Bandgap engineering of monolayer MoS2 could lead to many new applications and functionalities in the field of optoelectronics by controlling its optical and electrical properties. In this project, the direct bandgap of the monolayer MoS2 is tuned via oxygen plasma treatment for varying periods of time. For comparative studies, the pristine MoS2 samples were prepared by micromechanical cleavage and characterized by optical microscopy, Raman spectroscopy, Atomic Force Microscopy and Photoluminescence spectroscopy. The effect of oxygen plasma on the monolayer MoS2 was observed by comparing the photoluminescence spectra of pristine and oxygen-treated MoS2. Results from the photoluminescence measurements have shown that the photoluminescence intensity reduces and the photoluminescence peaks (A1 and B1) red-shifted with longer duration of oxygen plasma treatment. This might be due to the direct-to-indirect bandgap transition and the reduction in bandgap energy, possibly resulting from the substitution of oxygen atoms in the place of sulphur atoms in S-Mo-S structures. This hypothesis also agrees with the Density Function Theory (DFT) simulation used to calculate the electronic band structure of 2x2 MoS2 unit cell with an oxygen atom replaced in the place of a sulphur atom.