Growth and Optoelectronic Properties of Large-Scale Monolayer MoS2
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In this Dissertation we describe two different methods for growing large area continuous monolayer MoS 2 . Our growth process is followed by characterization of the grown film by using different characterization methods such as optical microscope, Scanning Electron Microscopy (SEM), Raman, photoluminescence (PL), Atomic Force Microscopy (AFM), and optoelectronic measurements. Chemical Vapor Deposition (CVD) Method: In this method we were able to grow large area discrete as well as continuous (1 cm) monolayer MoS 2 at ambient pressure. A systematic study was performed on the growth of monolayers of MoS 2 . Sulfur Vapor Transport Method (SVT) Method: In this method, we were also able to grow large area discrete monolayers and continuous (>1 cm) monolayer MoS 2 at ambient pressure. In our approach, first we have deposited an ultrathin film of MoO 3 by E-beam evaporator. The pre-deposited film then was sulfurized in the CVD chamber. Studies on the thickness of the pre-deposited film (5 Å- 1.9 Å), reaction time (1min-10min) was systematically carried out. One of the main achievements in this approach was in-situ patterning of the large area continuous monolayer (ML) and bilayer (BL) MoS 2 . We were able to transfer monolayer MoS 2 onto any arbitrary substrate by using Polymethyl methacrylate (PMMA) and wet etching method. Our approach is scalable and can be used for the mass production of the large area monolayer MoS 2 . Optoelectronic Measurements: We have studied the optoelectronic properties of the large area (∼ 4 mm) ML MoS 2 . Phototransistor fabricated in our lab shows very high sensitivity to the incident light. Power dependence (60 mW-150 mW), temperature dependence (100 K-300 K), and bias voltage dependence (5 V-50 V) were systematically studied. Our device has the potential to be used in a wide range of fast and highly sensitive photodectors.