Electronic and optoelectronic devices based on 2d materials

In this thesis, a comprehensive study on 2D materials has been carried out and investigated by various characterization tools. The 2D materials have been grown by in-house CVD system and the growth parameters and configuration have been optimized. Not only individual monolayers, but also their heterostructures, have been obtained and investigated by Raman and Photoluminescence spectroscopy. It has been found that, the PL intensity of MoS2 on top of the graphene is quenched with a factor of 10 due to charge transfer between MoS2 and graphene. In addition, direct growth of MoS2 on top of graphene resulted in nanometer sized flakes and bulky micrometer stacks of MoS2, mainly due to higher density of seeding spots on graphene. Furthermore, the long-term stability of the CVD-grown MoS2 has been investigated. It has been found that higher growth rate due to higher seeding density, results in relatively unstable MoS2 structures under ambient atmosphere conditions. A novel growth configuration with slower growth rate is proposed and the effectiveness of the proposed method has been verified by long-term observations, thermal aging experiments and DFT calculations. Device performance investigations of MoS2 and WS2 have been investigated under identical conditions. The FETs of MoS2 and WS2 show reasonably high current ON/OFF ratios and mobilities of ~104 and ~105 and 1.45 cm2V-1s-1 and 0.98 cm2V-1s-1, respectively. It is found that WS2 shows higher sensitivity to environmental conditions. Furthermore, as a performance enhancement method, the MoS2 phototransistor has been sensitized by colloidal quantum wells and ~11-fold photoresponsivity enhancement has been achieved by increase of absorbance via energy transfer.