ALD Assisted 2D Monolayer Transition Metal Dichalcogenides and Their Applications in Optoelectronics

Recently, 2D Transition Metal Dichalcogenides (TMDCs) have received significant attention in the field of optoelectronics due to their extraordinary optical and electrical properties [1, 2]. Among TMDC family, molybdenum disulfide (MoS2) has intensively been studied. Bulk and monolayer MoS2 have bandgap energy of similar to 1.3 eV and similar to 1.8 eV, respectively [1,3]. Different growth techniques such as Atomic Layer Deposition (ALD) are alternatively used aiming at uniform growth of MoS2. For ALD Mo and S precursors such as Mo(CO)(6), MoCl5 and H2S, dimethyl disulfide respectively are used on SiO2/Si or sapphire substrate [4,7]. Using ALD, the synthesis of wafer scale uniform bilayer MoS2 film has been reported. However, in the experiment, H2S precursor is used both in the reaction cycle [4,5] and high-temperature post-deposition annealing performed as necessary step to reduce impurity contents and increase crystal quality in the films [6,7]. H2S is highly toxic and has a high vapor pressure at room temperature. As a result, it requires a special container pressure controller and gaskets which increase considerably the cost and risk for use in ALD process. For 2D MoS2 growth by ALD, uniformly distributed small-size degrees akes are reported in [4,5]. In order to control the growth process of 2D MoS2, the flake quantity and distribution needs to be taken under control. Interestingly, in CVD, it is possible to grow MoS2 layer using MoO3 thin film instead of powder. The control of MoS2 flake size, density, number of layer and cleanness can be achieved by controlling the MoO3 thin film. Plasma Enhanced Atomic Layer Deposition technique should be most suitable for such a uniform deposition. Successful growth is reported in [8] but it is not optimized for MoS2 growth.