Tuning the Electrical and Optical Properties of MoS$_2$ under High Pressure

Transition metal dichalcogenides (TMDCs), such as molybdenum disulfide (MoS$_2$), has been of recent interest to many theoretical and experimental studies. MoS$_2$ has served as a potential material for optoelectronic and field-effect-transistors (FETs) with high on/off ratios (up to 10$^8$). MoS$_2$ is composed of quasi-two-dimensional sheets that are stacked on top of one another where each monolayer is tri-layered with a transition metal, molybdenum, in the middle that is covalently bonded to a chalcogen atom, sulfur, located on the top and bottom of the layers. These layers are separated by weak van der Waals (vdW) forces along the c-axis which makes the properties of MoS$_2$ anisotropic. Having control over the electronic properties, and therefore, the band-gap of MoS$_2$, allows for a wide range of applications from electrochemical devices to tunable photo-detectors to be adopted. We demonstrate the electronic phase transition of MoS$_2$ from semiconducting to a metallic state at $\sim$15GPa. The electronic transport properties in the semiconducting region (lower pressures) exhibits a shockley-like behavior while in the metallic region (higher pressures), we observe ohmic transport. We also examine the light-induced electronic properties by creating optical switches under pressure in greater detail. This photo-current behavior of MoS$_2$ allows for optical switches with three order decrease in turn-on time. We examine the change in the activation energy, optical Raman, XRD, and resistance, by inducing pressure to MoS$_2$ up to 35 GPa.