UC Riverside

The successful exfoliation of graphene and studies into its unique electrical and thermal properties has motivated searches for other quasi two-dimensional (2D) materials with interesting properties. The layered van der Waals materials can be cleaved mechanically or exfoliated chemically by breaking the relatively weak bonds that exist between the layers. In this dissertation I focused my research on a special group of inorganic van der Waals materials – layered transition metal dichalcogenides (MX2, where M=Mo, W, Nb, Ta or Ti and X=S, Se or Te). The focus of the investigation was on the low-frequency noise properties of thin films of MoS2 concentrating on the contributions from the channel and the contacts. I describe the process of fabrication, electrical testing and measuring the low-frequency 1/f noise in fabricated three-terminal devices with the MoS2 thin-film channels (f is the frequency). Analysis of the experimental data allowed us to distinguish and separate the channel and contact noise contributions for both as fabricated and aged devices. The noise characteristics of our MoS2–Ti/Au devices are in agreement with the McWhorter model description. This is contrary to what was observed in graphene devices, where the noise spectral density follows the mobility fluctuation model. The trap density extracted from the noise measurements is on the order of 2 x 1019 eV-1cm-3 and 2.5 x 1020 eV-1cm-3 for as fabricated and aged samples, respectively. These values are of the same order of magnitude as those in high-k MOSFETS investigated in the past. These results of this dissertation research may lead to new applications of van der Waals materials and new methods of noise reduction during fabrication and design of devices made from these materials.