Perpustakaan Digital ITB

Tungsten disulfide is one of monolayer transition metal dichalcogenides, with high on-off ratio, about 108, and wide intrinsic band gap, around 1-2.1 eV, that is missing in graphene. Monolayer transition metal dichalcogenides are semiconductor materials with X-M-X covalently bonded, where M is the transition metal and X stands for chalcogen. We study effect of sample morphology and device processing to its quality by photoluminescence imaging. By use two different methods of Chemical Vapor Deposition, low and ambient pressure Chemical Vapor Deposition, we observed an imperial linkage between the sample quality and different sample morphology. Photoluminescence of whole monolayer sample, has average photoluminescence counts about 2,406, is lower than monolayer in the edge of heterogeneous sample, with average photoluminescence counts about 19,381. In addition, photoluminescence also changed due to device fabrication process, especially in lithography and liquid gating process. It means that doping rate of the sample has already changed. Besides that, we also revealed effect of sample quality on the field effect control of the photoluminescence and subsequent electrical luminescence through back and liquid gating. Photoluminescence value of device was changed due to different gate voltage, both in back gating and liquid gating. Actually, the difference voltage when the device is off (when photoluminescence can be seen) indicates band gap of material. From the result, we can conclude that band gap of tungsten disulfide is about 2.5 eV. Nevertheless, photoluminescence in back gating only scan partially region of liquid gating. In addition, we can only see current shift via liquid gating. It means that ionic liquid can accumulate much more carrier than conventional FET. Based on that, we can summarize that photoluminescence only gives description about doping rate of sample. We hope that our studies can be used as quick approach to predict doping level of device and path to use new physical ingredients into the novel device applications.