Two-dimensional Transition Metal Dichalcogenide Materials With Vertically Standing Layered Structure For High Performance Photodetector

Recently, transition metal dichalcogenide(TMD) materials, which possess the same layer-stack structure as graphene, have attracted increasing attention due to their excellent mechanical, electrical and optical properties, as well as nonzero band gap. Particularly, molybdenum disul?de(MoS2) and molybdenum diselenide(MoSe2), two typical 2D metal dichalcogenide materials, have been applied into many fields, such as photocatalysis, Li ion battery, photovoltaics and photodetectors. Great progress has been made in the researches on TMD-based devices; however there are still many problems to be solved. On the one hand, it is still a challenge to grow large-area TMD, even in square centimeter scale. On the other hand, the sensitivity and response speed, which are the two key indexes of photodetectors, are required to be further improved for the application of TMD materials in photodetectors. Above all, it is very significant to prepare TMD in a large scale and design TMD-based photodetectors with high performance.In this thesis, we have successfully prepared MoS2 and MoSe2 films with vertically standing layered structure and designed high performance photodetectors based on these two materials. The thesis includes the following sections:(1) Two-dimensional MoS2 and MoSe2 films have been prepared using a sputter system. The crystal quality of the films is further improved by post-annealing method. Large-scaleTMD films can be readily obtained by increasing the sizes of substrate and sputtering target. It is noted that MoS2 and MoSe2 films prepared in this way have avertically standing layered structure.(2) Si/MoS2 heterojunction photodetector has been fabricated by depositing MoS2 films with a vertically standing layered structure on p-type silicon. The Si/MoS2 heterojunction photodetector exhibits a wide spectrum response ranging from visible to NIR light with an extremely high detectivity(~1013 Jones) and a ultra-fast response speed(~3 μs), which represents the best results achieved for MoS2-based photodetectors so far. In addition, the performance degradation of this device is nearly negligible for a long period.(3) A Si/MoSe2 heterojunction photodetector with vertically standing layered structure has been designed using graphene as the transparent electrode. The existence of graphene can improve the quality of the junction and facilitate the collection of electrons. As a result, it can work under the illumianation of a 1 MHz pulsed light and show an extremely high response speed of 270 ns, much quicker than the other conventional photodetectors.