Spectral photocurrent characteristics in Au-nanostructure-decorated two-dimensional transition-metal dichalcogenides

Abstract

Two-dimensional (2D) van der Waals (vdW) materials have been researched for electronics and optoelectronics in nanomaterials research, due to low dimension and their unique optical and electronic properties. Particularly, 2D transition metal dichalcognides (TMDCs) have been attractive because of distinct singularities near the band edges, direct band-gap in monolayer regime, and valley polarization. Recently, the combination of TMDCs semiconductors and other nanomaterials or 2D TMDC heterojunctions are focused, inducing new types of quantum physics and providing a thin device platform with high performance. Among the combinations, plasmonic nanostructure-2D vdW materials hybrid system have been demonstrated. Surface plasmon resonance of plasmonic nanostructures enhances the electric field enhancement of light and imprisons the light within 2D materials, inducing enhanced absorption in a device. Moreover, it is recently reported that hot electrons excited by surface plasmon resonance of plasmonic nanostructure can enhance the performance and quantum efficiency of semiconductor photodetectors, such as silicon, TiO2, and GaAs. This dissertation mainly concerns Au nanostructure decorated monolayer TMDCs devices. Especially, I focus the photocurrent characteristics by the surface plasmon resonance of Au nanostructure in TMDC monolayer devices. In this dissertation, first investigation is the electrical contact property between monolayer TMDCs and various metals for fabrication of TMDCs phototransistor with high performance. 2D materials have a few dangling bond on the surface and cannot form covalent bond with metal, inducing high contact resistance and low quantum efficiency. Therefore, I examined the top contact resistance in MoS2 devices with various metal electrode by transfer length method (TLM) and confirmed that the best candidate for metal contact in monolayer MoS2 is a titanium (Ti). The next, I observe the sub band-gap photocurrent in gold (Au) Nanorods (NRs) decorated TMDCs semiconductor devices. The sub-band-gap photocurrent originated from plasmon-induced hot electron from Au NRs. Then, the sub-band-gap photocurrent is modulated by the surface plasmon resonance of Au NRs. I demonstrated the photovoltaic response of plasmon-induced hot electron in the TMDCs p-n stack junction devices. Last, I probed chiral photocurrent response in chiral Au nanoparticles decorated TMDCs monolayer semiconductor and p-n stack junction devices. Chiral plasmon resonance of Au nanoparticles induces the differential photocurrent by right- and left-circularly polarized light.