Paper 2D+EM+MN+NS-WeA4
Exploration and Comparison of Optoelectronic Properties of MoS₂ Monolayers with Multilayer Flakes and Mo_xW_1-xS₂ Ternary Compounds

Wednesday, November 1, 2017, 3:20 pm, Room 16

2D transition metal dichalcogenide (TMDC) semiconductors, including MoS₂, WS₂, and more recently ternary compounds, exhibit exceptional structural, electrical and optical properties that make these materials of great interest for nano-optoelectronic devices. For example, unlike graphene, TMDCs have a bandgap, which has the remarkable characteristic of becoming direct when the material is in monolayer form, while it is indirect when the material is composed of multiple layers.

Here, we report the synthesis of monolayer MoS₂, WS₂, ternary Mo_xW_1-xS₂ ternary compounds and MoS₂/WS₂-based heterostructures, by chemical vapor deposition (CVD) process at temperatures in the range 950-1000 C, without the use of seeds to avoid contamination. The material was extensively characterized using micro-Raman spectroscopy, micro-photoluminescence, and electron microscopy.

Using such large area CVD grown materials, large-area MoS₂ photoconductive detector devices were fabricated using conventional photolithography to realize of interdigitated metal fingers. The electrical and spectral photoresponse from monolayer and multilayer MoS₂ have been compared, in terms of responsivity and specific detectivity. The monolayer devices exhibited high photoconductive gain and detectivity near 10¹² Jones, which was also found to be higher than in the case of multilayer MoS₂ devices. The rise and decay time of passivated monolayer devices was investigated and shown to be much faster than the unpassivated devices.