Optical and electrical characterizations of volatile doping effect originated from bilayer photoresist process in MoS2 field-effect transistors

Abstract

Among two-dimensional (2D) van der Waals semiconductors, transition metal dichalcogenide (TMDs) monolayers with atomically thin thicknesses have attracted attention because of their merits for electronic and photonic applications. In contrast to bulk materials, monolayer 2D semiconducting materials have versatile tunability of physical properties, including electrical doping which can be easily modulated by chemical treatments and environmental conditions. Owing to these characteristics, unwanted changes in semiconductor properties are often observed during device fabrication processes using photolithography techniques because of the use of various organic chemicals. In this study, we investigate the volatile doping effects of monolayer MoS2 field-effect transistors fabricated by photolithography using a bilayer photoresist. Each step in the fabrication process was investigated by optical, topographical, and electrical characterization. Consequently, we observed that the poly-dimethyl-glutarimide for the undercut layer and its remover of TP-7000 solution prominently induced n-doping of MoS2, where the effect in TP-7000 was more prominent. This doping effect was drastically reduced through the post-annealing process. Our results indicate that the photolithography process using bilayer PR causes a volatile n-doping effect in the fabrication of devices based on TMD monolayers.