Caffeine-driven n-type doping in multilayer MoS2 field effect transistor

Abstract

It has been reported that the electrical characteristics of molybdenum disulfide field effect transistors can be customized through the chemical integration of mechanically exfoliated multilayer MoS₂ by caffeine. The device was completely submerged in the caffeine solution for 15 s, dried with a N₂ cannon, and its electrical characteristics were assessed. Caffeine causes n-doping in the multilayer MoS₂, as confirmed by transfer characteristics, Raman spectroscopic analysis and X-ray Photoelectron Spectroscopy. After the doping procedure, the threshold voltage moved to the left, and the electrical property increased at room temperature outside without causing any damage to the device. The Raman spectrum's downward trend in peak shifting of the E_{2 g} and A_{1 g} peaks following the functionalization of caffeine molecules shows an increase in electron concentration on the MoS₂ surface. In comparison to the pristine device, the extracted field effect mobility increased by a factor of 5.5. Compared to the pristine device (4.6 V/decade), the subthreshold swing was decreased to 1.6 V/decade. After doping, the device was annealed for 15 min at 90 °C, which brought it very near to being immaculate. Additionally, the n-type doping by caffeine was shown by X-ray Photoelectron Spectroscopy analysis. The MoS₂ surface exhibited caffeine adsorption, as demonstrated by the Time-of-Flight Secondary Ionization Mass Spectrometry measurement.