The impact of electrical contacts on the optical properties of a MoS$_{2}$ monolayer

Achieving high performance in transition-metal-dichalcogenide-based optoelectronic devices is challenging -- the realization of an efficient electrical contacting scheme should not be obtained at the expense of their optical quality. Here we present the optical properties of MoS$_{2}$ monolayers which have been electrically contacted with bismuth and gold. The photoluminescence (PL) spectrum of the samples contacted with both materials is significantly broadened. In the case of the bismuth contacted sample we note an additional, low energy band in the PL spectrum, attributed to a defect state formed during the evaporation of Bi. Comparing the intensity of the excitonic peak and of the defect-related peak, we note that there is a correlation between the type of contacts and the optical properties.