Abstract

Layered molybdenum disulfide (MoS2) is emerging as a promising candidate for novel electronic applications, though the focus has largely been on few-layered thin films and in-layer electrical properties. MoS2 shows various nontrivial departures in its electrical properties in comparison to isotropic crystalline materials, however the understanding of anisotropic properties, particularly of charge carrier mobility in MoS2 flakes, is meagre. We experimentally study inter-layer mobility in mechanically exfoliated MoS2 flakes. The choice of a suitable sandwich device structure enables us to study the inter-layer transport using temperature dependent current–voltage (J–V) and impedance spectroscopy. The separation of peaks in the imaginary part of impedance i.e. Im (Z) spectra due to defects and transport in the space charge limited regime allows measurement of mobility un-encumbered by other effects. We study flakes obtained from both naturally occurring and synthetic crystals. The calculated inter-layer mobility ( μ⊥ ) exhibits μ⊥∼Tδ temperature dependence with δ = 1.6 and thereby revealing that impurity scattering is the dominant mechanism. A further confirmation that the mobility is limited by charged impurity scattering comes from the observation that it improves for temperatures lower than a characteristic temperature, which marks deionization of donor impurities. Our results provide a direct estimation of the inter-layer mobility in exfoliated MoS2 flakes and would lead to carrier transport engineering and design strategies for applications based on MoS2 flakes.