Comparative Study on Electronic Structures of Sc and Ti Contacts with Monolayer and Multilayer MoS2

Understanding the nature of the contacts in devices based on MoS₂ with metal electrodes is vital to enhancing carrier injection efficiency. In this work, geometric and electronic structures of Sc and Ti contacts with MoS₂ have been comparatively studied by first-principles calculations. The analyses of geometric parameters, charge density distributions, and density of states for the Sc and Ti top contacts with monolayer MoS₂ (mMoS₂) indicate that the interface bonding results in the localization of 4d states of Mo atoms and the consequent metallization of mMoS₂. Therefore, the Sc and Ti top contacts with mMoS₂ are Ohmic, and electron injections via these contacts are efficient. Because of the formations of the metalized Sc–mMoS₂ and Ti–mMoS₂ complexes, in the Sc and Ti top contacts with multilayer MoS₂, Schottky interfaces may be formed in two contact regions. One is in the edge contacts of the Sc–mMoS₂ and Ti–mMoS₂ complexes with mMoS₂ in the channel region in which Schottky barrier heights of 0.11 and 0.39 eV are extracted, respectively. The other is in the top contacts of these two complexes with mMoS₂ under the contacts in which Schottky barrier heights of 0.15 and 0.34 eV are obtained, respectively. Moreover, as the layer number of MoS₂ increases in the top contacts, the Schottky barrier heights show decreasing trends. These trends can be understood on the basis of the changes of electron affinity of multilayer MoS₂. According to the present results, the device based on MoS₂ with Sc electrodes should have better electron injection efficiency and stronger back-gated manipulation of current than the one with Ti electrodes. Furthermore, the electron injection efficiency can be enhanced by using multilayer MoS₂. These predictions are generally consistent with recent experimental observations and provide a delicate understanding of the contacts in these devices.