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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.