Contact Properties of Two-Dimensional Ferroelectric α-In2Se3

The performance of two-dimensional (2D) material devices is strongly affected by the properties of the contacts. A good understanding of the contact behavior is vitally important for building high-performance devices. In this work, through studying the properties of field-effect transistors, the Schottky barrier heights (SBHs) at the contacts between the ferroelectric alpha-In2Se3 nanosheet and metals are extracted. Three typical metals with various work functions, titanium (Ti), chromium (Cr), and palladium (Pd), are used as the source/drain electrodes. All the three types of devices show an n-type fieldeffect character despite the large difference of the metal work function (0.8 eV between Pd and Ti). SBHs are measured to be 52 meV for the Pd contact and 24 meV for the Cr contact, while Ti forms an Ohmic contact with alpha-In2Se3 nanosheets. The results suggest a significant Fermi-level pinning near the bottom of the conductive band of alpha-In2Se3. Using the transfer length method (TLM), we find that the contact resistance increases significantly (from 48 k Omega center dot mu m to 4.03 M Omega center dot mu m for the Ti contact and from 288 k Omega center dot mu m to 7.10 M Omega center dot mu m for the Pd contact) as the In2Se3 thickness decreases from 56 nm to about 20 nm for both the Pd and Ti contacts, while the contact resistance for the Pd contact is several times larger than that for the Ti contact. These results are significant to understand the contact properties of 2D ferroelectric materials and provide a strong foundation for the application of alpha-In2Se3 in nanodevices.