  Two-dimensional semiconductors are excellent candidates for next-generation
electronics and optoelec-tronics thanks to their electrical properties and
strong light-matter interaction. To fabricate devices with optimal electrical
properties, it is crucial to have both high-quality semiconducting crystals and
ideal con-tacts at metal-semiconductor interfaces. Thanks to the mechanical
exfoliation of van der Waals crystals, atomically-thin high-quality
single-crystals can easily be obtained in a laboratory. However, conventional
metal deposition techniques can introduce chemical disorder and metal-induced
mid-gap states that induce Fermi level pinning and can degrade the
metal-semiconductor interfaces, resulting in poorly performing devices. In this
article, we explore the electrical contact characteristics of Au-InSe and
graphite-InSe van der Waals contacts, obtained by stacking mechanically
exfoliated InSe flakes onto pre-patterned Au or graphite electrodes without the
need of lithography or metal deposition. The high quality of the
metal-semiconductor interfaces obtained by van der Waals contact allows to
fabricate high-quality Schottky di-odes based on the Au-InSe Schottky barrier.
Our experimental observation indicates that the contact barrier at the
graphite-InSe interface is negligible due to the similar electron affinity of
InSe and graphite, while the Au-InSe interfaces are dominated by a large
Schottky barrier.
