Approaching the Schottky–Mott limit in van der Waals metal–semiconductor junctions

Abstract

The junctions formed at the contact between metallic electrodes and semiconductor materials are crucial components of electronic and optoelectronic devices . Metal-semiconductor junctions are characterized by an energy barrier known as the Schottky barrier, whose height can, in the ideal case, be predicted by the Schottky-Mott rule on the basis of the relative alignment of energy levels. Such ideal physics has rarely been experimentally realized, however, because of the inevitable chemical disorder and Fermi-level pinning at typical metal-semiconductor interfaces. Here we report the creation of van der Waals metal-semiconductor junctions in which atomically flat metal thin films are laminated onto two-dimensional semiconductors without direct chemical bonding, creating an interface that is essentially free from chemical disorder and Fermi-level pinning. The Schottky barrier height, which approaches the Schottky-Mott limit, is dictated by the work function of the metal and is thus highly tunable. By transferring metal films (silver or platinum) with a work function that matches the conduction band or valence band edges of molybdenum sulfide, we achieve transistors with a two-terminal electron mobility at room temperature of 260 centimetres squared per volt per second and a hole mobility of 175 centimetres squared per volt per second. Furthermore, by using asymmetric contact pairs with different work functions, we demonstrate a silver/molybdenum sulfide/platinum photodiode with an open-circuit voltage of 1.02 volts. Our study not only experimentally validates the fundamental limit of ideal metal-semiconductor junctions but also defines a highly efficient and damage-free strategy for metal integration that could be used in high-performance electronics and optoelectronics.

Van der Waals Contact to 2D Semiconductors with a Switchable Electric Dipole: Achieving Both n‐ and p‐Type Ohmic Contacts to Metals with a Wide Range of Work Functions

“…Most importantly, bilayer pS contacting to medium‐WF Mo 2 CF 2 can form both n‐ and p‐type SB‐free contacts using the same pS by switching its built‐in electric dipole, and, metallic Mo 2 CF 2 partially screen the cross‐plane dipole in pS resulting in tunable bandgap. Our findings for MpSJ, that is, both n‐ and p‐type SB‐free contacts can be obtained with the same pS contacting to metals with a wide range of work‐functions (which is not limited to extremely low or high metal work‐function as reported in literature),40,46 are essential for high‐performance optoelectronic devices49 and complementary metal‐oxide‐semiconductor (CMOS) logic circuitry 50…”

Physics and Optoelectronic Simulation of Photodetectors Based on 2D Materials

“…Figure b displays the output characteristics of the device, which are basically consistent with those of a metal–oxide–semiconductor field‐effect transistor (MOSFET) in terms of typical cutoff, variable resistance, and saturation regions, indicating the reliability of our numerical phototransistor simulation . Figure c,d presents the relationship between the output current ( I d ) and V d for different V g in light ( P 0 = 1 nW) and dark environments, respectively.…”

Strain Improving the Performance of a Flexible Monolayer MoS2 Photodetector

“…The surface potential distribution of a monolayer MoS 2 without applied strain is homogeneous. [39] The Schottky barrier's height on both sides are almost identical without the strain, and is as shown in Figure 5a. A potential difference is produced in the internal monolayer MoS 2 along the armchair direction under the 0.8% strain, while there is no potential difference produced in the zigzag direction.…”