Improving Electric Contacts to Two-Dimensional Semiconductors

High Number of Transport Modes: A Requirement for Contact Resistance Reduction to Atomically Thin Semiconductors

“…5 shows the model and TCAD simulation calculation of R C for various vdW gap widths, showing the generalization of both the model and simulation. Note that due to software limitations, the TCAD R C computation uses parabolic band structure and density of states (DOS), instead of the 1L MoS 2 DOS calculated by Suryavanshi et al [19]. When calculating the R C heat map using our model with parabolic bands, mirroring the TCAD simulation, we observe similar trends; however, the absolute values of R C are marginally larger when parabolic bands are used.…”

“…As n increases, the conduction band edge approaches the 2-D semiconductor Fermi level and becomes lower relative to the metal Fermi level. As presented by Suryavanshi et al [19], the number of transport modes monotonically increases for energy states above the conduction band edge. Therefore, increasing n allows the metal to inject electrons into relatively higher energy states with respect to the semiconductor conduction band edge, which are associated with larger number of transport modes.…”

“…The resulting current for E < φ B (i.e., tunneling through the barrier) is dominated by field emission and thermionic field emission, and for E > φ B , the resulting current is dominated by thermionic emission. We calculate M(E) by counting the number of modes along the transport direction in the first Brillouin zone, as previously shown by Suryavanshi et al [19]. The subtraction of the Fermi-Dirac distributions ensures that the number of electrons participating in the conduction is determined exclusively by V C [16].…”

“…where L vdW is the vdW gap width, m e is the electron effective mass, and χ 2D is the 2-D material electron affinity, which acts as the vdW gap height. We used a 3-Å-wide gap for our calculation to coincide with previous work [19] resulting in T vdW = 1%-2%; however, various MoS 2 -metal bond lengths have previously been reported [22]. By adjusting for the correct vdW gap width, the model can be generalized for any atomically thin semiconductor-metal contact.…”

Hysteresis-Free Contact Doping for High-Performance Two-Dimensional Electronics

“…However, this approach cannot be used for monolayer 2D materials because the energetic ions damage the fragile materials. − Substitutional doping , can only be achieved at high temperatures through conventional chemical vapor deposition (CVD), which limits this kind of doping to the contact region. Many studies have transferred the heavily doped 2D layer onto the undoped 2D layer to reduce the contact resistance and control the carrier type. , However, processes requiring multiple transfers are impractical, and the van der Waals gap between two 2D layers limits the ultimate contact resistance . As for surface charge transfer doping with doping molecules − or layers, − the nonconductive dopant in the contact region blocks the transport path and causes the degradation of the device performance.…”