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This paper is a contribution to the joint Physical Review Applied and Physical Review Materials collection titled Two-Dimensional Materials and Devices.One-dimensional (1D) edge contacts to two-dimensional (2D) transition-metal dichalcogenides (TMDs), which offer unique features in the design of electronic devices, have recently gained attention. However, the physics of the Schottky barrier of the edge contacts and how exactly it differs from conventional top contacts is not well known. This paper presents a comprehensive ab initio densityfunctional-theory nonequilibrium green's function study of the electrical properties of edge contacts to 2D MoS 2 . It is observed that, due to the intrinsic terminated edge states, 1D edge contacts to MoS 2 are pinned more strongly to a charge-neutrality level that lies closer to the valence band and yields p-type characteristics, which are in contrast to top contacts. This Schottky-barrier anisotropy allows edge contacts in MoS 2 to outperform top contacts in p-type conduction, despite their atomically thin one-dimensional interfaces. Furthermore, the lower limits of contact resistance achievable by edge contacts to MoS 2 are estimated. The role of doping, different edge terminations, and Schottky-barrier inhomogeneity in imperfect edge or hybrid contacts are analyzed to assess and provide design guidelines and conditions under which we can utilize edge contacts for various applications including complimentary field-effect transistor (FET) operation.

As an approximation to the quantum state of solids, the band theory, developed nearly seven decades ago, fostered the advance of modern integrated solid‐state electronics, one of the most successful technologies in the history of human civilization. Nonetheless, their rapidly growing energy consumption and accompanied environmental issues call for more energy‐efficient electronics and optoelectronics, which necessitate the exploration of more advanced quantum mechanical effects, such as band‐to‐band tunneling, spin–orbit coupling, spin–valley locking, and quantum entanglement. The emerging 2D layered materials, featured by their exotic electrical, magnetic, optical, and structural properties, provide a revolutionary low‐dimensional and manufacture‐friendly platform (and many more opportunities) to implement these quantum‐engineered devices, compared to the traditional electronic materials system. Here, the progress in quantum‐engineered devices is reviewed and the opportunities/challenges of exploiting 2D materials are analyzed to highlight their unique quantum properties that enable novel energy‐efficient devices, and useful insights to quantum device engineers and 2D‐material scientists are provided.

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A fully analytical surface potential and current-voltage model is presented for the first time for both lateral homojunction (HMJ) and heterojunction (HTJ) tunneling-field-effect transistors (TFETs) based on 2-D semiconducting channel materials. The dynamic gatemodulated electrostatic potential at the source/channel tunneling junction is suitably captured by solving a quasi-2-D Poisson's equation in both source and channel. Subsequently, the band-to-band tunneling current is accurately derived starting from the Landauer's equation by integrating over all possible carrier energies (or wavevectors) over which tunneling is possible. The model employs Fermi-Dirac statistics in both the degenerate source and drain to compute the surface potential and net current, which yields more physical results than the commonly employed Boltzmann statistics. Its use in Landauer's approach for evaluating the net ON-current leads to an analytical model of the TFET, which physically guarantees zero drain current at zero drain-source bias. Input and output characteristics for both HMJ and HTJ TFETs are computed and compared against rigorous nonequilibrium Green's function (NEGF) simulations for different device parameters to prove the veracity of the model, and the match has been found to be excellent up to ultrashort channel length of 5 nm. Index Terms-2-D materials, 2-D semiconductors, bandto-band tunneling, compact modeling, heterojunction (HTJ), low-power, nonequilibrium Green's function (NEGF), quantum device, steep-slope transistor, tunneling field-effect transistor (TFET), van der Waals heterostructures.