Monolayers of transition metal dichalcogenides (TMDCs) exhibit excellent electronic and optical properties. However, the performance of these two-dimensional (2D) devices are often limited by the large resistance offered by the metal contact interface. Till date, the carrier injection mechanism from metal to 2D TMDC layers remains unclear, with widely varying reports of Schottky barrier height (SBH) and contact resistance ( ), particularly in the monolayer limit. In this work, we use a combination of theory and experiments in Au and Ni contacted monolayer MoS2 device to conclude the following points: (i) the carriers are injected at the source contact through a cascade of two potential barriers -the barrier heights being determined by the degree of interaction between the metal and the TMDC layer; (ii) the conventional Richardson equation becomes invalid due to the multi-dimensional nature of the injection barriers, and using Bardeen-Tersoff theory, we derive the appropriate form of the Richardson equation that describes such composite barrier; (iii) we propose a novel transfer length method (TLM) based SBH extraction methodology, to reliably extract SBH by eliminating any confounding effect of temperature dependent channel resistance variation; (iv) we derive the Landauer limit of the contact resistance achievable in such devices. A comparison of the limits with the experimentally achieved contact resistance reveals plenty of room for technological improvements.

This letter reports the temperature-dependent electrical parameters of Pd/n-ZnO thin film-based Schottky diodes grown on n-Si <100> substrates by thermal evaporation method. The parameters have been investigated by considering a Gaussian distributed barrier height across the Pd/n-ZnO interface with a standard deviation σ 0 around a mean barrier height qφ B,m . As compared with the reported results, the estimated values of the Richardson constant (∼19.54 Acm −2 K −2 ) and mean barrier height (∼1.41 eV) are much closer to their theoretically predicted values of 32 Acm −2 K −2 (for m * e =0.27m 0 ) and 1.42 eV (for work function of Pd = 5.12 eV and electron affinity of ZnO = 3.7 eV), respectively.

Atomically thin semiconductors are of interest for future electronics applications, and much attention has been given to monolayer (1L) sulfides, such as MoS 2 , grown by chemical vapor deposition (CVD). However, reports on the electrical properties of CVD-grown selenides, and MoSe 2 in particular, are scarce. Here, we compare the electrical properties of 1L and bilayer (2L) MoSe 2 grown by CVD and capped by sub-stoichiometric AlO x . The 2L channels exhibit ∼20× lower contact resistance ( R C ) and ∼30× larger current density compared with 1L channels. R C is further reduced by >5× with AlO x capping, which enables improved transistor current density. Overall, 2L AlO x -capped MoSe 2 transistors (with ∼500 nm channel length) achieve improved current density (∼65 μA/μm at V DS = 4 V), a good I on / I off ratio of >10 6 , and an R C of ∼60 kΩ·μm. The weaker performance of 1L devices is due to their sensitivity to processing and ambient. Our results suggest that 2L (or few layers) is preferable to 1L for improved electronic properties in applications that do not require a direct band gap, which is a key finding for future two-dimensional electronics.

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This paper reports the ultraviolet (UV) detection characteristics of Pd/ZnO nanoparticles (NPs) based Schottky diodes grown on Sn coated n-Si substrates by thermal evaporation method. The measured current-voltage characteristics of the Pd/ZnO NPs/Sn/n-Si diodes under both the dark and UV illumination at wavelength of 365 nm have been presented for the applied bias voltage varying from −3 to 3 V. The as-fabricated photodiodes show a high-contrast ratio (i.e., the photocurrent to dark current ratio) of ß541.34, an excellent quantum efficiency of ß68%, a reasonably good responsivity of ß0.20 A/W at 365 nm, and −3 V reverse bias voltage at room temperature.