Vertical graphene-based device concepts that rely on quantum mechanical tunneling are intensely being discussed in the literature for applications in electronics and optoelectronics. In this work, the carrier transport mechanisms in semiconductor-insulator-graphene (SIG) capacitors are investigated with respect to their suitability as electron emitters in vertical graphene base transistors (GBTs). Several dielectric materials as tunnel barriers are compared, including dielectric double layers. Using bilayer dielectrics, we experimentally demonstrate significant improvements in the electron injection current by promoting Fowler-Nordheim tunneling (FNT) and step tunneling (ST) while suppressing defect mediated carrier transport. High injected tunneling current densities approaching 10(3) A cm(-2) (limited by series resistance), and excellent current-voltage nonlinearity and asymmetry are achieved using a 1 nm thick high quality dielectric, thulium silicate (TmSiO), as the first insulator layer, and titanium dioxide (TiO2) as a high electron affinity second layer insulator. We also confirm the feasibility and effectiveness of our approach in a full GBT structure which shows dramatic improvement in the collector on-state current density with respect to the previously reported GBTs. The device design and the fabrication scheme have been selected with future CMOS process compatibility in mind. This work proposes a bilayer tunnel barrier approach as a promising candidate to be used in high performance vertical graphene-based tunneling devices.

Electronic and dielectric properties of vapor-phase grown MoS2 have been investigated in metal/MoS2/silicon capacitor structures by capacitance–voltage and conductance-voltage techniques. Analytical methods confirm the MoS2 layered structure, the presence of interfacial silicon oxide (SiOx) and the composition of the films. Electrical characteristics in combination with theoretical considerations quantify the concentration of electron states at the interface between Si and a 2.5–3 nm thick silicon oxide interlayer between Si and MoS2. Measurements under electric field stress indicate the existence of mobile ions in MoS2 that interact with interface states. On the basis of time-of-flight secondary ion mass spectrometry, we propose OH– ions as probable candidates responsible for the observations. The dielectric constant of the vapor-phase grown MoS2 extracted from CV measurements at 100 kHz is 2.6 to 2.9. The present study advances the understanding of defects and interface states in MoS2. It also indicates opportunities for ion-based plasticity in 2D material devices for neuromorphic computing applications.

Non‐volatile resistive switching is demonstrated in memristors with nanocrystalline molybdenum disulfide (MoS2) as the active material. The vertical heterostructures consist of silicon (Si), vertically aligned MoS2, and chrome/gold metal electrodes. Electrical characterizations reveal a bipolar and forming‐free switching process with stable retention for at least 2500 s. Controlled experiments carried out in ambient and vacuum conditions suggest that the observed resistive switching is based on hydroxyl ions (OH−). These originate from catalytic splitting of adsorbed water molecules by MoS2. Experimental results in combination with analytical simulations further suggest that electric field driven movement of the mobile OH− ions along the vertical MoS2 layers influences the energy barrier at the Si/MoS2 interface. The scalable and semiconductor production compatible device fabrication process used in this work offers the opportunity to integrate such memristors into existing Si technology for future neuromorphic applications. The observed ion‐based plasticity may be exploited in ionic‐electronic devices based on transition metal dichalcogenides and other 2D materials for memristive applications.

This paper reviews the experimental and theoretical state of the art in ballistic hot electron transistors that utilize two-dimensional base contacts made from graphene, i.e. graphene base transistors (GBTs). Early performance predictions that indicated potential for THz operation still hold true today, even with improved models that take non-idealities into account. Experimental results clearly demonstrate the basic functionality, with on/off current switching over several orders of magnitude, but further developments are required to exploit the full potential of the GBT device family. In particular, interfaces between graphene and semiconductors or dielectrics are far from perfect and thus limit experimental device integrity, reliability and performance