We fabricate a vertical thin-film barristor device consisting of highly doped silicon (gate), 300 nm SiO2 (gate dielectric), monolayer graphene, pentacene, and a gold top electrode. We show that the current across the device is modulated by the Fermi
energy level of graphene, tuned with an external gate voltage. We interpret the device current within the thermionic emission theory, showing a modulation of the energy barrier between graphene and pentacene as large as 300meV.
A scheme is proposed to electrically measure the spin-momentum coupling in the topological insulator surface state by injection of spin polarized electrons from silicon. As a first approach, devices were fabricated consisting of thin (<100nm) exfolia
ted crystals of Bi2Se3 on n-type silicon with independent electrical contacts to silicon and Bi2Se3. Analysis of the temperature dependence of thermionic emission in reverse bias indicates a barrier height of 0.34 eV at the Si-Bi2Se3 interface. This robust Schottky barrier opens the possibility of novel device designs based on sub-band gap internal photoemission from Bi2Se3 into Si.
We investigate conductance fluctuations as a function of carrier density $n$ and magnetic field in diffusive mesoscopic samples made from monolayer and bilayer graphene. We show that the fluctuations correlation energy and field, which are functions
of the diffusion coefficient, have fundamentally different variations with $n$, illustrating the contrast between massive and massless carriers. The field dependent fluctuations are nearly independent of $n$, but the $n$-dependent fluctuations are not universal and are largest at the charge neutrality point. We also measure the second order conductance fluctuations (mesoscopic rectification). Its field asymmetry, due to electron-electron interaction, decays with conductance, as predicted for diffusive systems.
Both transport $tau_{tr}$ and elastic scattering times $tau_{e}$ are experimentally determined from the carrier density dependence of the magnetoconductance of monolayer and bilayer graphene. Both times and their dependences in carrier density are fo
und to be very different in the monolayer and the bilayer. However their ratio $tau_{tr}/tau_{e} $is found to be of the order of $1.5 $ in both systems and independent of the carrier density. These measurements give insight on the nature (neutral or charged) and spatial extent of the scattering centers. Comparison with theoretical predictions yields that the main scattering mechanism in our graphene samples could be due to strong scatterers of short range, inducing resonant scattering, a likely candidate being vacancies.
