We demonstrate tunable Schottky barrier height and record photo-responsivity in a new-concept device made of a single-layer CVD graphene transferred onto a matrix of nanotips patterned on n-type Si wafer. The original layout, where nano-sized graphene/Si heterojunctions alternate to graphene areas exposed to the electric field of the Si substrate, which acts both as diode cathode and transistor gate, results in a two-terminal barristor with single-bias control of the Schottky barrier. The nanotip patterning favors light absorption, and the enhancement of the electric field at the tip apex improves photo-charge separation and enables internal gain by impact ionization. These features render the device a photodetector with responsivity ( 3 A W − 1 for white LED light at 3 mW cm − 2 intensity) almost an order of magnitude higher than commercial photodiodes. We extensively characterize the voltage and the temperature dependence of the device parameters, and prove that the multi-junction approach does not add extra-inhomogeneity to the Schottky barrier height distribution. We also introduce a new phenomenological graphene/semiconductor diode equation, which well describes the experimental I–V characteristics both in forward and reverse bias.

We study the effect of temperature and light on the I-V and C-V characteristics of a graphene/silicon Schottky diode. The device exhibits a reverse-bias photocurrent exceeding the forward current and achieves a photoresponsivity as high as $2.5\mathrm{A}/\mathrm{W}$ . We show that the enhanced photocurrent is due to photo-generated carriers injected in the graphene/Si junction from the parasitic graphene/SiO₂/Si capacitor connected in parallel to the diode. The same mechanism can occur with thermally generated carriers, which contribute to the high leakage current often observed in graphene/Si junctions.

We study the effect of polymer coating, pressure, temperature, and light on the electrical characteristics of monolayer ${\mathrm{WSe}}_2$ back-gated transistors with $\mathrm{Ni}/\mathrm{Au}$ contacts. Our investigation shows that the removal of a layer of poly(methyl methacrylate) (PMMA) or a decrease of the pressure change the device conductivity from p- to n-type. From the temperature behavior of the transistor transfer characteristics, a gate-tunable Schottky barrier at the contacts is demonstrated and a barrier height of $~$ 70 meV in the flat-band condition is measured. We also report and discuss a temperature-driven change in the mobility and the subthreshold swing that is used to estimate the trap density at the ${\mathrm{WSe}}_2{/\mathrm{SiO}}_2$ interface. Finally, from studying the spectral photoresponse of the ${\mathrm{WSe}}_2$ , it is proven that the device can be used as a photodetector with a responsivity of $~0.5{\mathrm{AW}}^{-1}$ at $700\mathrm{nm}$ and $0.37\mathrm{mW}/{\mathrm{cm}}^2$ optical power.

We studied the effects of low-energy electron beam irradiation up to 10 keV on graphene-based field effect transistors. We fabricated metallic bilayer electrodes to contact mono- and bi-layer graphene flakes on SiO₂, obtaining specific contact resistivity ${\rho }_c\approx 19\mathrm{k}\mathsf{\Omega }·{\mathsf{\mu }\mathrm{m}}^2$ and carrier mobility as high as 4000 cm²·V⁻¹·s⁻¹. By using a highly doped p-Si/SiO₂ substrate as the back gate, we analyzed the transport properties of the device and the dependence on the pressure and on the electron bombardment. We demonstrate herein that low energy irradiation is detrimental to the transistor current capability, resulting in an increase in contact resistance and a reduction in carrier mobility, even at electron doses as low as 30 e⁻/nm². We also show that irradiated devices recover their pristine state after few repeated electrical measurements.