Towards high frequency heterojunction transistors: Electrical characterization of N-doped amorphous silicon-graphene diodes

Abstract

N-type doped amorphous hydrogenated silicon (a-Si:H) is deposited on top of graphene (Gr) by means of very high frequency (VHF) and radio frequency plasma-enhanced chemical vapor deposition (PECVD). In order to preserve the structural integrity of the monolayer graphene, a plasma excitation frequency of 140 MHz was successfully applied during the a-Si:H VHF-deposition. Raman spectroscopy results indicate the absence of a defect peak in the graphene spectrum after the VHF-PECVD of (n)-a-Si:H. The diode junction between (n)-a-Si:H and graphene was characterized using temperature dependent current-voltage (IV) and capacitance-voltage measurements, respectively. We demonstrate that the current at the (n)-a-Si:H-graphene interface is dominated by thermionic emission and recombination in the space charge region. The Schottky barrier height (qΦB), derived by temperature dependent IV-characteristics, is about 0.49 eV. The junction properties strongly depend on the applied deposition method of (n)-a-Si:H with a clear advantage of the VHF(140 MHz)-technology. We have demonstrated that (n)-a-Si:H-graphene junctions are a promising technology approach for high frequency heterojunction transistors.

Current Modulation of a Heterojunction Structure by an Ultra-Thin Graphene Base Electrode

“…More than 30 BC and BE interfacial diodes were analyzed in forward and reverse bias. A high dependence of the reverse current on the applied voltage was observed, thus obtaining rectifying ratios reaching up to 2 for BC and 17 for BE interfaces at 0.5 V. While a previous analysis of the (n)-a-Si:H/graphene junction had yielded rectifying ratios up to 5 orders of magnitude [ 13 ], it is known that experimental values of the parameters and the quality of semiconductor interfaces are strongly affected by the fabrication process.…”

“…A non-ideal diode behavior with a dominating thermionic transport mechanism is expected for the (n)-a-Si:H/graphene diodes [ 13 ]. Hence, the forward IV characteristics are given by the Schottky model where is the current density, the diode area, is the saturation current, the ideality factor, the Boltzmann constant and are the series resistances.…”

“…However, it must be noted that differently from the gated Ti/MoSe 2 of ref. [ 37 ], where the width of the space charge region is limited by the 2D crystal and controlled by the gate, the space charge region of the a-Si:H/graphene interface is much wider (~44 nm, as measured by capacitance-voltage characterization by Strobel et al [ 13 ]). Therefore, direct or FN tunneling mechanisms seem unlikely.…”

“…This was attributed to a reduction of the ion energies in the plasma due to the increased excitation frequency [ 12 ]. The damage-free deposition of a-Si:H by Very High Frequency PECVD (VHF-PECVD) on graphene allowed the electrical characterization of the (n)-a-Si:H/graphene junction by Strobel et al [ 13 ], which reported a Schottky barrier of 0.35–0.49 eV (depending on the substrate) and promising large rectification ratios of up to 10 5 . Here we present the electrical characterization of a graphene layer embedded between two (n)-a-Si:H layers deposited by VHF-PECVD and the ability of graphene to modulate the vertical current in the structure up to 40%.…”

Thermoelectric properties of doped graphene nanoribbons: density functional theory calculations and electrical transport

“…Recently, due to their unique properties, graphene and other 2D graphene-driven nanosheets have been studied both experimentally and theoretically by means of density functional theory (DFT). 2–9 The thermoelectric, mechanical, and optical properties of graphene and other graphene-like 2D nanosheets can be promoted by different processes, including doping with other elements as an impurity, 10 making ribbons 11 and heterostructures, 12 creating atomic vacancies, 13 and so on. One-dimensional structure of graphene namely graphene nanoribbons (GNRs) are thin ribbons of graphene that have brought additional benefits over graphene monolayer.…”