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Register a new userTHz detection with epitaxial graphene field effect transistors on silicon carbide
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Miriam Serena Vitiello Prof
Publication date
2018
fields
Physics
and research's language is
English
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We report on room temperature THz detection by means of antenna-coupled field effect transistors fabricated by using epitaxial graphene grown on silicon carbide substrate. Two independent detection mechanisms are found: plasma wave assisted-detection and thermoelectric effect, which is ascribed to the presence of junctions along the FET channel. The superposition of the calculated functional dependence of both the plasmonic and thermoelectric photovoltages on the gate bias qualitatively well reproduces the measured photovoltages. Additionally, the sign reversal of the measured photovoltage demonstrates the stronger contribution of the plasmonic detection compared to the thermoelectric mechanism. Although responsivity improvement is necessary, these results demonstrate that plasmonic detectors fabricated by epitaxial graphene on silicon carbide are potential candidates for fast large area imaging of macroscopic samples.
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This article presents a review of epitaxial graphene on silicon carbide, from fabrication to properties, put in the context of other forms of graphene.
Palladium diselenide (PdSe2) is a recently isolated layered material that has attracted a lot of interest for the pentagonal structure, the air stability and the electrical properties largely tunable by the number of layers. In this work, PdSe2 is used in the form of multilayer as the channel of back-gate field-effect transistors, which are studied under repeated electron irradiations. Source-drain Pd leads enable contacts with resistance below 350 kOhm um. The transistors exhibit a prevailing n-type conduction in high vacuum, which reversibly turns into ambipolar electric transport at atmospheric pressure. Irradiation by 10 keV electrons suppresses the channel conductance and promptly transforms the device from n-type to p-type. An electron fluence as low as 160 e-/nm2 dramatically change the transistor behavior demonstrating a high sensitivity of PdSe2 to electron irradiation. The sensitivity is lost after few exposures, that is a saturation condition is reached for fluence higher than 4000 e-/nm2. The damage induced by high electron fluence is irreversible as the device persist in the radiation-modified state for several hours, if kept in vacuum and at room temperature. With the support of numerical simulation, we explain such a behavior by electron-induced Se atom vacancy formation and charge trapping in slow trap states at the Si/SiO_2 interface.
In this work, we present an investigation regarding how and why molecular hydrogen changes the electronic properties of graphene field effect transistors. We demonstrate that interaction with H2 leads to local doping of graphene near of the graphene-contact heterojunction. We also show that such interaction is strongly dependent on the characteristics of the metal-graphene interface. By changing the type metal in the contact, we observe that Ohmic contacts can be strongly or weakly electrostatically coupled with graphene. For strongly coupled contacts, the signature of the charge transfer effect promoted by the contacts results on an asymmetric ambipolar conduction, and such asymmetry can be tunable under interaction with H2. On the other hand, for contacts weakly coupled with graphene, the hydrogen interaction has a more profound effect. In such situation, the devices show a second charge neutrality point in graphene transistor transfer curves (a double-peak response) upon H2 exposure. We propose that this double-peak phenomenon arises from the decoupling of the work function of graphene and that of the metallic electrodes induced by the H2 molecules. We also show that the gas-induced modifications at the metal-graphene interface can be exploited to create a controlled graphene p-n junction, with considerable electron transfer to graphene layer and significant variation in the graphene resistance. These effects can pave the way for a suitable metallic contact engineering providing great potential for the application of such devices as gas sensors.
In this work we test graphene electrodes in nano-metric channel n-type Organic Field EffectTransistors (OFETs) based on thermally evaporated thin films of perylene-3,4,9,10-tetracarboxylic acid diimide derivative (PDIF-CN2). By a thorough comparison with short channel transistors made with reference gold electrodes, we found that the output characteristics of the graphene-based devices respond linearly to the applied biases, in contrast with the supra-linear trend of gold-based transistors. Moreover, short channel effects are considerably suppressed in graphene electrodes devices. More specifically, current on/off ratios independent of the channel length (L) and enhanced response for high longitudinal biases are demonstrated for L down to ~140 nm. These results are rationalized taking into account the morphological and electronic characteristics of graphene, showing that the use of graphene electrodes may help to overcome the problem of Space Charge Limited Current (SCLC) in short channel OFETs.
For the first time, n-type few-layer MoS2 field-effect transistors with graphene/Ti as the hetero-contacts have been fabricated, showing more than 160 mA/mm drain current at 1 {mu}m gate length with an on-off current ratio of 107. The enhanced electrical characteristic is confirmed in a nearly 2.1 times improvement in on-resistance and a 3.3 times improvement in contact resistance with hetero-contacts compared to the MoS2 FETs without graphene contact layer. Temperature dependent study on MoS2/graphene hetero-contacts has been also performed, still unveiling its Schottky contact nature. Transfer length method and a devised I-V method have been introduced to study the contact resistance and Schottky barrier height in MoS2/graphene /metal hetero-contacts structure.
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