Abstract
Terahertz (THz) waves have revealed a great potential for use in various fields and for a wide range of challenging applications. High-performance detectors are, however, vital for exploitation of THz technology. Graphene plasmonic THz detectors have proven to be promising optoelectronic devices, but improving their performance is still necessary. In this work, an asymmetric-dual-grating-gate graphene-terahertz-field-effect-transistor with a graphite back-gate was fabricated and characterized under illumination of 0.3THz radiation in the temperature range from 4.5K up to the room temperature. The device was fabricated as a sub-THz detector using a heterostructure of h-BN/Graphene/h-BN/Graphite to make a transistor with a double asymmetric-grating-top-gate and a continuous graphite back-gate. By biasing the metallic top-gates and the graphite back-gate, abrupt n+n (or p+p) or np (or pn) junctions with different potential barriers are formed along the graphene layer leading to enhancement of the THz rectified signal by about an order of magnitude. The plasmonic rectification for graphene containing np junctions is interpreted as due to the plasmonic electron-hole ratchet mechanism, whereas, for graphene with n+n junctions, rectification is attributed to the differential plasmonic drag effect. This work shows a new way of responsivity enhancement and paves the way towards new record performances of graphene THz nano-photodetectors.
Highlights
Over the last decades, development of terahertz (THz) devices in the so-called “THz-GAP” (0.1–10 THz) has been one of the hottest topics in modern physics due to a potential use of the THz radiation in various application areas such as security [1], material sensing [2], wireless communication [3] and others [4, 5]
The 2-terminal channel resistance of the ADGG-GTeraFET between drain and source was measured by using a standard lock-in technique where a pseudo-dc current (11 Hz) of 10 nA was injected into the drain and collected in the Source while the voltage drop between the drain and source contacts was measured by a lock-in amplifier (SR860)
To perform the THz photoresponse measurements, a THz solid-state harmonic generator source fabricated by RPG Radiometer Physics GmbH, with a customized design based on a dielectric resonator oscillator (DRO) with an initial frequency of 12.5 GHz and Schottky diode multiplier stages, was used to generate a continuous wave radiation source operating at 0.3 THz with an output power of about 6 mW
Summary
Development of terahertz (THz) devices in the so-called “THz-GAP” (0.1–10 THz) has been one of the hottest topics in modern physics due to a potential use of the THz radiation in various application areas such as security [1], material sensing [2], wireless communication [3] and others [4, 5]. Graphene exhibits high carrier mobility, fast carrier dynamics resulting in a high optical response speed It demonstrates a strong light–matter interaction that is related to the excitation of plasmons (i.e., collective oscillations of charge carries) whereby studies of THz rectification by graphene structures have led. It has been theoretically predicted that plasmonic THz rectification in a spatially inhomogeneous graphene channel could be significantly enhanced close to the Dirac point of graphene [23]. This theoretical prediction has not been experimentally verified so far. In this work we show that using the continuous back gate and asymmetric top double-grating gate one can create multiple junctions and enhance the detector responsivity by about an order of magnitude
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