Tight-Binding Terahertz Plasmons in Chemical-Vapor-Deposited Graphene

Abstract

Transistor structures comprising graphene and sub-wavelength metal gratings hold a great promise for plasmon-enhanced terahertz detection. Despite considerable theoretical effort, little experimental evidence for terahertz plasmons in such structures was found so far. Here, we report an experimental study of plasmons in graphene-insulator-grating structures using Fourier transform spectroscopy in 5-10 THz range. The plasmon resonance is clearly visible above the Drude absorption background even in chemical vapor deposited (CVD) graphene with low carrier mobility ∼ 10 3 cm 2 /(V s). We argue that plasmon lifetime is weakly sensistive to scattering by grain boundaries and macoscopic defects which limits the mobility of CVD samples. Upon placing the grating in close proximity to graphene, the plasmon field becomes tightly bound below the metal stripes, while the resonant frequency is determined by the stripe width but not by grating period. Our results open the prospects of large-area commercially available graphene for resonant terahertz detectors.Graphene-based optoelectronic devices benefit from high-speed operation 1,2 , broadband response 3 , and compatibility with on-chip optical interconnects 4 . Their major drawback is low electromagnetic wave absorbance by a single sheet of graphene. This problem is readily resolved via coupling of incident light to plasmons bound either to adjacent metal nanoparticles 5,6 or to graphene itself 7 . Unlike plasmons in metals, intrinsic graphene plasmons offer ultra-strong field confinement 8 and tuning of resonant frequency with gate voltage 9,10 .Resonant excitation of plasmons in graphene-based photodetectors becomes increasingly difficult when going from infrared to terahertz (THz) range 11 as the plasmon quality factor scales linearly with frequency. Despite considerable effort 12-14 evidence of plasmon-assisted THz detection in graphene are scarce and were reported only for high-quality encapsulated graphene 15 or epitaxial graphene on SiC 16 . Experimental demonstrations of terahertz plasmons in absorbance spectra of graphene, including scalable chemical vapor deposited (CVD) samples, are more numerous [17][18][19] . At the same time, most such experiments dealt with ribbon-patterned where collection of photocurrent is hindered and boundary scattering is enhanced.In this paper, we study the plasmonic properties of a basic building block of graphene-based terahertz detector 13,20 , the CVD graphene-channel field-effect transistor with a grating gate. We find that plasmonic contribution to absorption spectra is pronounced at 5 − 10 THz frequencies despite moderate carrier mobility ∼ 10 3 cm 2 /V s and short momentum relaxation time τ p ∼ 50 fs. We further argue that plasmon lifetime in CVD-graphene (as it enters the quality factor) exceeds the relaxation time as extracted from mobility, in contrast to reports for encapsulated graphene. We find that metal grating placed in immediate vicinity to graphene modifies the resonant plasmon frequencies. In particular, the recipro...

Room-Temperature Amplification of Terahertz Radiation by Grating-Gate Graphene Structures

“…THz plasmon resonances in graphene are already observed in microribbons [50,60,61], rings, disks [52,53,62,63], and grating-gate structures [38]. However, it is worth mentioning that (i) here, we report the first experimental observations of such plasma standing waves with 100% gate tunable frequency and (ii) the plasmon-related extinction coefficient is going up 19%.…”

“…(For a discussion of crossover from the hydrodynamic to the ballistic regime and of the Cherenkov instability in graphene, see Refs. [38,39].) The suggested mechanism should work for any electronic spectrum, but calculations are more compact and physically transparent for parabolic spectrum characterized by the effective mass m. We thus restrict ourselves to the discussion of this case only.…”

“…Recently, some theoretical and experimental studies of grating-gate graphene structures utilizing plasma resonances have been reported [38][39][40]. In particular, the electromagnetic simulations of the graphene gratinggate structures [41] show the possibility of the resonant plasmons strongly coupled to THz radiation even at roomtemperature.…”

Grating Metamaterials Based on CdTe/CdMgTe Quantum Wells as Terahertz Detectors for High Magnetic Field Applications

“…On the other hand, we would like to stress that applicability of Equation (A4) must be limited since recent analitical considerations [41,42] show that this is rather the width of the metallic stripe, not the period of the grating, which determines the dispersion relation in a partially gated 2DEG.…”

Плазмонно-Резонансное Поглощение ТГц Излучения В Графене / Титова Е.И., Былинкин А.Н., Кащенко М.А., Михеев В.В., Жукова Е.С., Свинцов Д.А.

“…, а не периодом решетки. Мы сформулировали простую теорию для резонансных частот в нашем эксперименте, которая описывает экспериментальные данные без какихлибо подгоночных параметров[4].…”