Limits on the bolometric response of graphene due to flicker noise

Abstract

We study the photoresponse of graphene field effect transistors using scanning photocurrent microscopy in near and far field configurations, and we find that the response of graphene under a source-drain bias voltage away from the contacts is dominated by the bolometric effect caused by laser induced heating. We find no significant change in the photocurrent with the optical modulation frequency upto 100 kHz. Although the magnitude of the bolometric current scales with bias voltage, it also results in noise. The frequency dependence of this noise indicates that it has a 1/f character, scales with the bias voltage and limits the detectable bolometric photoresponse at low optical powers.Graphene 1 -an isolated single layer of graphitepromises to be useful for photodetection and other light harvesting devices because of its gapless band structure and large broadband absorption. Photodetectors made using graphene 2 involving global illumination have been reported and the quantities of interest are the responsivity and response time. In these measurements, the role of different mechanisms involved in photogeneration is complex. In a recent study, 3 the infrared photoresponse has been observed to change with the graphene channel length suggesting different physical mechanisms playing a role at the electrodes and far away from them.Scanning photocurrent microscopy (SPCM) measurements are useful in elucidating the mechanism of photocurrent generation in graphene since the spatially resolved mapping of current can yield information about the photoresponse at different regions on the graphene device such as contacts and p-n junctions. Several mechanisms 4 have been identified such as the photovoltaic, 5-8 photothermoelectric 9,10 and bolometric effects. 11In this paper, we discuss SPCM measurements on graphene field effect transistor (FET) devices using both near and far field configurations and focus on homogeneous graphene away from the electrodes. The photocurrent generation in graphene is dominated by the bolometric effect far away from the electrodes and by the photovoltaic effect due to the built-in electric field at the contacts. The bolometric effect refers to the resistance change induced in the device by laser-induced heating and it has previously been seen in carbon nanotubes, 12 graphene 11 and in 100 nm thick black phosphorus. 13 Our main finding is that the bolometric effect, which is only visible at non-zero bias voltages is accompanied by flicker noise which scales with bias and limits the detectable bolometric signal.Graphene devices were fabricated by exfoliation of graphite on degenerately doped silicon substrates with 300 nm of silicon dioxide. Monolayer graphene flakes were identified by visual contrast in optical microscope and with Raman spectroscopy. Electron beam lithograa) Electronic mail: deshmukh@tifr.res. in FIG. 1. Schematic of the (a) near-field and (b) far-field measurement setup. In (a), a tapered fiber is used for illumination (635 nm laser diode) as part of a home-built NSOM, and in (b...

Near-field photocurrent nanoscopy on bare and encapsulated graphene

“…1a . The setup is based on a scattering-type scanning near-field optical microscope (s-SNOM) 26 42 augmented with electrical contact to the sample to measure currents in situ 28 29 30 31 32 33 34 35 36 37 38 . In contrast to conventional s-SNOM, we do not need to measure the outscattered light but rather directly measure current induced by the near-field as explained in the following.…”

“…Here we demonstrate fully non-invasive room-temperature scanning near-field photocurrent nanoscopy 28 29 30 31 32 33 34 35 36 37 38 for the first time applied on graphene with infrared frequencies and use it to study the nanoscale optoelectronic properties of graphene devices that can later be used for real applications. This technique is based on electrical probing of the photoresponse due to strongly localized heating.…”

Unveiling the detection dynamics of semiconductor nanowire photodetectors by terahertz near-field nanoscopy

“…Very recently, scattering-type scanning near-field optical microscopy (s-SNOM) has been exploited at THz frequencies to map photocurrents in graphene 46 with subdiffraction spatial resolution, exploiting lightning-rod effects in a metal-coated atomic force microscopy (AFM) tip illuminated by the THz output of a bulky, table-top, gas laser. 47 Here, we conceive and devise a compact, portable, scanning near-field system that functions at THz frequencies and is capable of simultaneously performing photocurrent nanoscopy [48][49][50][51][52][53][54][55][56][57][58][59] and detectorless near-field imaging 60 of a 1D NW field-effect nanodetector with 35 nm spatial resolution, which corresponds to a wavelength fraction <λ/3000. The system comprises a continuous-wave (CW) THz quantum cascade laser (QCL) coupled to s-SNOM and is here innovatively exploited to trace and map, unambiguously, the physical mechanisms inducing light detection at THz frequencies.…”

1 / f noise in van der Waals materials and hybrids

“…While these van der Waals materials individually offer remarkable properties, they can further be combined to synthesize distinct new functionalities [13,17,[27][28][29][30][31][32][33][34][35], serving as promising building blocks of future electronic and optoelectronic devices. One key factor that determines the device performance, and dictates the detection limits and sensitivity, is the level of low-frequency 1/f noise present in the system [36][37][38][39][40][41][42][43][44]. Although the low-frequency noise is usually undesirable which, for example, introduces phase noise in high-speed operations [41], it can also offer insights into the disorder configuration [37,38] and kinetics in the system [45,46].…”