Ultra-broadband photodetectors based on epitaxial graphene quantum dots

Abstract

Graphene is an ideal material for hot-electron bolometers, due to its low heat capacity and weak electron-phonon coupling. Nanostructuring graphene with quantum dot constrictions yields detectors with extraordinarily high intrinsic responsivity, higher than 1×10 9 V W -1 at 3K. The sensing mechanism is bolometric in nature: the quantum confinement gap causes a strong dependence of the electrical resistance on the electron temperature. Here we show that this quantum confinement gap does not impose a limitation on the photon energy for light detection and these quantum dot bolometers work in a very broad spectral range, from terahertz, through telecom to ultraviolet radiation, with responsivity independent of wavelength. We also measure the power dependence of the response. Although the responsivity decreases with increasing power, it stays higher than 1×10 8 V W -1 in a wide range of absorbed power, from 1 pW to 0.4 nW.

Effect of defect-induced cooling on graphene hot-electron bolometers

“…We recently showed that quantum dots patterned from epitaxial graphene on SiC exhibit a very strong dependence of the electrical resistance on temperature, higher than 100 M K -1 , yielding extraordinary values of bolometric responsivity, larger than 10 9 V W -1 [15,16]. The strong temperature dependence of the resistance is caused by the quantum confinement gap of the dots and depends on the dot diameter.…”

Nanostructured graphene for nanoscale electron paramagnetic resonance spectroscopy

“…By using T 1 ∼1 μs (at 4.3 K) [32], we find P 1M ∼6×10 −17 W. If a monolayer of SMMs covers the whole graphene area, about 20 μm 2 for the smallest bowties, for an approximate SMM size of 1 nm, we estimate 2×10 7 SMMs covering the graphene and absorbing about 1.2 nW. This power is much higher (by at least two orders of magnitude) than the smallest absorbed power that we can measure with the graphene quantum dots [11,12,31], therefore power absorption from monolayer SMMs will cause a change in the power absorbed by the graphene quantum dots that should be easily measurable.…”

“…For most SMMs the blocking temperature is on the order of a few Kelvins. Magnetic bistability was first discovered in [Mn 12 [15]. This SMM has a core of twelve magnetically coupled manganese ions (Mn 12 ) [16] and its relaxation time that can be years below 2 K [15,17].…”

“…The strong temperature dependence of the resistance is due to thermal activation of the electrical current over an energy barrier that is inversely proportional to the dot diameter [11]. This simple device design yields detectors with electrical responsivity as high as 10 10 V W -1 and noise equivalent power below 2 × 10 −16 W Hz −0.5 at 2.5 K [11,12,31]. These figures of merit are based on the absorbed power and the absorbed power can be measured directly from the bolometer current-voltage characteristics [11,12].…”

“…Notably, one of the simplest designs, based on opening a quantum confinement gap by patterning graphene with a nanoconstriction (quantum dot), yields bolometers with extraordinarily high electrical responsivities, larger than 10 9 V W -1 at temperatures of a few Kelvins. These graphene quantum dot bolometers have ultrabroadband response, including regions of the electromagnetic spectrum that are notoriously difficult to work with, such as the Terahertz range [11,12], and are competitive with the most sensitive commercial bolometers [13]. One key feature of this simple photodetector design is that the graphene is fully exposed on the surface of the substrate, with no protective encapsulation, no absorber layer necessary to enhance light absorption, and no top gate needed for the device operation.…”