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

Abstract

At high phonon temperature, defect-mediated electron-phonon collisions (supercollisions) in graphene allow for larger energy transfer and faster cooling of hot electrons than the normal, momentum-conserving electron-phonon collisions. Disorder also affects the heat flow between electrons and phonons at very low phonon temperature, where the phonon wavelength exceeds the mean free path. In both cases, the cooling rate is predicted to exhibit a characteristic cubic power law dependence on the electron temperature, markedly different from the T 4 dependence predicted for pristine graphene. The impact of defect-induced cooling on the performance of optoelectronic devices is still largely unexplored. Here we study the cooling mechanism of hotelectron bolometers based on epitaxial graphene quantum dots where the defect density can be controlled with the fabrication process. The devices with high defect density exhibit the cubic power law. Defect-induced cooling yields a slower increase of the thermal conductance with increasing temperature, thereby greatly enhancing the device responsivity compared to devices with lower defect density and operating with normal-collision cooling.

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.…”

“…The mask is removed in the last step of the process by aqua regia, leaving the graphene fully exposed. Our previous work showed that the fabrication process modifies the graphene doping and quality [31]. The aqua regia is a strong hole dopant and affects the charge carrier density, while the metal sputtering induces defects in the graphene.…”

“…The aqua regia is a strong hole dopant and affects the charge carrier density, while the metal sputtering induces defects in the graphene. These defects affect the electron cooling mechanism, yielding the counterintuitive result of enhancing the device performance [31]. At the end of the process, the graphene has a bowtie shape, with the quantum dot in the middle connected to triangular source and drain electrodes, as shown in figure 1.…”

“…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].…”

Bolometer operating at the threshold for circuit quantum electrodynamics

“…Although we can only measure the total thermal conductance, we note that it scales roughly linearly with the bath temperature. This indicates that the photonic thermal conductance [101] is dominating, since the phononic contribution scales as the bath temperature to the power ranging from 2 to 4 [102][103][104][105][106]. Electron diffusion also seems unlike due to the utilized superconducting leads that suppress this effect [99].…”