1. ZDNet – Researchers working at the Institute of Photonic Sciences (ICFO) in Barcelona have built a super-sensitive photodetector by combining graphene with semiconducting quantum dots that outperforms other graphene based devices by a billion times.
Speaking to PhysicsWorld , lead researcher Gerasimos Konstantatos explains: “We managed to successfully combine graphene with semiconducting nanocrystals to create complete new functionalities in terms of light sensing and light conversion to electricity.”
Graphene is an attractive material for optoelectronics1 and photodetection applications because it offers a broad spectral bandwidth and fast response times. However, weak light absorption and the absence of a gain mechanism that can generate multiple charge carriers from one incident photon have limited the responsivity of graphene-based photodetectors to ~10−2 A W−1. Here, we demonstrate a gain of ~10^8 electrons per photon and a responsivity of ~10^7 A W−1 in a hybrid photodetector that consists of monolayer or bilayer graphene covered with a thin film of colloidal quantum dots. Strong and tunable light absorption in the quantum-dot layer creates electric charges that are transferred to the graphene, where they recirculate many times due to the high charge mobility of graphene and long trapped-charge lifetimes in the quantum-dot layer. The device, with a specific detectivity of 7 × 10^13 Jones, benefits from gate-tunable sensitivity and speed, spectral selectivity from the short-wavelength infrared to the visible, and compatibility with current circuit technologies.
Graphene is an attractive material for use in optical detectors because it absorbs light from mid-infrared to ultraviolet wavelengths with nearly equal strength. Graphene is particularly well suited for bolometers—devices that detect temperature-induced changes in electrical conductivity caused by the absorption of light—because its small electron heat capacity and weak electron–phonon coupling lead to large light-induced changes in electron temperature. Here, we demonstrate a hot-electron bolometer made of bilayer graphene that is dual-gated to create a tunable bandgap and electron-temperature-dependent conductivity. The bolometer exhibits a noise-equivalent power (33 fW Hz–1/2 at 5 K) that is several times lower, and intrinsic speed (over 1 GHz at 10 K) three to five orders of magnitude higher than commercial silicon bolometers and superconducting transition-edge sensors at similar temperatures
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