Creating Optoelectronic Devices from Atomically Thin Materials Grown by Chemical Vapor Deposition
Two-dimensional materials such as graphene and transition metal dichalcogenides (TMDs) are ideal candidates to create ultra-thin optoelectronics that can be flexible and semitransparent. Although optoelectronic devices based on TMDs have demonstratedremarkable performance, most devices are created using techniques that are not suitable for mass production, such as mechanical exfoliation of monolayer flakes and patterning by electron-beam lithography. Here we show device fabrication processes that are suitable for mass production and based on the growth of high-quality atomically thin materials such as graphene, MoS2, WS2,MoSe2 and WSe2 by chemical vapor deposition. Using as-grown materials and photolithography, we achieved photodetectors with high sensitivity and record shot-noise limited detectivities of 8.7x10^14 Jones in ambient condition and even higher when sealed with a protective layer. We studied MoS2 based devices with gold electrodes and graphene electrodes. The devices with graphene electrodes have a tunable band alignment and are especially attractive for scalable ultra-thin flexible optoelectronics. However, these devices are hindered by a slow photoresponse caused by charge trapping. Gas adsorbates, such as H2O and O2, which create charge traps, are a main contribution to both the highresponsivity and the slow photoresponse. We studied the effect of ambient conditions on the performance of MoS2 photodetectors. We show that vacuum pumping with laser illumination combined with hydrophobic substrates removes most of the adsorbates, paving the way to TMD photodetectors with high responsivity and fast response.
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