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High Performance Molybdenum Disulfide Amorphous Silicon Heterojunction Photodetector

One important use of layered semiconductors such as molybdenum disulfide (MoS2) could be in making novel heterojunction devices leading to functionalities unachievable using conventional semiconductors. Here we demonstrate an ultrafast metal-semiconductor-metal heterojunction photodetector, made of MoS2 and amorphous silicon (a-Si), with rise and fall times of about 0.3 ms. This is more than an order of magnitude improvement over response times of conventional a-Si (~5 ms) and best reported MoS2 devices (~50 ms). The van-der-waals heterojunction presented here yields a high photoresponsivity of 210 mA/W at green light-the wavelength used in commercial imaging systems. This responsivity is 4X larger than that of the best MoS2 devices, and 2X larger than that of commercial a-Si devices. The 10X improvement in speed with high photoresponsivity provides a potential solution to a decades-long problem for thin film imagers and could find applications in large area electronics such as biomedical imaging and x-ray fluoroscopy.