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Graphene photodetectors are highly attractive owing to its ultra-fast and wide-range spectral response from visible to infrared benefit from the superior carrier mobility and the linear dispersion with zero bandgap of graphene. The application of graphene photodetectors however is seriously limited by the low intrinsic responsivity in the order of ∼10 mA/W. Here, we demonstrate photogating field-effect transistors based on pure monolayer graphene with simple device structures. The light absorption in the heavily n-doped silicon/silicon oxide (Si/SiO2) substrate generates an additional photovoltage that effectively modulates the conductance of graphene, leading to room temperature graphene photodetectors with high responsivity of ∼500 A/W for 450 nm light and ∼4 A/W for 1064 nm light, respectively. The generated photocurrent changes with applied gate voltage and shows a strongly nonlinear power dependence. Meanwhile, the photoresponse of graphene exhibits a cut-off wavelength of ∼1100 nm, confirming the dominance photogating effect caused by light absorption in Si/SiO2 substrate. Considering the great compatibility of graphene to Si technology, our result paves a way for high-performance chip-integrated photodetectors. [ABSTRACT FROM AUTHOR]

2H phase Molybdenum ditelluride (MoTe2) is a layered two-dimensional (2D) semiconductor that has recently gained extensive attention for its intriguing properties, demonstrating great potential for nanoelectronics and optoelectronics. Optimizing the electric contacts to MoTe2 is a critical step for realizing high performance devices. Here, we demonstrate Co/hBN tunnel contacts to few-layer MoTe2. In sharp contrast to the p-type conduction of Co contacted MoTe2, Co/hBN tunnel contacted MoTe2 devices show clear n-type transport properties. Our first principles calculation reveals that the inserted few-layer hBN strongly interacts with Co and significantly reduces its work-function by ∼1.2 eV, while MoTe2 itself has a much weaker influence on the work-function of Co. This allows us to build MoTe2 diodes using the mixed Co/hBN and Co contact architecture, which can be switched from p-n type to n-p type by changing the gate-voltage, paving the way for engineering multi-functional devices based on atomically thin 2D semiconductors. [ABSTRACT FROM AUTHOR]