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Fully encapsulated and stable black phosphorus field-effect transistors

Arora, H.; Fekri, Z.; Vekariya, Y. N.; Chava, P.; Watanabe, K.; Taniguchi, T.; Helm, M.; Erbe, A.


Black phosphorus (BP) has quickly gained popularity in the scientific community owing to its interesting semiconducting properties, such as direct bandgap, high mobility, and intrinsic ambipolar behavior. However, its sensitivity to oxygen, moisture, and other air species has restricted its integration into active devices. Here, we employ lithography-free via-encapsulation scheme to fabricate fully-encapsulated BP-based field-effect transistors (FETs). The full encapsulation is achieved by sandwiching the BP layers between top and bottom hexagonal boron nitride (hBN) layers; top hBN passivating the BP layer from the environment and bottom hBN acting as a spacer and suppressing charge transfer to the BP layer from the SiO2 substrate. The embedded via-metal-electrodes allow us to perform reliable electrical measurements of the BP FETs. Based on our results, we find that the electronic properties of the via-encapsulated BP FETs are significantly improved compared to unencapsulated devices and a clear metal–insulator transition is observed which remained missing in the latter. We further establish that the via-contacting scheme leads to superior results compared to graphene-hBN heterostructures and bare hBN layers combined with evaporated metal contacts (both use top and bottom hBN to encapsulate BP) by revealing a higher mobility, lower hysteresis, and long-term ambient-stability in BP FETs.

Keywords: two-dimensional semiconductors; black phosphorus; field-effect transistors; hexagonal boron nitride; encapsulation

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