Giant nonlinearity in epitaxial graphene moiré superlattices for RF energy harvesting

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Abstract
The nonlinear Hall effect (NLHE) in two-dimensional moiré superlattice materials offers promising opportunities for radio frequency (RF) energy harvesting, but challenges persist in achieving both room-temperature controllable NLHE and scalable fabrication. Here, we report the manipulation of NLHE in the 4-inch epitaxial graphene-germanium (Gr-Ge) heterostructures for practical energy harvesting. The stacking of stripe-phase Ge(110) surface with monolayer graphene generates periodic hexagonal moiré superlattices exhibiting reduced C1v symmetry configuration. The intrinsic symmetry breaking at the Gr-Ge hetero-interface enables remarkable room-temperature NLHE strength of ~103 μmV-1, which exceeds all state-of-the-art moiré or bulk materials systems. Moreover, by adopting the series-connected nonlinear Hall rectifiers (NRs) array configuration and a dual-functional layout design with back-end-of-line (BEOL) processes, we develop self-contained rectenna dies incorporating a 4×4 NRs array with the remarkable rectified voltage exceeding 20 mV at -16 dBm input power, which is sufficient for driving commercial booster converter operation. Besides, we demonstrate the use of NRs array to realize ambient RF energy harvesting by powering an LED at room temperature. Our results demonstrate the successful transition of NLHE-based rectification from theoretical concept to practical applications. Beyond RF energy harvesting, the low-symmetry Gr-Ge moiré superlattices open new avenues for next-generation application in nonlinear electronics, photonics, and optoelectronic technologies.

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