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Megan Beck1 Vinod Sangwan1 Alex Henning1 Jiajia Luo1 Hadallia Bergeron1 Junmo Kang1 Itamar Balla1 Hadass Inbar1 Lincoln Lauhon1 Mark Hersam1

1, Northwestern University, Evanston, Illinois, United States

The ubiquity of a self-aligned gate in integrated circuits is due to processing simplicity, versatility, and compatibility with diverse technologies, allowing for significantly increased circuit complexity. Meanwhile, two-dimensional (2D) materials have recently shown tremendous potential for digital and analog electronics due to high mobility, superior scaling limits, and arbitrary permutations of materials in defect-free van der Waals heterojunctions (vdWHs). Therefore, the combination of 2D materials with self-aligned fabrication approaches has the potential to unite these characteristics in a platform with significant advantages for next-generation electronics. Toward this end, a general self-aligned fabrication scheme is reported here whereby control of lithography resist undercut profiles enables the realization of a diverse class of short-channel electronic devices based on van der Waals materials [1]. Self-alignment enables the fabrication of 135 nm channel source-gated transistors in monolayer MoS2 with reduced short-channel effects and near-ideal current saturation characteristics. Additionally, self-alignment of van der Waals p-n heterojunction diodes based on black phosphorus and MoS2 achieves complete electrostatic control of both the p-type and n-type constituent semiconductors in a dual-gated geometry, resulting in gate-tunable mean and variance of anti-ambipolar Gaussian transfer characteristics. Through finite-element device simulations, the operating principles of source-gated transistors and dual-gated anti-ambipolar devices are elucidated, thus providing design rules for additional devices that employ self-aligned geometries. In addition, this technique reduces the number of lithography steps for fabricating complicated geometries, is scalable to large areas via photolithography with sub-wavelength channel lengths, and can be generalized to mixed-dimensional organic and inorganic nanomaterials while minimizing electrical shorts through porosity, pinholes, or related defects. Overall, this self-aligned fabrication method represents an important step toward the scalable integration of van der Waals heterojunction devices into more sophisticated circuits and systems.

[1] V. K. Sangwan, M. E. Beck, A. Henning, J. Luo, H. Bergeron, J. Kang, I. Balla, H. Inbar, L. J. Lauhon, and M. C. Hersam, “Self-aligned van der Waals heterojunction diodes and transistors,” Nano Letters, 18, 1421-1427 (2018).

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