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 . 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.
 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).