Impact of Transport Anisotropy on the Performance of van der Waals Materials-Based Electron Devices

Layered van der Waals (vdW) semiconductors have emerged as preferred materials for building next-generation electronic devices, such as diodes and field-effect transistors (FETs), because of their capability of providing high mobility at the nanometer-scale thickness, as well as their flexibility and pristine interfaces. However, the inherent "vdW gaps" in these materials lead to much larger cross-plane resistivity, with respect to in-plane resistivity, thereby forming intriguing transport anisotropy. In this article, using extensive numerical simulations, it is found that this anisotropy introduces anomalous current transport behavior in vdW-based electron devices in which the current conducts in both the in-plane and cross-plane directions, including stacked heterojunction diodes and thin-film transistors (TFTs). Our study reveals for the first time that transport anisotropy degrades the performance of these devices, especially when devices are scaled (<0.6 mu m) and/or relatively thicker materials (>4 nm) are used. Potential solutions to alleviate degradation are discussed as well.