Contact-geometry-dependent vertical channel migration in multilayer ReS2 field-effect transistors

Abstract

Understanding the interlayer charge transport in multilayer two-dimensional (2D) semiconductors is crucial for optimizing device performance and interface engineering in emerging nanoelectronic systems. In particular, the presence of significant interlayer resistance such as multilayers of ReS₂ induces bias-dependent redistribution of conduction channels, resulting in channel migration vertically. Here, we experimentally investigate the contact-geometry-dependent channel migration behavior in multilayer ReS₂ field-effect transistors (FETs) using a vertically stacked h-BN/ReS₂/h-BN heterostructure. Devices with symmetric top contacts, symmetric edge contacts, and asymmetric (hetero) contact configurations are fabricated on the same flake. Systematic measurements of transconductance (g_m), its derivative (dg_m), and threshold voltage (V_th), combined with theoretical modeling based on Thomas–Fermi screening and interlayer resistor networks, reveal that top-contacted devices exhibit a downward migration of the main conduction channel with increasing drain bias. In contrast, edge-contacted devices maintain a stable bottom-centered conduction profile, independent of drain bias conditions. In the hetero-contact configuration, where the source electrode is edge-contacted, direct carrier injection into all layers enhances vertical channel selectivity, resulting in earlier onset and more pronounced channel migration even at relatively low drain bias. In addition, the field-effect mobility extracted from gₘ and its agreement with low-field mobility from the Y-function method confirms that interfacial scattering, rather than contact resistance, predominantly limits device performance. This study provides direct experimental insights into vertical charge migration in multilayer 2D materials and offers design guidelines for engineering contact strategies in future 2D FETs.