Simultaneous\nCharacterization of In-Plane and Cross-Plane\nResistivities in Highly Anisotropic 2D Layered Heterostructures

Understanding\nand characterizing the intrinsic properties of charge\ncarrier transport across the interfaces in van der Waals heterostructures\nis critical to their applications in modern electronics, thermoelectrics,\nand optoelectronics. However, there are very few published cross-plane\nresistivity measurements of thin samples because these inherently\n2-probe measurements must be corrected for contact and lead resistances.\nHere, we present a method to extract contact resistances and metal\nlead resistances by fitting the width dependence of the contact end\nvoltages of top and bottom electrodes of different contact widths\nto a model based on current crowding. These contributions are then\nsubtracted from the total 2-probe cross-plane resistance to obtain\nthe cross-plane resistance of the material itself without needing\nmultiple devices and/or etching steps. This approach was used to measure\ncross-plane resistivities of a (PbSe)<sub>1</sub>(VSe<sub>2</sub>)<sub>1</sub> heterostructure containing alternating layers of PbSe and\nVSe<sub>2</sub> with random in-plane rotational disorder. Several\nsamples measured exhibited a 4 order of magnitude difference between\ncross-plane and in-plane resistivities over the 6–300 K temperature\nrange. We also reported the observation of charge density wave transition\nin the cross-plane transport of the (PbSe)<sub>1</sub>(VSe<sub>2</sub>)<sub>1</sub> heterostructure. The device fabrication process is\nfully liftoff compatible, and the method developed enables the straightforward\nmeasurement of the resistivity anisotropy of most thin film materials\nwith nm thicknesses.