Tuning the electronic structure of two-dimensional semiconductor junctions

Lateral junctions between two-dimensional (2D) semiconductors are conceptually the smallest possible electronic devices.

This project investigates the basic physics of these systems as the type of band alignment, the band bending and depletion region, which are decisive parameters for any application.

Semiconductor junctions composed of 2D transition metal dichalcogenides (TMDs) will be prepared on hexagonal boron nitride (hBN) or graphene (Gr) on Ir(111).

The use of the single-crystalline metal substrate allows the application of surface science methods for preparation and characterization, while the ultrathin buffer layer leaves the intrinsic properties of TMDs undisturbed.

Intercalation of guest atoms between the buffer layer and Ir will be used as an elegant and non-invasive method for doping the TMDs.

This will also tune intrinsic band bending at the 1D-interface of the TMD junctions, which is yet to be explored for various 2D systems.

To separate the effect of inhomogeneous doping and inhomogeneous structure, two types of lateral TMD junctions will be prepared: Homojunctions will be achieved by doping only one part of the TMD island by extending it over the interface of intercalated patches in hBN.

Heterojunctions will be composed of two different TMD materials grown on homogeneous vdW substrate, either fully intercalated or pristine. Samples will be prepared by combining two TMDs (ReS2 and WS2) and two dopants (n and p).

Scanning tunneling spectroscopy (STS) and Kelvin probe force microscopy (KPFM) will be used for the characterization of the 1D-interfaces and the reconstruction of the band diagrams.

Dielectric screening induced by the substrate will be analyzed by comparing values of the band gaps and shifts of critical energy points between different systems. This will deepen the understanding of the origin of band bending in 2D systems. Inelastic electron tunneling spectroscopy (IETS) will be used as a potentially new technique for detecting excitons.