Speaker
Description
Controlling the Fermi level is essential for tailoring the electronic properties of semiconductors. Here, we investigate two routes of chemical doping and defect control using scanning tunneling microscopy and spectroscopy. For V-doped MoSe$_2$, we study how substitutional V atoms influence its electronic structure. Although STM primarily probes the top Se layer and the dopants are not directly imaged, the topography exhibits defect-like features whose contrast reverses with the bias polarity: dark at positive sample bias and bright at negative bias. This is characteristic of negatively charged acceptor states, consistent with V substituting Mo. STS spectra show a Fermi-level shift toward the valence band, indicating that V doping drives MoSe$_2$ from intrinsic n-type toward p-type. For HfSe$_2$, we study defect control via thermal annealing. STS measurements under different annealing conditions show Fermi-level shifts toward the conduction band, suggesting that prolonged annealing enhances Se-vacancy formation, which acts as an electron donor. These results highlight how STM/STS links local defects with electronic properties, offering microscopic insight into Fermi-level tuning through doping and defect engineering.
