Bandgap, mid-gap states, and gating effects in MoS2

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology

Background:

• Layered materials like transition metal dichalcogenites (TMDs) are key for novel heterostructures.
• Molybdenum disulfide (MoS2), a stable and high-mobility semiconductor, shows promise for post-silicon electronics.
• Controlling the Fermi energy (EF) is critical for MoS2 applications in switching, photonics, and flexible electronics.

Purpose of the Study:

• To understand the dependence of Fermi energy (EF) on doping and gating in MoS2.
• To investigate the factors influencing N-doping in bulk and thin-film MoS2.
• To correlate scanning tunneling microscopy/spectroscopy (STM/STS) with field-effect transistor (FET) measurements.

Main Methods:

• Gated scanning tunneling microscopy (STM) and spectroscopy (STS) were performed on MoS2 samples.
• Transport measurements were conducted using a field-effect transistor (FET) device configuration.
• Bandgap and Fermi energy (EF) evolution with gate voltage were tracked.

Main Results:

• For bulk MoS2, a bandgap of ~1.3 eV and EF ~0.35 eV below the conduction band were measured, consistent with N-doping.
• Sulfur vacancies were identified as the cause of N-doping in bulk MoS2 samples.
• Thin MoS2 films on SiO2 exhibited significantly higher N-doping, attributed to sample-substrate interface charge traps.

Conclusions:

• The study elucidates the doping mechanisms in MoS2, differentiating between bulk and thin-film behavior.
• Understanding Fermi energy modulation is crucial for optimizing MoS2 for electronic applications.
• Interface effects significantly impact doping in thin MoS2 films, offering insights for device engineering.