Probing Interface Defects in Top-Gated MoS₂ Transistors with Impedance Spectroscopy

Area of Science:

• Materials Science
• Electrical Engineering
• Semiconductor Physics

Background:

• The HfO2/MoS2 interface is critical for next-generation transistors, but understanding its electronic properties and defects is essential for device performance.
• Characterizing interface traps in transition metal dichalcogenide (TMD) based Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) is challenging.

Purpose of the Study:

• To investigate the electronic properties and defect characteristics of the HfO2/MoS2 interface in top-gated MoS2 MOSFETs.
• To evaluate the effectiveness of multifrequency capacitance-voltage (C-V) and current-voltage (I-V) characterization, specifically impedance spectroscopy, as a metrology tool for interface defects.

Main Methods:

• Fabrication of few-layer MoS2 MOSFETs with HfO2 gate dielectric layers (8 and 13 nm) using atomic layer deposition and in-situ UV-O3 surface functionalization.
• Multifrequency capacitance-voltage (C-V) and current-voltage (I-V) measurements to analyze the impedance response of the HfO2/MoS2 gate stack.
• Extraction of interface trap density (Dit) using high-low frequency and multiple-frequency C-V methods.

Main Results:

• Impedance spectroscopy revealed frequency-dependent distortions and dispersions, indicative of specific interface defects at the HfO2/MoS2 interface.
• Extracted interface trap density (Dit) values ranged from 2 × 10^11 to 1.2 × 10^13 cm^-2 eV^-1, depending on MoS2 layer thickness and HfO2 thickness.
• Continuous HfO2 films were confirmed by low gate leakage currents (<10^-7 A/cm^2), attributed to the combined UV-O3 and HfO2 deposition process.

Conclusions:

• Multifrequency impedance spectroscopy is a viable approach for characterizing electrically active defects at the HfO2/MoS2 interface using simple transistor structures.
• This metrology tool is applicable to various TMD materials, surface treatments, and gate oxides, aiding the development of advanced TMD-based MOSFETs.