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Ohmic Contact Fabrication Using a Focused-ion Beam Technique and Electrical Characterization for Layer Semiconductor Nanostructures
Published on: December 5, 2015
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Ohmic Contact Fabrication Using a Focused-ion Beam Technique and Electrical Characterization for Layer Semiconductor
Ruei-San Chen1, Chih-Che Tang2, Wei-Chu Shen2
1Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology; rsc@mail.ntust.edu.tw.
Journal of Visualized Experiments : Jove
|December 29, 2015
Summary
Electrical conductivity in molybdenum diselenide (MoSe2) layer semiconductors significantly increases as thickness decreases. This thickness-dependent conductivity, observed from micrometers down to nanometers, suggests surface-dominant transport properties for advanced electronic devices.
Area of Science:
- Materials Science
- Condensed Matter Physics
- Nanotechnology
Background:
- Two-dimensional (2D) layered semiconductors offer unique electronic and photonic properties due to quantum confinement.
- While enhanced properties are known in atomically thin 2D crystals, thickness effects at larger scales are less explored.
- Molybdenum diselenide (MoSe2) is a promising layered semiconductor for next-generation electronic and photonic devices.
Purpose of the Study:
- To investigate the electrical conductivity of molybdenum diselenide (MoSe2) layer crystals across a wide range of thicknesses.
- To explore the influence of thickness on the semiconducting behavior and transport properties of MoSe2.
- To assess the potential for MoSe2 and similar layered materials in advanced electronic applications.
Main Methods:
- Fabrication of MoSe2 layer crystals with thicknesses ranging from 6 nm to 2,700 nm using mechanical exfoliation.
- Formation of Ohmic contacts using focused-ion beam (FIB) deposition with platinum (Pt).
- Electrical characterization via current-voltage (I-V) measurements and temperature-dependent conductivity analysis.
- Material and interface analysis using high-resolution transmission electron microscopy (HRTEM), selected-area electron diffractometry (SAED), and energy-dispersive X-ray spectroscopy (EDX).
Main Results:
- A substantial thickness-dependent electrical conductivity was observed in MoSe2, increasing by over two orders of magnitude as thickness decreased from 2,700 nm to 6 nm.
- Conductivity values ranged from 4.6 to 1,500 Ω⁻¹cm⁻¹ across the studied thickness range.
- Thin MoSe2 multilayers exhibited weak semiconducting behavior with significantly lower activation energies (3.5–8.5 meV) compared to bulk MoSe2 (36–38 meV).
Conclusions:
- The findings demonstrate a strong correlation between thickness and electrical conductivity in MoSe2 layered semiconductors.
- Surface-dominant transport properties and high surface electron concentration are proposed as explanations for the observed phenomena in thin MoSe2.
- The results suggest that similar thickness-dependent effects may be present in other layered semiconductor materials like MoS2 and WS2.
