Exploiting Mg-Interdiffusion-Driven Work-Function Reduction in Ti/Mg/Ti Multilayers to Achieve Low-Resistivity Ohmic...

Area of Science:

• Materials Science and Engineering
• Semiconductor Device Physics

Background:

• Low-resistivity Ohmic contacts are critical for efficient beta-gallium oxide (β-Ga₂O₃) power electronics and deep-ultraviolet (DUV) optoelectronics.
• Existing contact methods face challenges in achieving the necessary low resistance and stability for β-Ga₂O₃.

Purpose of the Study:

• To develop and characterize a Ti/Mg/Ti multilayer metal stack for low-resistivity Ohmic contacts on (001) β-Ga₂O₃.
• To investigate the role of Mg interlayer and annealing atmosphere on contact properties and transport mechanisms.

Main Methods:

• Fabrication of Ti/Mg/Ti (20 nm/50 nm/20 nm) multilayer stacks on (001) β-Ga₂O₃.
• Utilized Ultraviolet Photoelectron Spectroscopy (UPS) and X-ray Photoelectron Spectroscopy (XPS) for work function and interfacial analysis.
• Employed Transmission Line Model (TLM) measurements at various temperatures and annealing conditions, alongside Transmission Electron Microscopy (TEM) for structural and compositional analysis.

Main Results:

• Achieved a contact resistivity of 6.25 × 10^-4 Ω·cm² for Ti/Mg/Ti annealed at 400 °C in Ar.
• Demonstrated tunneling-dominated carrier transport in inert atmospheres (Ar, vacuum, N₂) and thermionic emission in air, linked to oxidation levels.
• Incorporated contacts into β-Ga₂O₃ Metal-Semiconductor-Metal (MSM) photodetectors, achieving high responsivity (14,240.7 A/W) under DUV illumination.

Conclusions:

• The Ti/Mg/Ti multilayer stack effectively engineers low work function and provides oxidation protection for stable Ohmic contacts.
• Annealing atmosphere critically influences the contact transport mechanism, with Ar yielding superior tunneling-based transport.
• This approach offers a promising pathway for advanced β-Ga₂O₃ high-power and DUV optoelectronic devices.