Highly reflective Ag-Cu alloy-based ohmic contact on p-type GaN using Ru overlayer

Area of Science:

• Materials Science
• Solid State Physics
• Semiconductor Device Fabrication

Background:

• Ohmic contacts are essential for efficient charge carrier injection in semiconductor devices.
• Developing low-resistance, high-reflectance ohmic contacts on p-type Gallium Nitride (GaN) is challenging but critical for optoelectronics.
• Existing methods often struggle to balance low resistivity, high reflectance, and surface morphology.

Purpose of the Study:

• To report a novel metallization scheme for creating high-performance ohmic contacts on p-type GaN.
• To investigate the effects of oxidation annealing on the contact properties.
• To optimize contact resistivity, reflectance, and surface morphology.

Main Methods:

• Fabrication of Ag-Cu alloy/Ru multilayer structures on p-type GaN.
• Annealing the contacts at 400°C in air ambient.
• Characterization of contact resistivity, reflectance, and surface morphology.

Main Results:

• Achieved a low contact resistivity of 6.2 x 10^-6 Ohms cm^2.
• Obtained high reflectance of 91% at 460 nm.
• Observed formation of an Ag-Ga solid solution due to Ga out-diffusion, lowering resistivity.
• Ru layer acted as a diffusion barrier, ensuring high reflectance and smooth surface.

Conclusions:

• The Ag-Cu alloy/Ru metallization scheme provides excellent ohmic contact properties for p-type GaN.
• Oxidation annealing is effective in reducing contact resistivity through Ga out-diffusion and solid solution formation.
• The Ru overlayer is crucial for maintaining high reflectance and surface quality by preventing excessive oxidation.