Visualization of GaN surface potential using terahertz emission enhanced by local defects

Area of Science:

• Materials Science
• Solid State Physics
• Semiconductor Device Physics

Background:

• Wide-gap semiconductors offer superior performance for energy-efficient power devices compared to traditional materials.
• Understanding surface and interface electrical properties is critical for stable and reliable wide-gap semiconductor device fabrication.
• Gallium Nitride (GaN) is a key wide-gap semiconductor with significant potential in power electronics.

Purpose of the Study:

• To visualize terahertz (THz) emission from the surface of GaN.
• To investigate the relationship between THz emission and surface defects.
• To establish a method for evaluating surface potential and non-radiative defects in GaN.

Main Methods:

• Excitation of GaN surface using ultraviolet femtosecond laser pulses.
• Measurement and analysis of terahertz (THz) emission.
• Correlation of THz emission with yellow luminescence and defect sites.

Main Results:

• Terahertz (THz) emission from GaN surface was successfully visualized.
• THz emission intensity was found to be enhanced by defects associated with yellow luminescence.
• The enhancement is attributed to modifications in the surface depletion layer band structure due to trapped electrons at defect sites.

Conclusions:

• Laser-induced THz emission can effectively detect surface potential in GaN.
• This method allows for the evaluation of non-radiative defects, which are not detectable by photoluminescence.
• The findings contribute to the development of normally-off GaN devices for improved power efficiency.