Characterization of individual threading dislocations in GaN using ballistic electron emission microscopy

Area of Science:

• Materials Science
• Solid State Physics
• Semiconductor Physics

Background:

• Threading dislocations (TDs) in Gallium Nitride (GaN) films are critical defects affecting electronic properties.
• Previous research suggested the presence of fixed negative charge at TDs, influencing device performance.
• Accurate characterization of charge distribution at TDs is essential for advanced GaN-based electronics.

Purpose of the Study:

• To quantify fixed negative charge at threading dislocations in molecular beam epitaxy grown GaN films.
• To investigate the spatial distribution and magnitude of charge associated with TDs.
• To determine if local piezoelectric fields contribute to surface charge at TDs and step edges.

Main Methods:

• Utilized ultrahigh vacuum ballistic electron emission microscopy (UHV-BEEM).
• Achieved approximately 3 nm spatial resolution and approximately 10 meV local barrier resolution.
• Analyzed charge at specific TD structures and GaN step edges.

Main Results:

• No indication of fixed negative charge was found at specific TD structures.
• A conservative upper limit of approximately 0.25 e(-) per c-axis unit cell for negative charge was established.
• Evidence of positive surface charge was observed at TDs and GaN step edges.

Conclusions:

• The study contradicts some prior findings regarding negative charge at TDs in GaN.
• Observed positive surface charge suggests a role for local piezoelectric fields at TDs and step edges.
• These findings have implications for understanding and mitigating defect-related effects in GaN devices.