SiN_x/(Al,Ga)N interface barrier in N-polar III-nitride transistor structures studied by modulation spectroscopy

Area of Science:

• Semiconductor physics
• Materials science
• Device engineering

Background:

• N-polar III-nitride high electron mobility transistors (HEMTs) are crucial for power electronics.
• Understanding the built-in electric field and carrier behavior in scaled HEMTs is essential for device optimization.
• In-situ silicon nitride (SiNx) capping is a common technique in HEMT fabrication.

Purpose of the Study:

• To analyze the built-in electric field in the GaN channel of N-polar HEMTs with scaled channel thickness.
• To investigate the sheet carrier densities (n_s) in these scaled structures.
• To correlate experimental findings with theoretical models and identify the cause of unexpected carrier behavior.

Main Methods:

• Contactless electroreflectance (CER) spectroscopy was employed to probe the electronic properties.
• Numerical calculations were performed to model the electric field and carrier distributions.
• Experimental data on electric field and sheet carrier density were compared with theoretical predictions.

Main Results:

• Experimental built-in electric field values were obtained and compared with theoretical curves.
• Sheet carrier densities were evaluated, showing a gradual decrease with decreasing channel thickness as expected.
• A sudden, unexpected drop in sheet carrier density was observed for very thin channels.

Conclusions:

• The sudden loss of charge in thin N-polar HEMT channels is attributed to a shift in the SiNx/AlGaN interface Fermi level.
• This finding highlights the critical impact of interface properties on carrier confinement in scaled III-nitride devices.
• The study provides valuable insights for the design and fabrication of advanced N-polar HEMTs.