Vertical Leakage in GaN-on-Si Stacks Investigated by a Buffer Decomposition Experiment

Area of Science:

• Materials Science
• Semiconductor Physics
• Electrical Engineering

Background:

• Vertical leakage and breakdown are critical limitations in Gallium Nitride-on-Silicon (GaN-on-Si) power devices.
• Understanding the role of individual buffer layers is essential for optimizing device performance and reliability.

Purpose of the Study:

• To investigate the origin of vertical leakage and breakdown mechanisms in GaN-on-Si epitaxial structures.
• To elucidate the specific contributions of the nucleation layer (AlN), AlGaN buffer, and C-doped GaN (C:GaN) to device performance.

Main Methods:

• Sequential growth of three distinct GaN-on-Si structures: AlN/Si, AlGaN/AlN/Si, and C:GaN/AlGaN/AlN/Si.
• Analysis of vertical current-voltage (I-V) characteristics and breakdown fields.
• Investigation of charge trapping phenomena within the buffer layers.

Main Results:

• The AlN layer on silicon exhibits a low breakdown field (3.25 MV/cm) due to defects, with negative charge trapping observed.
• Incorporating AlGaN reduces defect density and leakage uniformity.
• The C:GaN/AlGaN/AlN/Si structure achieves a breakdown voltage exceeding 800 V.
• Positive charge trapping at the GaN/AlGaN interface in the C:GaN layer was identified as a key factor for improved breakdown.

Conclusions:

• Each buffer layer plays a distinct role in determining vertical leakage and breakdown characteristics.
• Defects in the AlN layer are primary leakage paths.
• Carbon-doped GaN is crucial for achieving high breakdown voltages through controlled positive charge storage.