Development and analysis of thick GaN drift layers on 200 mm CTE-matched substrate for vertical device processing

Area of Science:

• Materials Science
• Semiconductor Physics

Background:

• Advancements in Gallium Nitride (GaN) epitaxy are crucial for next-generation power electronics.
• Vertical GaN power devices offer superior performance but require thick, high-quality epitaxial layers.
• Large-diameter wafer processing is essential for cost-effective manufacturing.

Purpose of the Study:

• To report the epitaxial growth of thick GaN layers on engineered substrates for vertical power devices.
• To investigate the electrical characteristics and breakdown mechanisms of these devices.
• To assess the feasibility of CMOS-compatible processing for GaN power devices.

Main Methods:

• Epitaxial growth of 8.5 µm GaN on 200 mm polycrystalline AlN core substrates.
• Characterization using diode test structures, conductive Atomic Force Microscopy (cAFM), and scanning transmission electron microscopy (STEM).
• Analysis of leakage current using one-dimensional hopping conduction modeling.

Main Results:

• Achieved hard breakdown voltages greater than 750 V in diode test structures.
• Identified impurity/metal diffusion into threading dislocations as a limiting factor for breakdown voltage.
• Dislocation core structure (double 5/6 atom configuration) and leakage contribution were analyzed.
• Hopping conduction model showed good agreement with experimental leakage data.

Conclusions:

• Successful epitaxial growth of thick GaN layers on large-diameter engineered substrates is demonstrated.
• Understanding dislocation-related leakage is key to optimizing vertical GaN power devices.
• This work provides insights into the potential and challenges of fabricating GaN devices on large wafers for CMOS compatibility.