What are the challenges in achieving high breakdown voltage in GaN devices?

Achieving high breakdown voltage in GaN devices is crucial for their efficient operation and reliability. However, several challenges must be addressed to realize this goal. Let%27s delve into the details:

1. Lateral vs. Vertical Devices:
- Lateral GaN devices (such as GaN high-electron-mobility transistors or HEMTs) face limitations due to area occupancy and surface trap-related reliability concerns.
- Vertical GaN devices, on the other hand, do not require increased chip size for higher breakdown voltage.
- Vertical GaN devices achieve higher breakdown voltage by increasing the thickness of the drift region while maintaining a compact chip size.
- Moving the peak electric field from the surface into the GaN bulk minimizes surface trapping effects and dynamic ON resistance in vertical devices.

2. Surface Traps and Reliability:
- High breakdown voltage in lateral GaN devices is hindered by surface traps.
- Surface traps can lead to reliability issues, affecting long-term device performance.
- Addressing surface trap-related degradation is essential for achieving reliable high-voltage operation.

3. Dislocation Density:
- High dislocation density in GaN crystals affects breakdown voltage.
- Dislocations create localized electric fields, leading to premature breakdown.
- Reducing dislocation density improves material quality and reliability.

4. Doping Optimization:
- Optimizing the doping level in the GaN device stack is critical.
- Proper doping profiles influence breakdown voltage and overall device performance.
- Balancing doping concentration with other material parameters is challenging.

5. Alternative Substrates:
- Researchers explore large-diameter substrates for vertical GaN fabrication.
- Engineered substrates, such as those with matched coefficients of thermal expansion (CTE), pave the way for industrial-scale production of vertical GaN devices.

6. Alternative Epitaxy Techniques:
- Coalescence epitaxy of GaN-on-silicon is an alternative technology path.
- It enables thick drift layers with very low dislocation density.
- Exploring novel epitaxy methods enhances breakdown voltage capabilities.

In summary, achieving high breakdown voltage in GaN devices requires addressing surface traps, dislocation density, doping optimization, and exploring alternative substrates and epitaxy techniques¹²³⁴. These challenges remain active areas of research as GaN technology continues to evolve.

(1) Vertical GaN Devices: Process and Reliability - arXiv.org. https://arxiv.org/pdf/2107.02469.
(2) Review of Recent Progress on Vertical GaN-Based PN Diodes. https://link.springer.com/article/10.1186/s11671-021-03554-7.
(3) GaN-based vertical power devices - Massachusetts Institute of Technology. https://dspace.mit.edu/handle/1721.1/112002.
(4) Micromachines | Free Full-Text | A Brief Overview of the Rapid ... - MDPI. https://www.mdpi.com/2072-666X/14/4/764.
(5) GaN power devices: current status and future challenges. https://iopscience.iop.org/article/10.7567/1347-4065/ab12c9/pdf.

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