750 V Breakdown in GaN Buffer on 200 mm SOI Substrates Using Reverse-Stepped Superlattice Layers

Area of Science:

• Materials Science
• Semiconductor Physics
• Epitaxial Growth

Background:

• Gallium nitride (GaN) is a critical material for high-power and high-frequency electronics.
• Growing high-quality GaN on large-diameter substrates like silicon-on-insulator (SOI) presents challenges in managing stress and crystal defects.
• Existing GaN-on-Si buffer layers often suffer from high wafer curvature and lower breakdown fields.

Purpose of the Study:

• To develop and demonstrate an improved GaN buffer structure on 200 mm SOI substrates.
• To mitigate wafer bowing and enhance the crystal quality and electrical properties of GaN epitaxial layers.
• To enable the fabrication of high-performance GaN devices, such as D-mode HEMTs.

Main Methods:

• Epitaxial growth of GaN buffer using a reversed stepped superlattice (RSSL) structure on 200 mm SOI substrates.
• The RSSL buffer comprises two superlattice (SL) layers with varying Aluminum (Al) component ratios in reverse order.
• Characterization of wafer bow, crystal quality, breakdown voltage, and buffer dispersion.

Main Results:

• Achieved a well-controlled wafer bow ≤ ±50 µm for a 3.3 µm thick GaN buffer.
• Obtained good crystal quality of GaN layers due to the compliant nature of the SOI substrate.
• Demonstrated a breakdown voltage of 750 V for the 3.3 µm thick GaN buffer, with an estimated breakdown field strength of ~2.27 MV/cm.
• RSSL buffer exhibited low dispersion (<10%), suitable for device fabrication.
• Fabricated D-mode GaN HEMT showed an on/off ratio of ~10^9 and a breakdown voltage of 450 V.

Conclusions:

• The RSSL buffer on SOI substrates effectively manages tensile stress, leading to reduced wafer curvature and improved GaN crystal quality.
• The demonstrated GaN buffer structure offers superior breakdown field strength compared to GaN-on-Si.
• This approach is promising for the fabrication of high-performance, reliable GaN power devices on large-diameter SOI wafers.