Optimization of Non-Alloyed Backside Ohmic Contacts to N-Face GaN for Fully Vertical GaN-on-Silicon-Based Power...

Area of Science:

• Materials Science
• Semiconductor Device Fabrication
• Gallium Nitride (GaN) Technology

Background:

• Development of fully vertical Gallium Nitride (GaN)-on-Silicon device technology is crucial for advanced electronics.
• Achieving reliable non-alloyed ohmic contacts on the N-polar n+-doped GaN backside layer is a key challenge.
• Poor ohmic contact quality is observed with as-deposited metal stacks on N-polar GaN after substrate removal.

Purpose of the Study:

• To optimize non-alloyed ohmic contacts on the N-polar n+-doped GaN backside layer.
• To investigate the effect of hydrochloric acid (HCl) treatment on contact resistance and material properties.
• To determine the optimal conditions for HCl treatment to achieve thermally stable, high-quality ohmic contacts.

Main Methods:

• Fabrication of patterned Transmission Line Model (TLM) structures using direct laser writing lithography.
• Accessing the N-polar n+-doped GaN backside layer by locally removing substrate and buffer layers.
• Application of HCl treatment prior to metallization under varied time and temperature conditions.
• Characterization using Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS).

Main Results:

• A 3-minute HCl treatment at 70 °C yielded optimal conditions for thermally stable, high-quality ohmic contacts.
• XPS analysis showed a decrease in Ga-O concentration after HCl treatment, indicating reduced oxidation.
• SEM revealed the formation of time-dependent pyramids on the N-face after HCl treatment, impacting contact quality.

Conclusions:

• Optimized HCl treatment is essential for improving non-alloyed ohmic contact quality on N-polar GaN.
• The N-polar GaN surface exhibits higher oxidation susceptibility compared to the Ga-polar face.
• Surface morphology changes, such as pyramid formation, due to HCl treatment influence ohmic contact performance.