# Defect Reduction in HEMT Epilayers on SiC Meta-Substrates

## TL;DR

This study shows how using specially designed 4H-SiC meta-substrates can significantly reduce defects in GaN layers, improving electronic device performance.

## Contribution

The novel use of patterned 4H-SiC meta-substrates to control and reduce threading dislocations in GaN epitaxy is demonstrated.

## Key findings

- A 54.96% reduction in threading dislocations was achieved using optimized pattern geometry.
- Dislocation bending and termination near meta-structured regions was confirmed via microscopy.
- An optimal pattern ratio exists for minimizing defect density in GaN epilayers.

## Abstract

Dislocation reduction in gallium nitride (GaN) epitaxial layers remains a critical challenge for high-performance GaN-based electronic devices. In this study, GaN epitaxial growth on newly-developed 4H-Silicon Carbide (SiC) meta-substrates was systematically investigated to elucidate the role of surface pattern geometry in modulating dislocation propagation. A series of truncated-hexagonal-pyramid meta-structures with a fixed array period and varying pattern ratios (R) were designed and fabricated to enable controlled tuning of the effective surface morphology. Atomic force microscopy confirmed comparable surface flatness for all samples after epitaxial growth. Cathodoluminescence analysis revealed a non-monotonic dependence of defect density on R, indicating the existence of an optimal pattern geometry. Among all configurations, the outstanding sample exhibited the lowest defect density, achieving a 54.96% reduction in threading dislocations (edge + mixed) compared with a planar reference. Cross-sectional transmission electron microscopy further confirmed a substantially reduced dislocation density and clear evidence of dislocation bending and termination near the meta-structured regions. These results demonstrate that geometry-engineered 4H-SiC meta-substrates provide an effective and scalable strategy for dislocation modulation in GaN epitaxy on SiC meta-substrates, offering a promising pathway toward advanced GaN power and RF devices.