Sub-resolution detectability of nanoscale surface defects in β-Ga2O3 enabled by phase-contrast microscopy

We quantitatively investigate the detectability of nanoscale surface defects in β-Ga2O3 using phase-contrast microscopy. Surface depressions with depths of ∼40–50 nm are shown to remain detectable even when their lateral dimensions are well below the diffraction limit. An analytical framework based on Gaussian defect profiles and diffraction-limited imaging theory accurately reproduces the observed detection boundary. The results demonstrate a general principle that defect detectability is governed by the phase signal integrated over the point spread function rather than by spatial resolution alone. This framework establishes a general principle for phase-based defect detection and provides practical guidelines for optimizing optical inspection systems for wide-bandgap semiconductors.