Confocal Raman spectroscopy characterization of heteroepitaxial interfacial stress of GaN on sapphire substrate

Confocal Raman spectroscopy permits the nondestructive, depth-resolved quantification of interfacial stress in semiconductor heterostructures, which has an adverse impact of subsequent semiconductor device processing. In this study, a high-axial-resolution measurement system based on confocal Raman spectroscopy is developed for interfacial stress analysis. The critical parameters are systematically investigated to achieve superior axial tomographic capability and excellent signal-to-noise ratio, including confocal configuration, aperture size, objective numerical aperture, and laser wavelength. A reliable framework for assessing interfacial stress is thereby established. Using the E2H Raman shift as the primary indicator for stress quantification, quantitative analysis is performed on undoped, n-doped, and p-doped GaN layers. The relationship between doping type and interfacial stress is clarified with high precision. Additionally, Raman stress mapping is performed on trench-patterned GaN samples. Process-induced stress distributions are visually revealed, providing key technical insights for optimizing semiconductor processing strategies. This work will provide valuable experimental benchmarks and practical guidelines for stress engineering and reliability optimization in GaN-based high-frequency and high-power electronic devices.