Stress and doping analysis of low n-doped GaN layers on various substrates by micro-Raman mapping

In this work, using micro-Raman spectroscopy mapping, we propose a methodology to separate the stress effect from the n-doping effect on A1LO and E2H GaN phonon modes frequency for low n-doped (<1017 cm−3) GaN layers grown on various substrates (GaN, sapphire, and silicon). This methodology shows a linear relation between the two phonon modes, in which the slope corresponds to GaN biaxial stress coefficients ratio KA1LOB/KE2HB and is 0.76 ± 0.01. Our value may act as a useful guideline for selecting or refining KE2HB and KA1LOB values. Samples that are mainly biaxially stressed show good agreement with the linear relation independently of the substrate. As for GaN/GaN samples, the change of slope indicates that layers are predominantly under dislocation-induced stress. However, independently of the substrate, the y-intercept increases with the n-carrier concentration, which provides a qualitive estimation of the net doping.