Measurements of Carrier Concentration, Mobility and Crystalline Properties Along the Growth Direction in MOCVD-Grown GaN-on-Sapphire by Cross-Section Raman Spectroscopy

GaN-on-sapphire structure is currently playing an important role in developing modern optoelectronic and electronic devices. Cross-sectional Raman scattering (RS) measurements were conducted along the growth direction of GaN-on-sapphire structures; the 4.0 μm R4 and 7.6 μm N7 layers were measured using step intervals of 0.5 μm and 1.0 μm, respectively. Characterization techniques, such as scanning electron microscopy, optical transmission and spectroscopic ellipsometry, have been applied to these GaN/sapphire structures and provide information on the crystalline properties of the two GaN films. Cross-sectional Raman measurements showed sample-dependent shifts in the fitted GaN E2(high) and E1(LO) peak positions. The fitted E2(high) peak positions were used to estimate the relative stress profiles, while spatial correlation model analysis provided model-dependent estimates of the effective phonon correlation lengths and damping constants. Longitudinal optical phonon–plasmon coupling fitting of the E1(LO) modes was used to estimate the carrier concentration and mobility. The distinctive findings may enhance the comprehension of GaN/sapphire and present valuable benchmarks for others within this field.