Different substrate structures affect the substitution efficiency of Al atoms in AlxGa1−xN epitaxial films

Abstract

Through XRD analysis and xrayutilities fitting, this paper investigates the structural parameters of AlxGa1−xN(AlGaN) epitaxial layers grown on both free-standing GaN (FS-GaN) substrates and GaN templates (4.5 um GaN on Sapphire), including thickness and Al composition. These parameters determine the conductivity performance of GaN high electron mobility transistor devices. Under the same growth conditions, the Al composition in the AlGaN epitaxial layer grown on FS-GaN substrates is lower, but the thickness (growth rate) is higher, indicating a relatively weaker efficiency of Al substitution for Ga. This trend remains within a large range of trimethylgallium input ratios of 20%–40%. By analyzing and demonstrating the various differences between the two substrates, it can be concluded that the misorientation angle and threading dislocation density of the GaN layer have a high correlation with the efficiency of Al substitution, while the stress of the GaN layer and the temperature of the substrate surface show no significant correlation.