Comparative Spectroscopic Study of Aluminum Nitride Grown by MOCVD in H2 and N2 Reaction Environment

We report a comparative spectroscopic study on the thin films of epitaxial aluminum nitride (AlN) on basal plane sapphire (Al2O3) substrates grown in hydrogen (H-2) and nitrogen (N-2) gas reaction environments. AlN films of similar thicknesses (similar to 3.0 mu m) were grown by metal-organic chemical vapor deposition (MOCVD) for comparison. The impact of the gas environment on the AlN epilayers was characterized using high-resolution X-ray diffraction (HR-XRD), X-ray photoelectron spectroscopy (XPS), Raman scattering (RS), secondary ion mass spectroscopy (SIMS), cathodoluminescence (CL), atomic force microscopy (AFM), and scanning electron microscopy (SEM). The study showed that AlN layers grown in a N-2 environment have 50% less stress (similar to 0.5 GPa) and similar total dislocation densities (similar to 109/cm(2)) as compared to the films grown in a H-2 environment. On the other hand, AlN films grown in a H-2 gas environment have about 33% lesser carbon and 41% lesser oxygen impurities than films grown in a N-2 growth environment. The possible mechanisms that influenced the structural quality and impurity incorporation for two different gas environments to grow AlN epilayers in the MOCVD system on sapphire substrates were discussed.