Comparative spectroscopic studies of MOCVD grown AlN films on Al2O3 and 6H–SiC
Abstract
A comprehensive spectroscopic study is reported for MOCVD (Metal organic chemical vapor deposition) grown AlN thin films prepared on sapphire (Al2O3) and 6H–SiC substrates. Impacts of substrate on the structural, surface and optical properties of AlN epilayers are meticulously appraised by using high resolution X-ray diffraction (HR-XRD), X-ray photoelectron spectroscopy (XPS), Raman scattering (RS), optical transmission (OT), spectroscopic ellipsometry (SE), photoluminescence (PL) and atomic force microscopy (AFM). Comparative results with different spectroscopic studies have revealed better crystalline quality of the AlN films grown on 6H–SiC than on Al2O3. For AlN/Al2O3 our extensive measurements have clearly uncovered a significant influence of the substrate on film's surface roughness, dislocation density, grain size, micro strain and the incorporation of oxygen on its surface. Careful analysis of the temperature-dependent RS results have shown an appealing phenomena of the existing biaxial stress in AlN films altering from compressive to tensile stress as the temperature is increased from 80 K to 800 K. This effect exhibits higher temperature inflection point for AlN/Al2O3 film than AlN/6H–SiC.