Infrared and Raman spectroscopic investigation of thin films of AlN and SiC on Si substrates

摘要

A series of single AlN and SiC thin films as well as SiC/AlN double layers were investigated by FTIR spectroscopy (reflection and transmission) and by Raman microscopy. The films (100-1200 nm thick) were prepared by laser ablation on Si(111) substrates at a relatively low temperature (800 deg C) to prevent thermal decomposition of the nitride. Raman spectra showed the formation of nanocrystalline AlN films characterized by broad scattering regions between 200 and 900 cm~(-1) and a weak, broad band at 665 cm~(-1). Furthermore they revealed amorphous SiC (scattering between 200 and 960 cm~(-1)) with admixtures of amorphous carbon (scattering between 1300 and 1600 cm~(-1)). The SiC films had a strong absorption and extinguished Raman scattering of the deeper layers. The IR spectra confirmed the presence of finely distributed SiC and AlN by intense bands at 795 and 665 cm~(-1), respectively. The optical models of these layers indicated free charge carriers in the SiC and SiC/AlN films. The AlN component of the SiC/AlN double layers showed a dielectric function containing free charge carriers in addition to that of a single film. Raman microscopy allowed the study of the boundary region between single and double layers on the same sample.