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

A series of single NN and SiC thin films as well as SiC/AlN double layers w ere investigated by FTIR spectroscopy (reflection and transmission) and by Raman microscopy. The films (100-1200 nm thick) were prepared by laser abla tion on Si(lll) substrates at a relatively low temperature (800 degrees C) to prevent thermal decomposition of the nitride. Raman spectra showed the f ormation of nanocrystalline ALN films characterized by broad scattering reg ions between 200 and 900 cm(-1) and a weal;, broad band at 665 cm(-1). Furt hermore they revealed amorphous SiC (scattering between 200 and 960 cm(-1)) with admixtures of amorphous carbon (scattering between 1300 and 1609 cm(- 1)). The SiC films had a strong absorption and extinguished Raman scatterin g of the deeper layers. The IR spectra confirmed the presence of finely dis tributed SiC and AIN by intense bands at 795 and 665 cm(-1), respectively. The optical models of these layers indicated free charge carriers in the Si C and SIC/AlN films. The AIN component of the SIC/AlN double layers showed a dielectric function containing free charge carriers in addition to that o f a single film. Raman microscopy allowed the study of the boundary region between single and double layers on the same sample. (C) 1999 Elsevier Scie nce B.V. All rights reserved.