We investigate the effects of finite off-normal incidence on the polarized infrared reflectivity spectra of hexagonal boron nitride films deposited on Si substrates by radio frequency plasma enhanced chemical vapor deposition, using B2H6 (1% in H2) and NH3 gases. The experimental observation of a sharp structure associated to the coupling of the incident light with the LO component of the twofold stretching mode, and the absence of similar coupling effects with the LO component of the bending mode, indicates that the c-axis is parallel to the film surface. We also show that the infrared spectra are not modified when one rotates the sample perpendicularly to the growth direction. Therefore, we conclude that the principal axis of the polycrystalline boron nitride films is randomly oriented within the plane parallel to the film surface. Finally, we show that these optical results are in full agreement with high resolution transmission electron microscopy studies. © 1997 Elsevier Science S.A.
- BN films
- Polarized IR reflection spectroscopy
- R.f. Plasma CVD