Effect of mechanical stress on the absorption band tail of cubic boron nitride thin films synthesized by inductively coupled radio-frequency plasma chemical vapour deposition

摘要

Thin films of cubic boron nitride were deposited on silica and Si substrates by inductively coupled radio-frequency plasma chemical vapour deposition (IPCVD) technique using a B_2H_6 + N_2 + Ar gas mixture. Cubic phase formation was confirmed by glancing-angle X-ray diffraction studies, which showed reflections up to (311). Fourier-transform infrared (FTIR) spectra also indicated the predominantly cubic nature of the deposited films. The optical properties of the films were studied in the wavelength range 200-1000 nm. Both direct and indirect transitions were found to be present. Mechanical stress in the grain-boundary region of the films seems to contribute significantly to the optical absorption below the band gap. The intercrystalline barrier height (E_b) and the trap state density (Q_t) were obtained from an analysis of the effects of grain boundaries on the optical properties of the samples.