Analysis of SiH and SiN vibrational absorption in amorphousSiNx:H films in terms of a charge-transfer model

Amorphous ${\mathrm{SiN}}_{\mathit{x}}$:H films were deposited at 300 °C by rf glow discharge of ${\mathrm{SiH}}_4$-${\mathrm{NH}}_3$ mixtures, and the SiH and SiN stretching absorption were investigated as a function of the N content x. From the x dependence of the absorption intensity, the bonding structure was decomposed into five bonding units without H atoms and those with H atoms, on the basis of a modified random-bonding model. For each bonding unit, the oscillator strength of the SiH absorption and the SiH and SiN bond lengths were estimated from the values of the additional partial charge on the Si, N, and H atoms by using Sanderson’s model. The peak wave numbers of the SiH and SiN absorptions were calculated by linking them to their respective bond-length values, a procedure which is based on an assumption that the force constant will be mainly controlled by the bond length. The effective SiH and SiN peak wave numbers for a given value of x, obtained as a statistical average of the calculated ones for individual bonding units, agreed well with the experimentally determined values. Also, peak shifts of the SiH absorption for various bonding units and those of the SiN absorption due to incorporation of SiH, SiN, and NH bonds are discussed in terms of the above charge-transfer model.