Elliptically polarized light-induced second harmonic generation in SiNxOy

Elliptically polarized photoinduced second harmonic generation (PISHG) in SiNxOy films was studied for specimens with different nitrogen to oxygen (N/O) ratios. As a source for the photoinducing light, we used a nitrogen Q-switched pulse laser at a wavelength of 337 nm. YAG:Nd pulse laser (lambda = 1.06 mu m; W = 30 MW; tau = 10-50 ps) was used to measure the PISHG. All measurements were made in a reflected light regime. We found that the output PISHG signal was dependent on the N/O ratio and the film thickness. The SiNxOy films were synthesized using a technique of chemical evaporation at low pressures. Films with thickness varying between 10 and 30 nm and with an N/O (nitrogen/oxygen) ratio between 0 and 1 were obtained. The stochiometry of these films was measured after their deposition on Si[111] substrates by using an extended X-ray absorption fine structure (EXAFS) method. Distances between O-Si and N-Si atoms for different N/O ratio and film thickness were determined by data fitting analysis. Electrostatic potential distribution at the Si[111]-SiNxOy interfaces was calculated. Comparison of the experimentally obtained and quantum chemically calculated PISHG data are presented. High sensitivity of eliptically-polarized PISHG to the N/O ratio and film thickness is demonstrated. The role of the electron-phonon interactions in the dependencies observed is discussed. We have shown that the PISHG method has higher sensitivity than the traditional EXAFS spectroscopic method for films with an N/O ratio higher than 0.50. (C) 2000 Elsevier Science B.V. All rights reserved.