Deposition of hafnium silicate films with various hafnium contents was tried by plasma-enhanced chemical vapor deposition using tetraethoxysilane and a hafnium alkoxide. From x-ray photoelectron spectroscopy, the deposited films are confirmed to be silicate with Hf–O–Si bonds but without any Hf–Si bonds. The permittivity calculated from the capacitance of the accumulation layer increases monotonically with an increase in the hafnium content, whereas the optical band gap energy estimated from vacuum ultraviolet absorption spectra decreases. Similar results were obtained from zirconium silicate films deposited using tetraethoxysilane and a zirconium alkoxide. If we compare the films with the same hafnium or zirconium content, the hafnium silicate exhibits a higher permittivity and a larger band gap energy than the zirconium silicate.

Photochemical reactions related to the Ge lone-pair center ͑GLPC͒ that are induced by KrF excimer laser photons in H 2 -loaded Ge-doped SiO 2 glass have been investigated. Without the H 2 loading, the Ge electron center ͑GEC͒ and the positively charged GLPC were induced by the laser irradiation. In the H 2 -loaded sample, the GEC, the Ge EЈ center, and the germyl radical ͑GR͒ were induced by the irradiation, while the positively charged GLPC was not observed after the irradiation. If the H 2 -loaded sample was thermally annealed after the photon irradiation, the concentration of the photo-induced GEC decreased monotonically with an increase in the annealing temperature. On the other hand, the concentration of the GR increased up to the annealing temperature of 160°C, and it decreased at higher temperatures. Without the pre-irradiation, the induction of the GR was not observed even in the H 2 -loaded sample. From these results, it is concluded that the positively charged GLPC is terminated with a hydrogen atom in the H 2 -loaded sample and then becomes the GR by trapping an electron thermally released from the GEC. ͓S0163-1829͑99͒05631-3͔ PHYSICAL REVIEW B 15 AUGUST 1999-I VOLUME 60, NUMBER 7 PRB 60 0163-1829/99/60͑7͒/4682͑6͒/$15.00 4682

Structural differences between deuterated and hydrogenated silicon nitride/oxynitridePhotoluminescence ͑PL͒ measurements were performed on a series of hydrogenated amorphous silicon oxynitride and silicon nitride films with different nitrogen contents deposited by plasma-enhanced chemical-vapor deposition. From the PL and PL excitation spectra, the Urbach energy of the sample is found to be proportional to its PL half-maximum width, regardless of whether the sample is silicon oxynitride or silicon nitride. Time-resolved PL measurements showed that PL peak energy varies with time after the excitation, showing a systematic dependence on the chemical composition in the two materials. That the PLs observed in the two materials have very similar characteristics regardless of the presence of oxygen strongly indicates that the PLs result from the same chemical structure, more specifically Si-N bonds, and that the two materials have similar band-tail states associated with the static disorder. In the two materials, it is found that the electrons and holes photoexcited into such band-tail states recombine first through an excitonlike recombination process and then through a radiative tunneling recombination process.

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