I. P. Vorona

Structural transformations and silicon nanocrystallite formation in SiOx films

The results of a comprehensive study by the methods of IR absorption, Raman scattering, photoluminescence (PL), and electron spin resonance (ESR) of SiOx films prepared by thermal evaporation of SiO in a vacuum are presented. The nature of structural transformations occurring on annealing the films is determined. Annealing in the temperature range 300–600°C gives rise to a PL band at 650 nm, presumably related to structural defects in SiOx film. Raising the annealing temperature further leads to healing of such defects and quenching of the PL band. Silicon precipitates pass from the amorphous to the crystalline state on being annealed at Tann=1100°C, which gives rise to a new PL band at 730 nm. ESR spectra of Pb centers were recorded at the interface between randomly oriented silicon nanocrystallites and SiO2.

Photoluminescence and paramagnetic defects in silicon-implanted silicon dioxide layers

Thermally grown SiO 2 layers on Si substrates implanted with Si‘ ions with a dose of 6]1016 cm~2 were studied by the techniques of photoluminescence, electron paramagnetic resonance (EPR), and low-frequency Raman scattering. Distinct oxygen-vacancy associated defects in SiO 2 and non-bridging oxygen hole centers were identified by EPR. The luminescence intensity in the 620 nm range was found to correlate with the number of these defects. The low-frequency Raman scattering technique was used to estimate the average size of the Si nanocrystallites formed after the implantation and thermal annealing at „’1100iC, which are responsible for the photoluminescence band with a maximum at 740 nm. The intensity of this band can be significantly enhanced by an additional treatment of the samples in a low-temperature RF plasma. ( 1999 Elsevier Science B.V. All rights reserved.

New insight on the interaction of self-activated and Mn-related emission centers in ZnS

The photoluminescence (PL) and PL excitation (PLE) spectra of undoped and thermally doped with Mn ZnS single crystals are studied. In the PL spectra, the bands caused by Mn-related and self-activated (SA) emission centers were observed. A number of narrow peaks whose intensity enhanced with increasing Mn content were found in the PLE spectra of SA emission. The same peaks were present in the PLE spectra of the Mn-related emission band. Some of these peaks were previously observed in the absorption spectra and attributed to Mn2+ ions. The appearance of Mn-related peaks in the PLE spectra of SA emission is explained by excitation transfer from the Mn2+ ions to SA emission centers. The conditions required for this transfer and possible mechanisms of the process are discussed.

Certain features of Ga diffusion in ZnS powders

Spectra of photoluminescence and electron spin resonance were investigated for ZnS powders annealed in the presence of metallic Ga with limited access of atmospheric air. Analysis of these spectra showed that there was no Ga impurity in the annealed ZnS powders. It was established that subsequent free access of air to annealed ZnS:Ga promotes active Ga introduction into the ZnS lattice. A mechanism of Ga diffusion in ZnS is suggested.