E. Skordeva

Optical properties of Ge-As-S thin films

Based on two independent methods, the spectral dependence of the refractive index n and the absorption coefficient α in the regions of weak and strong absorption is calculated. Conclusions are drawn concerning the influence of variation in the composition, technology and treatment on the films optical parameters; the relation is also shown to the films selective solubility.

Topological threshold in GexAs40−xSe60 glasses and thin films

Abstract Composition dependences of the mean atomic volume of glasses of the GexAs40−xSe60 system, as well as of the optical bandgap, solubility, and their changes on irradiation in thin films of the same system, are measured. It is shown that there is a topological threshold at an average coordination number Z≈2.67 both in glasses and in thin films of this chalcogenide system, similar to the transition observed in GexAs40−xS60 glasses and films.

Structure and physical properties of the glassy As2S3Gex system

Abstract Spectroscopical and structural investigations directly reveal the presence of those structural units which were predicted by Myuller and coworkers to form the continuous network of As-S-Ge glasses. After refining Myullers model to some extent, the variation with x of several physical properties (density, microhardness, electrical dark conductivity, photoconductivity, optical gap and first-neighbour coordination) in the whole series of As 2 S 3 Ge x glasses can be either understood qualitatively or even calculated quantitatively with the aid of additivity laws.

Effect of Co60 γ-irradiation on the optical properties of As-Ge-S glasses

Abstract The influence of Co 60 γ-irradiation on the optical properties of chalcogenide semiconducting glasses from As 2 S 3 –Ge 2 S 3 cut-section is analyzed taking into account the accompanying spontaneous thermal annealing of the samples in the irradiation chamber. It is established that essential thermal heating of the investigated glasses during high-doses irradiation leads to the rough changes in compositional dependences of radiation-induced total (unrelaxed) and static (relaxed) optical effects. An attempt to describe dose dependence of the observed optical changes is made on the basis of stretched–exponential relaxation function.

Irreversible and reversible changes in band gap and volume of chalcogenide films

Abstract Irreversible and reversible changes induced by illumination and/or annealing of thin evaporatively deposited Ge–As–S films at normal incidence are studied. Attention is paid to the volume (thickness) changes and their correlation with the changes induced in the band gap of the ternary and binary chalcogenides. The revealed dependences are compared to that obtained for obliquely deposited chalcogenide films and substantial differences have been found.

Compositional Dependences of Some Optical and Electrical Properties of the GexAs40—xSe60 System

The compositional dependences of the Urbach energy E U , dark conductivity and its activation energy have been measured in the Ge x As 40-x S 60 system. Two regions of Eu increase with different steepness and a shoulder at x = 20 to 27 have been observed. A well expressed minimum of the dark conductivity at x = 27 to 30 corresponding to an average coordination number Z ≃ 2.7 has also been found. The observed peculiarities in the compositional dependences studied are connected with the topological phase transition expected at Z = 2.67 as well as with compositionally induced changes in the short-range order.

Radiation-stimulated changes in the transmission of chalcogenide glasses of As2S3−Ge2S3

The radiative-optical properties of chalcogenide glass-like semiconductors of the As2S2−Ge2S3 system in the region of a topological 2D-3D-phase transition are investigated. It is shown that γ-irradiation of samples by an absorbed dose of 4.4 · 106 Gy leads to a longwave shift of their optical-transmission edge in the spectrum. The effect observed depends on the structural type of the glasses investigated and changes considerably near the 2D-3D-phase transition. Two components of the transmission-edge shift are detected: a static component, which remains unchanged for a long time after irradiation of the samples, and a dynamic one, which gradually fades in 2–3 months. It is suggested that the microstructural mechanism of these changes is attributable to processes of coordination defect formation in the structural skeleton of the samples.

radiation-induced effects in Ge-As-S chalcogenide glasses

The radiation-optical properties of vitreous semiconductors in the Ge-As-S system are studied near the 2D-3D topological phase transition. The results obtained are interpreted within the framework of the model of coordination defect centers, which are characteristic of chalcogenide vitreous semiconductors.

Photo-induced softening and hardening in Ge–As–S amorphous films

Abstract Hardness, X-ray diffraction and transmission as well as infrared reflection measurements on virgin and ultraviolet (UV)-irradiated amorphous films of the GexAs40−xS60 system have been performed. The UV light induces film softening for x 19. The structure remains amorphous but the distance characteristic of medium range order decreases for x 19. Photo-contraction of the films (up to ∼12%) has been revealed from IR spectra and X-ray transmission experiments. A main effect of UV light is the release of sulphur.

New features of the medium range order in GexAs40−xSe60 glasses

Abstract A stable structural anisotropy, strongly dependent on the azimuthal angle of Ge x As 40− x Se 60 bulk glasses, is observed by X-ray diffraction. The anisotropy is revealed in both first sharp diffraction peak (FSDP) and pre-FSDP. The topological phase transition in this powder glasses system is confirmed.