D. Arsova

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.

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.

Stability of amorphous Se/Se100−xTex multilayers: A Raman study

The Raman spectra of amorphous Se/Se100−xTex multilayers (AMLs) of various compositions and sublayer thicknesses have been measured at room and low temperature (38 K) with the aim to assess the thermal and absorption effects of laser illumination on the structural stability of the AMLs. Under thermal treatment at room temperature (mediated by increasing gradually the power of the probing laser line), the AML stability (manifested by the rate of Se crystallization) increases with decreasing Se100−xTex sublayer thickness and with decreasing Te content. However, in single layers (2 μm thickness) of Se100−xTex, we have observed the opposite effect, that is, the stability of single layers increases with increasing Te content. This apparent contradiction is explained in terms of thermodynamic energy considerations stated previously [K. Tanaka et al., Mater. Res. Soc. Symp. Proc. 118, 343 (1988)] and of a higher crystallization temperature of Se sublayers in the AMLs than that of bulk Se of the single layer. In ...

Photoinduced anisotropy in photobleached Ge–As–S films

Abstract Linear optical dichroism and birefringence induced by linearly polarized light were studied in the photobleached optically isotropic three-component GexAs40−xS60 films. The anisotropy can be erased by nonpolarized or circularly polarized light. Multiple reorientation under the action of linearly polarized light with orthogonal orientation of the electrical vector was investigated. The anisotropy relaxes gradually in the dark with a large time constant. The sign of dichroism was the same as in the binary As–Se and As–S photodarkened chalcogenide films. Therefore, the inducing polarized light always decreases the absorption of the light polarized parallel to itself. Photodarkening instead of photobleaching was observed in annealed films. Annealing resulted also in a strong decrease of photoinduced anisotropy that is different from the behaviour of binary chalcogenide films.

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.

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.

Photoinduced changes in amorphous chalcogenide films, modified at low temperatures

Abstract The selective solubility of amorphous As2Se3 and GeS1.5 films modified by means of co-evaporation with In or Ga at low substrate temperatures was investigated. The photoinduced change of the solubility of these films is more pronounced in comparison with films of the same composition but deposited at higher substrate temperatures. The optimum impurity concentrations and substrate temperatures at which the modified films demonstrated maximum photoinduced changes of the dissolving rate were specified as about 5 at.% In at a −60°C substrate temperature for As2Se3 and about 10 at.% In or Ga at −50°C for GeS1.5. These films may be promising as non-silver negative photoresists.

Current-voltage characteristics of thin Ge2Sb2Te5 films taken using a measuring circuit with a current source

The measuring circuit with a voltage generator, which is traditionally used for studying electric properties of glasslike semiconductors, is compared with an alternative version using a current generator. The results obtained in the latter case reflect the interrelation between the memory formation effect and changes in the electrical parameters more comprehensively. A new electric parameter, viz. hold voltage Uhold, which has not been described earlier, is introduced. The relation between Uhold and the memory formation process during the phase transition is established. The effect of emergence of oscillations in the current-limiting regime in the conduction channel in the film is detected.

A comparative raman study of the local structure in (Ge2S3) x (As2S3)1-x and (GeS2) x (As2S3)1−x glasses

The Raman spectra of glasses in the ternary (Ge2S3)x(As2S3)1−x and (GeS2)x(As2S3)1−x systems are reported. It is shown that the degree of disorder in the (Ge2S3)x(As2S3)1−x glasses increases with an increase in the Ge content. The differences in the spectra of glasses with the same molar content of As2S3 are discussed in terms of the changes occurring in the local structure due to deviations from the stoichiometry. The observed changes in the intensity of the boson peak indicate changes in the medium-range order structure of the glasses under study.