Comparative study of extended free‐volume defects in As‐ and Ge‐based glassy semiconductors: theoretical prediction and experimental probing with PAL technique

Abstract

The role of spatially‐extended defect configurations in As‐Se and Ge‐Se glasses is identified using available theoretical predictions and positron annihilation lifetime spectroscopy as an experimental tool. It is shown that compositional trends in average positron lifetime do not coincide with molar volume evolution in the glasses of corresponding binary systems. The heteropolar As‐Se covalent bonds are shown to affect the positron trapping modes more efficiently, than geometrical voids responsible for compositional deviation in molar volume. The same tendency is observed for Se‐rich Ge‐Se glasses. However, the Ge‐rich glasses in so‐called pseudo‐self‐organization domain, demonstrate an opposite trend in a favour of molecular clustering of edge‐ and corner‐shared tetrahedral units. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Effect of rare-earth doping on the free-volume structure of Ga-modified Te20As30Se50glass

“…Let's clarify physical meaning of these structural reconfiguration processes grounded on previous results for similar chalcogenide glass-forming systems. [20][21][22][26][27][28][29][30] Thus, it is well justified that among huge diversity of expected positron trapping sites possible in different ChG matrices, the preferential process of positron capturing is defined by extended freevolume defects in the nearest vicinity of chalcogen atoms neighboring with main glass-forming structural units (network-composing polyhedrons). [26][27][28][29][30] In view of extra-low two-fold coordination and strong directionality of covalent bonding, the chalcogen atoms form low-electron density spaces, termed also as bond free solid angles (BFSA) by Kastner.…”

PAL spectroscopy of rare-earth doped Ga–Ge–Te/Se glasses

“…The most essential growing effect in 2 lifetime from 0.346 ns to 0.356 ns is also caused in this Ga 10 (Table 1). Let's clarify physical meaning of this process and give its possible explanation in terms of known microstructure models developed for positron trapping in ChG [17,[28][29][30][31][32][33][34].…”

Free-volume correlations in positron-sensitive annihilation modes in chalcogenide vitreous semiconductors: on the path from illusions towards realistic physical description

“…(2) was not the best to fit the known experimental data in the probed polymers for small positron lifetimes  2 and void radii R (where Ps does not appear because of geometrical constraints [1,8,9]), it was proposed to replace it by the simplified linear equation:…”

“…Recently, this method has been employed even for such complicated disordered solids as chalcogenide vitreous semiconductors (ChVS) [3][4][5][6][7][8][9][10]. These glassy-like alloys of chemical elements from IV-V groups of the Periodic table (typically As, Ge, Sb, Bi, etc.)…”

“…Thus, in [23], the modified sequent  3 - 2 -R correlation was utilized as a basis of the generalized void-size-determination procedure for a wide range of materials, involving molecular substrates, such as polymers, as well as inorganic disordered solids like ChVS. Ignoring the principal difference in the chemical nature of these materials led to evidently misleading conclusion on expected positron trapping void volumes, which occur to be in apparent contradiction with proved experimental data for a great variety of ChVS [3][4][5][6][7][8][9][10]. The time is come to analyze critically these discussible diversities, asking a simple question: "How far can we really go with free-volume parameterization in amorphous semiconductors such as ChVS aided by PAL technique?".…”