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Coordination Defects and Their Respective Role on the Photoinduced Changes in Ge-Sb-Se and Related Chalcogenide Thin Films

Authors: Halenkovič Tomáš | Nazabal Virginie | Kotrla Magdaléna | Baillieul Marion | Gutwirth Jan | Němec Petr

Year: 2023

Type of publication: ostatní - přednáška nebo poster

Page from-to: nestránkováno

Titles:

Language	Name	Abstract	Keywords
eng	Coordination Defects and Their Respective Role on the Photoinduced Changes in Ge-Sb-Se and Related Chalcogenide Thin Films	Time evolution of the absorption coefficient in amorphous Ge-Sb-Se chalcogenide thin films upon cw-laser irradiation of a near-bandgap energy revealed variety of photoinduced changes in these materials. These include shift of the absorption edge of both positive (i.e., photobleaching, PB) and negative (i.e., photodarkening, PD) sign depending on the composition, structure, sample preparation and its history. Typically, irradiation of annealed films leads to reversible PD process. As-deposited films show rather complex behavior upon irradiation as the fast PD usually precedes the long-term effect of PB. The origin of these photostructural changes is closely related to defective states in an amorphous matrix. The structure of these materials is dominated by [GeSe4/2] tetrahedral units connected by corners and edges, accompanied with [SbSe3/2] pyramidal units and defective ethane-like [Ge2Se6/2] units. Even in stoichiometric compositions the portion of homopolar (wrong bonds) exists. Upon the thermal annealing the ratio between corner shared and edge shared tetrahedra changes, number of Ge-Ge homopolar bonds in ethane-like units decreases with the indication of selenium atoms consumption from Se– Se dimers and Sen short chains. These structural changes seem to be responsible for a transition from the PB effect in as-deposited to reversible PD in annealed thin films. Generally, homoto heteropolar bond conversion is regarded to be a major cause of the absorption edge shift upon irradiation. Moreover, the presence of lone-pair electrons predetermines the existence of charged defects (charged dangling bonds). Related to these, the valence alternation pair (VAP) model was proposed for pnictogen containing chalcogenide glasses, typically As2S3 or As2Se3, and describes the existence of defect pairs deviating from normal bonding states. In present work we attempt to clarify processes behind the photostructural changes in Ge-Sb-Se and related materials attributed to