Role of Ge:As ratio in controlling the light-induced response of a-GexAs35−xSe65 thin films

Abstract

In this paper, we present interesting results on the quantification of photodarkening (PD), photobleaching (PB) and transient PD (TPD) in a-GexAs35−xSe65 thin films as a function of network rigidity. Composition dependent light-induced responses of these samples indicate that there exist two parallel competing mechanisms of instantaneous PD arising from the As part of the network, and PB arising from the Ge part of the network. Raman spectra of the as-prepared and illuminated samples provide first direct evidence of the light-induced structural changes: an increase in AsSe3/2 pyramidal and GeSe4/2 corner-sharing tetrahedra units together with new Ge-O bond formation and decrease in energetically unstable edge sharing GeSe4/2 tetrahedra. Importantly, for a fixed Se concentration, Ge:As ratio plays the critical role in controlling the net light-induced response rather than the much believed rigidity of the glassy network.

Dual Effects of Photo-Darkening and Photo-Bleaching in Ge-Se Films

“…2 suggests that the PB effect is much slower than the PD. One of the reasons of the PB effect can be further homopolar bond breaking, occurring in a quite limited fashion, compared to the homopolar bonds reduction related to the PD process, similarly to the results reported in [22,24]. The ratio of Raman peak areas of the building blocks is quite close to that observed for relaxed bulk material with the same composition [29].…”

“…The dual action of light was shown earlier in Ge-As-S [22,23] and in Ge-As-Se [24] films. In essence, this shows the reversibility of the processes for which Elliott has created a unified model [25].…”

Nanosecond light-induced transient absorption in As2S3: Self-trapped exciton recombination in amorphous chalcogenides

“…This is a well-known prototype material to understand the glass-forming tendency in chalcogenides [2]. Upon bandgap and near-bandgap illuminations, chalcogenide glasses exhibit numerous light induced effects in the form of photodarkening [3][4][5], anisotropy [6] and volume expansion [7]. These effects find immense potential applications in the field of optics and optoelectronics [8], hologram recording [9] and waveguide design [10].…”

Strong exciton-localized plasmon coupling in a-Ge24Se76/AuNP heterostructure

“…1(d) contain two vibrational modes, one from the corner sharing Ge-Se tetrahedra at 193 cm −1 and the other from Se-Se polymeric chain at 256 cm −1 . 20 Strikingly, there is a large enhancement of the intensity of Ge-Se and Se-Se Raman signals in the heterostructures, which can be attributed to the surface enhanced Raman scattering. 21,22 To study the coupling between the exciton and the localized surface plasmon, we have employed femtosecond (fs) time resolved pump-probe transient absorption (TA) spectroscopy (for details see Ref.…”