Photostructural change in the Urbach tail in chalcogenide glasses

Abstract

Absorption properties in the Urbach tail range were studied in relation to the photostructural change (PSC) or the photodarkening effect in amorphous-chalcogenide semiconductors. A reversible absorption change in the Urbach tail of amorphous-chalcogenide films due to photoirradiation and heat treatment is first reported. The Urbach tail is relaxed by photoirradiation and recovered by heat treatment, an effect which is associated with the effect of the photoenhanced far-infrared band broadening in amorphous-cha1cogenide films. Temperature dependence of the absorption is found to be closely associated with the frequency of the dominant far-infrared absorption of the vibration mode. It is indicated that optically excited randomness, due to the photostructural change, contributes to the photoenhanced relaxation of the exponential tail slope. Analysis of the tail slope parameter reveals strong electron-phonon couplings at the Ge-Se (S) or As-Se (S) bond. The photostructural change physical mechanism is discussed, and the frozen-in fictive temperature concept is found adequate.

Photoinduced dichroism and its low-temperature characteristics in obliquely deposited amorphous As–Ge–Se–S thin films

“…Especially, the exponential slope reduction has been reported due to the increase of randomness in atomic configuration. 21,22 As shown in Fig. 3, the absorption property of the film deposited at ϭ30°() are similar to that at 0°͑᭹͒.…”

Influence of the additive Ag for crystallization of amorphous Ge–Sb–Te thin films

“…Two slopes, B 1/2 and U offer information on the atomic and electronic configuration in the extended and Urbach regions, respectively. A slope reduction has been reported due to the increase of randomness in atomic configuration [17]. In particular, it could be thought that the reduction of U results from an increase of band-tail states in amorphous chalcogenide.…”

Linear Relationship between Photo-Induced Changes in Gap Energy and Refractive Index of Chalcogenide Glasses

“…This shows the n-values in the wavelength region of 0.6 to 1.0 mm and the Dn values at a = 2 Â 10 3 cm ± ±1 , which gives nearly corresponding gap energies for their low absorption [3]. In Table 1, we notice that the materials with large Dn/n values provide a large absorption edge shift ± ±DE go /E go .…”