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Lattice-dynamical aspects are coherently applied to the reversible photostructural change (PSC) effect and associated phenomena in chalcogenide glasses. Far-infrared, X-ray photoelectron and optical absorption measurements reveal that photo-induced distortions and quenching in lattice configurations are characterized by increased randomness, which can be reversed by thermal annealing for full recovery. A statistical analysis reveals clearly that PSCs such as photodarkening and photoexpansion are essentially equivalent to a thermally frozen-in effect. The PSCs can be directly traced to the strong electron-lattice coupling and localized bond strain of chalcogenide glasses. A lattice-dynamic energy diagram highlights the importance of the quadratic-term of atomic distortion (δq)2 in relating PSC to the glass transition phenomenon. The photochemical and photodoping effects are then described, on the same basis, in terms of the lattice fluctuation and high fictive temperature.

A Ag-Se/Ge-Se inorganic resist is applied in x-ray lithography using synchrotron radiation (SR). Usable sensitivity of 0.3–3 times that of a polymethylmethacrylate (PMMA) resist and high contrast (γ∼3.5) are obtained through SR exposures. By utilizing the fringes of masked SR flux caused by Fresnel diffraction, 500-Å-wide fine lines are formed by using x rays of 2–10 Å in wavelength. It is determined that a high-density resist, such as a Ag-Se/Ge-Se inorganic resist, is favorable for forming micropatterns using x rays because of the short ranges of the electrons generated by the x rays in the resist.

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.

In As-Se- (S) -Ge amorphous films, a remarkable difference of chemical etching rate between the heat-treated state and the light-irradiated state has been observed. Utilizing this characteristic, a relief-type diffraction grating of the amorphous film was obtained (the pitch between grating lines, 0.86 μm). This grating has achieved a high diffraction efficiency of 15.8%, which was about 10 times greater than before chemical etching.