6533b822fe1ef96bd127d50b

RESEARCH PRODUCT

<title>Holographic recording in amorphous chalcogenide semiconductor thin films</title>

subject

description

ABSTRACT The photoinduced changes ofoptical properties and holographic recording in amorphous chalcogenide semiconductor As-S- Se and As2S3 thin films have been studied. The possibilities of the practical applications of these materials as the photoresists for the production of the relief holograms and holographic optical elements are discussed. It is shown that theself-enhancement phenomenon of holographic recording in amorphous chalcogenide semiconductor films by light orthermal treatment can be used to increase the diffraction efficiency ofthe holograms.Keywords: chalcogenide semiconductors, amorphous films, photoresists, photoinduced processes, relaxation processes,self-enhancement of holograms 1. INTRODUCTION Amorphous chalcogenide semiconductor (AChS) films exhibit a number of remarkable photo-induced (Phi) structural changes leading to phenomena such as photo-darkening1 (a red shift of the absorption edge) and photo-refraction2 (refractive index change), changes in hardness and density, changes in chemical properties" as well as optical anisotropies5such as dichroism, birefringence and gyroscopy. The photodarkening and photoinduced refractive-index changes are themost frequently studied phenomena due to their applicability for practical purposes. The refractive index increase by i.n0.6 at the photon energy of 1.96 eV has been observed in amorphous As-Se films by laser exposure3. Depending on thepreparation conditions, the photoinduced changes in the AChS can be either reversible or irreversible. Irreversible changesare usually observed in amorphous thin films prepared by the vacuum thermal deposition or the sputtering process, whilethe well-annealed films possess the reversible photoinduced changes produced by repeated cycles of band-gap illuminationand annealing near the glass transition temperature Tg.The phenomenon of the photo- and the electron-beam induced changes in dissolution rate of the large group of the AChSfilms was the basis for extensive development of a new class of inorganic resists8. Amorphous As-S, As-Se and As-S-Sefilms have been used recently as promising materials for photolithography in visible spectrum (?65O nm) with highresolution (>5000 lines/mm) and satisfactory light sensitivity (lO' J/cm2). The AChS photoresists are successfully appliedin the manufacturing process of embossed rainbow holographic labels by Hologramma Ltd in Riga. The AChS resistsobtained by the thermal deposition method in vacuum are characterized by a very high resolution capability and they have anumber ofpeculiarities that make them attractive for application in many photo- and electron-beam lithographic processes.During the studies ofthe holographic properties of amorphous As-S films doped with bromide an increase ofthe diffractionefficiency (DE) after the recording was observed by Brandes et al.9. This phenomenon called relaxation (or dark) self-