Laser induced changes of the optical properties of obliquely deposited thin chalcogenide films A. Lalova * , R. Todorov Institute of Optical Materials and Technologies “Acad. J. Malinowski”, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., bl. 109, 1113 Sofia, Bulgaria. ABSTRACT The object of the present work is investigation of the role of the actual conditions of illumination on the magnitude of photo-darkening for a specific material (the incident photon flux and the penetration depth of absorbed photons). It was found that the photo-induced changes in the thin As 2 S 3 film depend on the light intensity and they are affected by heating of the material at higher laser intensities. The influence of the deposition rate on the film’s microstructure was investigated. The conditions for deposition of coatings with columnar structure were determined. The photo-induced changes of the optical properties of the obliquely deposited thin As 40-x Ge x S 60 films are examined. It was established that the microstructure of thin As-Ge-S films can a play significant role in photo-induced volume changes. Keyword list: Chalcogenide glass, Thin films, Oblique deposition, Optical properties, Photo-induced changes 1. INTRODUCTION The microstructure of amorphous thin films is strongly dependent on the temperature, rate of evaporation and angle of deposition 1 . The segmental layers structures and in particular the columnar structure can play significant role in the photo-induced changes producing during the light illumination deformations from interlayer-type 2 . The photo-induced changes of obliquely deposited thin chalcogenide films with compositions Se, GeSe 3 , As 2 S 3 , PbAs 2 S 4 have been investigated in Ref. 2 and 3. Rajagopalan et al. 3 have observed increasing of the photo-induced changes with increasing of the deposition angle for arsenic containing thin film. They found an effect of photobleaching for thin GeSe 3 film at normal incidence and photodarkening for obliqueness greater than 40˚. The authors of the same work reported columnar microstructure for all films deposited at angles greater than 40˚. Considerable attention has been paid to the photoinduced phenomena of thin amorphous films from Ge-As-S system 4-9 . Thermal and photo-induced bleaching was observed in the virgin Ge-As-S films while reversible photo-darkening is occurred in annealed coatings 9 . Еffect of ‘giant’ volume expansion in thin Ge 27 As 13 S 60 was reported 5 which makes thin chalcogenide films perspective materials for fabrication of microlens. The present work is focused on the influence of the conditions of illumination and microstructure of obliquely deposited thin films from As-Ge-S system on the photo-induced changes of the optical properties. 2. EXPERIMENTAL DETAILS Bulk glasses from the system As - S - Ge were synthesized in a quartz ampoule from elements of 99,999 % purity by the method of melt quenching 7 . Thin films from previously synthesized bulk glasses from As 40-x Ge x S 60 system (for x = 0, 10, 30) were deposited by thermal evaporation on rotating substrates or by well-known oblique deposition technique at angle of deposition 75˚.The bulk materials were evaporated from a Ta boat (“Knudsen type”). The deposition rate was varied in the range of 0.05 - 1 nm/s. In the case of substrates continuously rotated during the evaporation process the substrate * E-mail: annielalova@gmail.com, Tel.: +395 2 9793521, Fax.: +359 2 8720073, http://www.iomt.bas.bg/ 17th International School on Quantum Electronics: Laser Physics and Applications, edited by Tanja Dreischuh, Albena Daskalova, Proc. of SPIE Vol. 8770, 87700A © 2013 SPIE · CCC code: 0277-786X/13/$18 · doi: 10.1117/12.2013735 Proc. of SPIE Vol. 8770 87700A-1 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 03/25/2013 Terms of Use: http://spiedl.org/terms