Thin Solid Films, 164 (1988) 51-56 51 STUDY OF MICROSTRUCTURE OF AMORPHOUS Ge-Se FILMS USING SPECTROSCOPIC ELLIPSOMETRY* SATYENDRA KUMARt, D. K. PANDYA AND K. L. CHOPRA~ Thin Film Laboratory, Physics Department, Indian Institute of Technology, Hauz Khas, New Delhi 110016 (India) The dielectric function spectra ~ =/31 --ig 2 of evaporated amorphous Ge-Se films in the energy range 2-5.2 eV have been studied using spectroscopic ellipsom- etry (SE). The ~ spectra of GexSel_~ (0.2~<x~<0.33) films exhibit a two-peak behaviour showing the presence of a well-separated lone-pair band on top of the valence band. The effect of composition, angle of deposition and photoexposure have been studied. Detailed analyses of SE data have been carried out to yield quantitative information on the microstructure of the films. I. INTRODUCTION Amorphous chalcogenides, in contrast to amorphous silicon and germanium, with their lower coordination and highly polarizable lone-pair (LP) orbitals exhibit electronic and structural flexibility which is responsible for many observed phenomena such as the photostructural changes peculiar to this class of materials. Our laboratory has reported I a number of interesting phenomena when these films are exposed to band gap photons, energetic electrons and ions. In particular, photoexposure of amorphous chalcogenide films leads to changes in the optical constants and a shift in the optical absorption edge 2. The studies 1 of optical constants in the vicinity of the absorption edge have yielded significant information on the role of various atoms in the chalcogenide network. A direct determination of the dielectric function in the interband transition region is expected to provide information on the electronic band structure and microstructural aspects of virgin and irradiated chalcogenide films. Ellipsometry being sensitive to the surfaces can detect small changes in composition and microstructure at the film surface. Spectroscopic ellipsometry (SE) has earlier 3 been employed to study the optical spectra of crystalline and glassy GeSe2 films. In this paper, we report the results of a detailed SE study on the optical properties and microstructure of amorphous GexSel_ x films as a function of composition, angle of deposition and photoexposure. * Paper presented at the 7th International Conferenceon Thin Films, New Delhi, India, December7 11, 1987. t Present address: Laboratoire de Physique des Interfaces et des Couches Minces, Ecole Polytechnique, 91128 Palaiseau C6dex, France. :~ Present address: Indian Institute of Technology, Kharagpur 721302, India. 0040-6090/88/$3.50 © ElsevierSequoia/Printed in The Netherlands