Optical properties and structure of As-Ge-Se thin films

Abstract

Abstract. Thin chalcogenide films with compositions As 10 Ge 22.5 Se 67.5 and As 12 Ge 33 Se 55 have been investigated. Optical constants and thicknesses of these films were obtained from transmission spectra. Structure of initial bulk glasses and films were investigated by Raman spectroscopy. Both films are estimated to have high values of the nonlinear refractive index. Keywords: chalcogenide films, optical properties, nonlinearity, Raman spectra. Manuscript received 12.02.10; accepted for publication 08.07.10; published online 30.09.10. 1. Introduction © 2010, V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine ()Chalcogenide glassy semiconductors (ChGS) are attracting attention of many researches since the discovery of their semiconductor properties in the 1950s. This is due to their unique properties such as transparency in infrared region of spectrum, high stability and a number of photoinduced phenomena (photodarkening, photobleaching, photocrystallization, etc.). Recently, high attention has been paid to the nonlinear optical properties of ChGS. Measurements of nonlinear refractive index have shown that its value can range from 100 to 1000 times of that in silica glass. High nonlinear refractive index combined with moderate to low nonlinear absorption can be exploited in all optical signal processing devices to enhance performances of telecommunication systems. ChGS are very suitable for these kinds of applications, because they are compatible with well established silica-on-silicon and fiber drawing technologies. The nature of glassy state provides an opportunity to adjust the composition and therefore, to tune smoothly the properties of material. Photoinduced phenomena allow the local modification of the material properties by the exposure to suitable radiation which can be utilized in writing waveguide channels, diffraction gratings and so forth. Quite complicated experimental techniques are exploited for determination of nonlinear refractive index. To avoid these difficulties several semiempirical relations have been proposed in literature to estimate the nonlinear refractive index or third order nonlinear susceptibility from other known parameters such as the linear refractive index, first order susceptibility, bandgap energy, etc. The most simple of these relations is based on using the generalized Miller’s rule [1]. According to this rule, third order nonlinear susceptibility can be estimated as