OPTICAL PROPERTIES OF PHASE-CHANGE CHALCOGENIDES IN THE IR RANGE

Background. The work is devoted to the study of the optical properties of chalcogenide compounds (GeTe) x (Sb 2 Te 3 ) 1 - x , which are promising for use as functional materials in non-volatile memory devices and displays. Information storage is based on the contrast of physical properties between the crystalline and amorphous states of these compounds, which in a metastable crystalline state form a distorted cubic lattice with a high concentration of vacancies. Objective. The aim of the paper is to study the influence of structural and thermally induced disorder on the contribution of free charge carriers to the dielectric function of (GeTe) x (Sb 2 Te 3 ) 1 - x chalcogenides and on the optical properties of these materials in the vicinity of the main edge of optical absorption. Methods. The results were obtained by analysis of IR reflectance spectra of the (GeTe) x (Sb 2 Te 3 ) 1 - x samples. Results. It was determined that the width of localized electronic states, the Tauc parameter, and the contribution of plasmons to the dielectric function of phase change chalcogenides (GeTe) x (Sb 2 Te 3 ) 1 - x depend on the concentration of vacancies and their ordering. The data obtained confirm that a change in the concentration of vacancies and their ordering in samples of (GeTe) x (Sb 2 Te 3 ) 1 - x chalcogenides leads to change of the type of their electroconductivity. Conclusions. The width of the localized electronic states and Tauc parameter depend on the concentration of vacancies and their ordering. A decrease in the concentration of vacancies leads to an increase in the contribution of free charge carriers to the dielectric function of (GeTe) x (Sb 2 Te 3 ) 1 - x ; their ordering entails large changes in the values of the plasmon frequency and their damping coefficient. The results provide information on ways of (GeTe) x (Sb 2 Te 3 ) 1 - x properties’ modification.