Structural correlations in light irradiated Ge 36Se 64 amorphous films—Radial distribution function study

Abstract

The effect of laser irradiation on the electronic structure of amorphous Ge 36Se 64 films has been detected by studying the variation of the bond length ( r) and the coordination number C N. The total distribution function T( r) of the as deposited film is characterized by the first coordination sphere corresponding to the superposition of the correlation Ge–Se and Se–Se situated at 2.53 Å. The average estimated C N is 2.519. The second peak ascribed to the correlation Se–Se lies at 3.85 Å showing good agreement with other published data. After irradiation, the first peak of T( r) shows a considerable shift towards a small r and a reduction of C N. On the contrary, the second neighbor data shows a slight increase of r and a great increment of C N value (5.11 before irradiation against 6.59 after irradiation). Study of the variation of both r and C N values induced by subsequent annealing of the film is also given. The relative concentrations of the Ge Ge, Ge Se and Se Se bonds, as well as, the number of the GeSe 4 tetrahedral per atom are calculated using the continuous random network (CRN) and the chemically order continuous random network (COCRN) models. These calculations argue the presence of Ge 2(Se 1/2) 6 ethane like unit in addition to Ge(Se 4) 1/2 even with the COCRN model. The formation of dynamical bonds during irradiation of the film under study is suggested. Correlation to volume changes during illumination studied by tight binding molecular dynamics computer simulation has been also considered.