Investigation Of The Preparation And The Photo-induced Structural Changes In Ge-Sb-Se Thin Films

Light-induced structural changes are the most interesting phenomena in amorphous chalcogenides.The bond configurations of Ge-Sb-Se chalcogenide thin films can break and reform by light exposure,which produces some types of photo-induced changes in structure and properties.This system also exhibit attractive optical properties for optical devices,such as the broad infrared transparency,low optical losses,fast response time,high refractive index and relatively stable structure.Thus,Ge-Sb-Se thin films present a cornucopia of potential applications in the integrated optoelectronics field,like non-linear optics,xerography and holographic storage.In this thesis,we investigated the Ge-Se and Ge-Sb-Se films,studying the change of the transmittance and the phenomenon of photodarkening and photobleaching under the near-bandgap light irradiation.The kinetic parameters of Ge-Sb-Se thin films were obtained by using the kinetic fitting formula.The relationship between photo-induced phenomena and the mean coordination number was investigated.Raman spectroscopy was used to study the effect of this structural change.The main research results are as follows:?1?The thin films doped with Sb elements in the GeSe₂ and GeSe₄ depositing by radio-frequency magnetron sputtering have good amorphous properties and transmittance,but we found the transmission spectra of Ge-Sb-Se films have a red shift at the short wavelength absorption edge,and the transmittance decreased with increasing Sb content.?2?The thin films prepared by GeSe₂ and Sb targets have two kinds of opposite phenomena,the rapid photodarkening and slow photobleaching,which saturated to a certain state under 655 nm pump laser irradiation.In the thin films,which compositions ranging from Se-poor to Se-rich,the photo-induced changes of the films transformed from photodarkening to photobleaching.There is an intermediate stable state between two changes,and the mean coordination number in this state is about 2.69,which is close to the rigidity transition from 2-D to 3-D at a mean coordination number of 2.67.?3?The thin films prepared by GeSe₄ and Sb targets also have two opposite phenomena of photodarkening and photobleaching under 655 nm pump laser irradiation,but all of the films are photodarkning films.With the decreasing of Gecontent,the photobleaching phenomenon decreased until it disappeared completely.?4?GeSe₂ and GeSe₄ are both photobleaching films,but there is no photodarkening phenomenon in GeSe₂ thin films,and the photobleaching degree is higher than that of GeSe₄ films,which contains more germanium.?5?Through the analysis of Raman spectra,we can find that the photodarkening of the films is mainly due to the increasing of Ge-Geand Sb-Se bonds and the decreasing of Ge-Se bonds.The photobleaching is mainly because of the Ge-Se bond in corner-sharing GeSe₄ tetrahedral turned into the Ge-Se bond in edge-sharing GeSe₄ tetrahedron,and the decreasing of Ge-Geand Sb-Sb homopolar bonds.