Infrared and X-ray photoelectron spectroscopic study of photostructural changes in amorphous P-Ge-Se thin films

The structure of thin films of P40-xGexSe60 glasses deposited at various angles of incidence and the photostructural changes occurring therein on illumination with UV light have been studied by far-infrared (IR) spectroscopy and X-ray photoelectron spectroscopy (XPS). IR spectra reveal the absorption bands due to P=Se, P-Se-P, Ge-Se, and -Se-Se- group vibrations. The coexistence of various types of structural units (SePSe3/2, PSe3/2, GeSe4/2, -Se-Se-) in these films is supported by XPS and IR results. The photostructural changes are a consequence of the changes in the relative concentration of these structural units. Annealing of the films also causes a change in the concentration of these structural units, which in turn gives rise to a partial reversibility of the photoeffects. It has been established that the magnitude of the photostructural changes is maximum for the composition (P20Ge20Se60) having maximum concentration of fourfold coordinated units