CHARACTERIZATION OF REFRACTIVE-INDEX CHANGE INDUCED BY ELECTRON-IRRADIATION IN AMORPHOUS THIN AS2S3 FILMS

Binary diffraction gratings in As2S3 films were prepared with the aid of an electron beam. The dose of the electrons was varied. The grating s were read with a HeNe laser, and the zero-order and first-order diff raction efficiencies were noted. Rigorous diffraction theory was used to give a homogeneous approximation for the refractive index change. R eactive ion etching was applied to reduce the thickness of the film, a nd a new value for the refractive index change was evaluated. The refr active index change versus film thickness dependence was found to be l inear at low electron doses and Gaussian shaped at higher doses. Throu gh a simple mathematical analysis, the absolute value of the refractiv e index was determined as a function of the position inside the film. At higher doses, the refractive index change was found to have a maxim um value of 3%, approximately 1.2 mu m from the film surface. (C) 1997 American Institute of Physics.