Optical Properties and Structure of Electroluminescent SiOx:Tb Films

Using nondestructive optical methods (measurement of transmission spectra in the visible and IR regions and multiangular ellipsometry), we have studied the structural changes in SiO _x :Tb films subjected to high–temperature annealing in air, which are responsible for the appearance of electroluminescence in light–emitting structures based on them. It has been established that the appearance of green electroluminescence in such a film (upon annealing of the film in air at temperatures of 600–800°C) is due to the structural changes in its matrix, leading to partial disproportionation of the thermally deposited SiO _x :Tb film (as a result, the film represents a mixture of several phases – Si, SiO_x, and SiO₂). Films showing blue electroluminescence (annealing temperature 1000°C) are characterized by a higher content of oxygen, a better compactness, and a better macroscopic homogeneity in comparison with films showing green electroluminescence. It is also shown that the thermal cycling accompanying the annealing leads to the appearance of birefringence and scattering in SiO _x O:Tb films. It is anticipated that the annealing–stimulated structural changes taking place at both the micro– and the macrolevel should cause changes in the local surroundings of the luminescence center and in the conditions for heating the charge carriers exciting the luminescence centers.