ON THE STRUCTURAL STABILITY OF AMORPHOUS SE CDSE MULTILAYERS - A RAMAN-STUDY/

The effects of thermal annealing and laser beam illumination on the st ructure of amorphous Se/CdSe multilayers of up to 20 periods and vario us sublayer thicknesses (3.5, 5, 6.5 and 10 nm) have been studied by m easuring the higher frequency (vibrational) Raman spectra. Three Raman bands have been observed in this spectral region at 209 cm(-1) (CdSe) , 237 cm(-1) (Se) and 256 cm(-1) (Se). After annealing, the intensity of these bands increases for all amorphous multilayers (AML) samples w hich, in a fil st approach, indicates an improvement of interface qual ity. In AML of thin (< 5 nm) sublayers, annealing results in an increa sed ordering of both Se and CdSe sublayers, while in AML of thicker (> 5 nm) sublayers the opposite effect is concluded for Sr sublayers, an d hardly any change for CdSe ones. A gradual increase of laser power d ensity causes a likewise modification of Raman spectra, which is attri buted to crystallization of Se sublayers; in similar low temperature ( 25 K) experiments (using even higher laser power densities) there is n o indication of substantial crystallization, implying that the latter is mainly a thermal effect. From the threshold for crystallization, we observed that the structural stability of Se/CdSe AML is better, the smaller the sublayer thickness, an important result for electrophotogr aphic applications. (C) 1998 Elsevier Science B.V.