Structural disorder in CDSxSe1-x thin film probed by microdiffraction and optical spectroscopies

X-ray diffraction with a large area detector from CdSxSe1-x alloy thin films, deposited on Si (111)-oriented substrates by laser ablation technique, allowed us to point out the effects of structural disorder which can not be observed by conventional -2 diffractometers. The X-ray spectra measured by using conventional -2 diffractometer have shown that the CdSxSe1-x films grow oriented along the (002)-direction in the hexagonal phase with the c-axis perpendicular to the film layers. The width of the 002 reflection is probably related to substitutional disorder arisng from alloying. However, further disorder effects are detected when one resorts to microdiffraction. Indeed, the broadening along the Debye rings reveals that the films are not perfectly epitaxially grown. Moreover, only two families of planes are present in the microdiffraction spectra of all samples. This finding is discussed by considering a structural disorder not related to alloying. An attempt to simulate this structural disorder has been carried out on the basis of symmetry considerations and discussed. A correlation is found with the results of luminescence and Raman spectroscopies that give evidence of disorder effects in terms of excitation localization in photoluminescence and a broad, disorder activated, band in the Raman spectra.