Core Absorption Spectra of Crystalline and Amorphous GeTe Thin Films

Core absorption spectra of crystalline ( c -) and amorphous ( a -) GeTe thin films have been measured in the 26-70 eV region. Photoemission spectra have also been measured to determine the binding energies of Ge 3 d and Te 4 d core levels. In the c -phase Ge 3 d absorption shows excitonic peaks which can be explained in atomic picture, while Te 4 d absorption shows broad structures which reflect DOS of the conduction band. A small peak was found below the broad structures of Te 4 d absorption, the origin of which is the excitonic transition or the transition to the hole states generated by Ge vacancies located near the top of the valence band. In the a -phase Ge 3 d absorption shows a broad structure while Te 4 d absorption somewhat sharp doublet. The difference in the spectral features in both phases suggests that the bonding character is more covalent in a -GeTe than in c -GeTe.