Valence bands of amorphous and crystalline GeTe determined by X‐ray and UV photoemission

The density of valence states, the energies of the core levels, and the characteristic energy loss spectra of crystalline and amorphous GeTe have been measured by X‐ray (1486.6 eV) and UV (21.2 eV) photoemission spectroscopy. The valence band densities of states of the two GeTe phases are in general similar, but exhibit distinct differences in their detailed structure. That of the amorphous form of GeTe may be approximated by a sum of the densities of states of the elemental forms of amorphous Ge and Te. A model for the valence band density of states is proposed which may be generally applicable to random covalent networks. No difference in the separation of the core level of the Ge and Te atoms is found between the amorphous and crystalline phases, thus indicating that there is no significant ionicity difference in the bonding character of these two phases. In light of the current structural models for the amorphous form, the similarities between the photoemission from the two phases are surprising. The plasma frequencies of the amorphous and crystalline forms are found to be 16.4 and 16.9 eV, respectively.