Electronic structure of Cu2CdGeSe4 single crystal as determined from X-ray spectroscopy data

We report on studies of the electronic structure of Cu2CdGeSe4 single crystal by using X-ray photoelectron spectroscopy (XPS) and X-ray emission spectroscopy (XES). In particular, X-ray photoelectron core-level and valence-band spectra for pristine and Ar+ ion-irradiated surfaces of the Cu2CdGeSe4 single crystal have been recorded. Our XPS results indicate that Cu2CdGeSe4 is rather rigid with respect to Ar+ ion-irradiation: such a treatment does not induce any significant changes of values of the binding energies of core-level electrons as well as of the shapes of the XPS core-level and valence-band spectra of the Cu2CdGeSe4 surface. For the Cu2CdGeSe4 single crystal, the XES bands representing the energy distribution of mainly the valence Cu d, Cd d, Ge p and Se p states have been measured and compared on a common energy scale with its XPS valence-band spectrum. Such a comparison allows for concluding that the Cu 3d and Cd 4d states contribute mainly at the top and at the bottom of the valence band, respectively, while the Ge 4p and Se 4p states in the central and upper portions of the band. These experimental findings are found to be in agreement with literature data of band-structure calculations for this compound.