K and L X-ray thresholds in III-VI layer semiconductors

The absorption spectra at the Ga K-edges in GaS and GaSe, and the In L-edges in InSe have been measured as a function of the polarization with respect to the crystal c axis using synchrotron radiation. The transitions associated with the lowest energy structure in the Ga K spectra were found to be allowed only for ε ⊥ c, and were attributed to final Ga 4pxpy high-lying conduction bands. Transitions to the lowest pz-like conduction bands were not observed in both polarizations in the Ga K spectra, but they were in the In L spectra. These experimental results allowed us to identify the atomic character of the lowest conduction bands. In support of recent calculations, we found that the lowest conduction band states are formed by Ga 4s (In 5s) states and not by Ga 4pz (In 5pz) orbitals. The second group of conduction bands derive from chalcogen orbitals and the third group from Ga 4pxpy (In 5pxpy), and in part from empty s orbitals.