Manifestation of electric dipole selection rules in angle resolved photoemission spectra from zinc blende semiconductors

We use angle resolved photoemission spectroscopy to determine critical point energies of the Γ7, Γ8, and X6 levels and the valence band dispersion E(k) along the [100] direction of Cd0.8Zn0.2Te. The experimental analysis is carried out without assuming any specific form of the final state bands. Normal emission valence band spectra provide clear evidence of a band gap opening in the final state bands. The crystal potential, which perturbs the final states, causes the conduction band Γ point at ∼12.5 eV to split by ≥0.60 eV. In addition to this very pronounced band gap, we find smaller gaps in the final states at k vectors ∼1/3 and 2/3 towards the X point. Relying on structural arguments, we also deduce the symmetries of the final state bands.