Photoemission study of GaAs_1−xP_x and Ga_1−xAl_xP mixed crystals

The different kinds of mixed crystal systems for GaAs_1–xP_x and Ga_1–xAl_xP have been investigated by x‐ray photoemission spectroscopy (XPS). The core level binding energies of Ga in GaAs_1−xP_x increase, whereas those of P in GaAs_1−xAlP_xP decrease with composition x, which are analyzed using Pauling’s ionicity and the ionicity scale of Kowalczyk et al. For two kinds of mixed crystals, we found that the energies of plasmon loss peaks increase, all major peaks in the valence band shift the band edge, and the top of the valence band recedes linearly with composition x. The composition variation of the energy gap for mixed crystals are caused basically by the top of the valence band receding.