X-Ray Photoelectron Study of the Valence Bands in Cuprous Halides

The x-ray photoelectron spectra of the valence bands of CuCl, CuBr, and CuI have been measured. The spectra show that the valence bands of these materials consist of two branches. The existence of a forbidden band between the two branches and a few additional structures are revealed by the deconvolution of the spectra with a measured instrumental response function. The average $p \ensuremath{-}d$ mixing rates in the valence bands are evaluated by taking the transition matrix elements into account. It is shown that the upper branch of the valence bands arises mostly from the $3d$ states of a cuprous ion, in accordance with the optical-absorption spectra in the ultraviolet region. The results are compared with other experimental and theoretical data. Especially, the fundamental absorption spectra are reinterpreted.