Multielectron Excitations in Photoemission Spectra of Chalcogenide Semiconductors

Two types of multielectron effects of X-ray photoemission in chalcogenide semiconductors Cu₂SnS₃, Cu(In,Ga)Se₂, and CuGaTe₂ have been experimentally studied. The first type is interatomic Auger transitions with electron ejection from the inner levels of atoms surrounding copper (Sn, In, Ga), which arise as a result of the decay of the photohole formed on copper atoms during absorption of synchrotron radiation. And the second type is the characteristic loss of kinetic energy during direct photoemission from the core–electron levels of tin atoms due to the dynamic Coulomb field of the photohole, the inclusion of which leads to the shaking of Sn4d electrons into unoccupied states. The cause of both effects is the extremely nonequilibrium nature of the atom photoionization, which generates an almost instantaneous inclusion of the Coulomb field of the photohole in one of the inner levels of the atom. The surrounding electrons are subjected to a kind of impact and can increase their energy by tens of electron volts. The experiments show that the electrons of the 4d levels are “shaken up” most effectively. Firstly, there are many of them (ten per atom) and, secondly, due to the large centrifugal barrier, these electrons are on the periphery of the atom, as are unoccupied free states, into which they pass when the photohole field is turned on.