Effects of surface adhesion of nonequilibrium charge carriers in the photoconductivity spectra of CdS crystals

The relaxation of low-temperature ($T$ = 77 K) edge photoconductivity (PC) spectra of CdS crystals of the first group1 caused by the removal of the transverse electric field is investigated. A clearly manifested inversion of the fine (exciton) structure is found in the spectra during their relaxation to the initial form (existing before the application of the field). It is shown that the observed relaxation changes in the PC spectra of CdS are due to relaxation of the nonequilibrium surface charge appearing as a result of trapping of a part of the charge, induced by the transverse field into the sample, by slow surface states (adhesion levels). The experimental data on the effect of preliminary illumination by self-radiation on the edge PC spectra of the first-group CdS crystals indicating the existence of surface adhesion levels with a high density in these crystals are presented.