For the first time, a reverse method of studying the spectral distribution curves of the photocurrent was applied, which allows to separate the contribution of equilibrium and non-equilibrium carriers.
 This publication is a continuation of the reviews [1-3]. In order to preserve the generality of the work, the numbering of sections is selected to be general. Numbers of formulas and figures are presented in sections. References to literature in each review are given individually.
 Cadmium sulfide crystals are used in our research as a convenient model material. The results obtained on them and the constructed models are also applied to other semiconductor substances.