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The region of fundamental absorption in the optical spectra of amorphous semiconductors is theoretically studied using the Davis-Mott approximation according to the Kubo-Greenwood formula. As is known, three types of optical transitions of the electron can be observed in the fundamental absorption region; from the tail of the valence band to the conduction band, from the valence band to the conduction band and from the valence band to the tail of the conduction band. For all these electronic transitions, analytical expressions of the partial absorption spectra are obtained from two different types of the Kubo-Greenwood formula. The width of the optical mobility gap and the proportionality coefficient were determined in the analytical form of the interband absorption spectrum by fitting them to the experimental interband absorption spectrum. A new method is presented for calculating the density of distribution of electronic states in the conduction band of amorphous carbon based on the experimental interband absorption spectrum and the analytical expression of the Kubo-Greenwood formula written for the interband absorption spectrum.

In this work, defect absorption spectra for defects characteristic of hydrogenated amorphous silicon are theoretically studied. It is shown that in order to determine defect absorption spectra using the Kubo-Greenwood formula, the indefinite integral in this formula must be written in a certain form. It was discovered that electronic transitions involving defect states are divided into two parts depending on the energy of absorbed photons. The values of the partial defect absorption spectrum at low energies of absorbed photons have almost no effect on the overall defect absorption spectrum. It has been established that the main role in determining the defect absorption spectrum is played by partial spectra determined by optical transitions of electrons between allowed bands and defects. It is shown that with a power-law distribution of the density of electronic states in allowed bands, the spectra of optical transitions between them and defects do not depend on the value of this power.