Scientific Bulletin. Physical and Mathematical Research


In this paper, a theoretical method to study the spectral characteristics of the absorption coefficient, namely the area of ​​defective absorption of amorphous hydrogenated silicon according to the Davis-Mott approximation from the Kubo-Greenwood formula. It is shown that using the experimental spectral characteristic of the defect absorption coefficient, one can determine the energy position of defects in the mobility gap. Optical transitions of electrons, in which electronic states participate in defects, indicate that there are three types of optical transitions of electrons: between defects, between defects and tails of allowed zones, and also between defects and allowed zones. It was found that the absorption coefficient determined by the optical transitions between defects and allowed zones play a major role in them. The spectra of the optical absorption coefficient for the region of the defect absorption coefficient are obtained. To obtain the analytical views of these spectra, the density distribution of electronic states located in defects is chosen in the form: Gaussian distribution or hyperbolic secant distribution. The density of electronic states within the boundaries of the allowed bands obeyed the parabolic, linear, and Gaussian distribution. It is shown that the values and the form of the spectra of the defect absorption coefficient are determined by the electron density distribution in the allowed bands. It is shown that the analytical expressions of the spectra can be calculated with two different methods and the resulting expressions differ from each other, but their graphs define the same curve. The electron density distribution within the allowed bands is power-law, the defect absorption spectra had a weak maximum when the energy of the absorbed photons is на ħω = εC-εD and ħω = εD-εV. It was also shown that the maxima appear in the spectra of the defect absorption coefficient only when the pronounced maxima in the density distribution of electronic states at the boundaries of the valence band or conduction band. It is determined that these maxima are in the energy position ħω = εC-εD or ħω = εD-εV. At the same time, irrespective of the charge state of defects, such as neutral, positive or negative, they participate simultaneously in the optical transitions between the valence band and the defect, as well as between the defect and the conduction band. The results obtained in this article can also be applied to dopants. It is shown that the formula used to determine the defect concentration of amorphous hydrogenated silicon in [8] cannot be used by all amorphous semiconductors. It is also shown that the incompatibility of the results presented in [9] and [10] can be eliminated by the results obtained in this paper. Thus, in the present work it is shown that the experimental defect absorption spectra can be applied to detect the energy position of defects of amorphous hydrogenated silicon. As it is known, the main defects of amorphous hydrogenated silicon are found, D0 is neutral, D- is negative and D+ is positive charge states, energy positions are located in the intervals εC-εD0 = 0,95-1,05 eV, εC-εD- = 0,65-0,75 eV, εC-εD+ = 0,35-0,45 eV. Given this, from the experimental results obtained for the defective absorption of amorphous hydrogenated silicon in the present work, it can be assumed that the main defect of amorphous hydrogenated silicon is the neutral defect D0, and its energy position is within εC-εD- = 0,65-0,75 eV.

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