| Abstrakt: |
Ternary semiconductor materials with a chalcopyrite structure belonging to the I-III-VI2 group (where I = Ag, Cu; III = Al, Ga, In; VI = S, Se, Te) attract considerable attention due to interesting physical properties. The structural, electronic and optical properties of these crystals make them promising materials for a number of applications in nonlinear optics devices, detectors, photodiodes, solar cells, etc. In this work, the theoretical first-principle calculations of the structural, vibrational and dielectric properties of an AgGaS2 crystal with a chalcopyrite structure are performed. We report the results of the calculations of the phonon band structure w(q), total and partial density of phonon states N(w), infrared spectra and Raman spectra, the Born effective charge tensor for each atom, and dielectric constants (for w = 0 and → 0) using the theory of perturbation of the density functional. Theoretical-group analysis of vibrational modes is carried out and the classiffication of vibrations in the phonon spectra of the investigated compound is performed. The results of the phonons calculations showed the stability of the crystal structure of the studied compound. It follows from the calculations of the phonon spectrum that there is a significant anisotropy of low-frequency acoustic branches of vibrations. There is also a presence of low-frequency optical branches that interact with acoustic ones. It was found that the density of states can be divided into three parts - low-frequency, medium-frequency and high-frequency regions, which are formed by the oscillations of Ag, Ga and S atoms, respectively. The calculated and identified frequencies of vibrations modes in the center of the Brillouin zone (... point) showed good agreement with the available experimental data on IR and Raman spectra and theoretical data obtained using the Phonon program. A symmetric classification of vibrational modes for a crystal using group theory is performed. Estimation of the Born effective charge tensor and dielectric constants in an AgGaS2 crystal indicates their significant anisotropy. [ABSTRACT FROM AUTHOR] |
