OPTICAL PROPERTIES OF Dy-DOPED AgGaGe3Se8 CRYSTALLITES

Abstract

This study analyzes the impact of doping AgGaGe3Se8 crystals with Dy atoms on their optical properties. Phase control and chemical composition determination were conducted on the studied crystals. It was established that the crystal exhibits a single-phase morphology, although all samples show visible dark spots, lighter, and darker areas caused by the nonuniform surface roughness resulting from cutting and grinding. The content of the components is in good agreement with the initial composition of the synthesized sample, confirming the qualitative assessment of the elemental composition and homogeneity of the samples within the selected scanning area. To estimate the bandgap width, the spectral distribution of the absorption coefficient in the fundamental absorption edge region was investigated. It was found that the studied crystal is an indirect-gap semiconductor. The estimated bandgap width in the temperature range of 100-300 K is 2.23 eV at T=300 K and 2.41 eV at T=100 K. It was determined that the introduction of the rare-earth element (Dy) into AgGaGe3Se8 contributes to the increase in the bandgap width. It was established that the operating range of the studied crystal can be considered as the range from 0.6 μm to 15-16 μm. The temperature coefficient of the bandgap width change was determined to be -9*10-4 eV/K, which correlates with the value for AgGaGe3Se8 (-8.5*10-4 eV/K). The obtained results allow us to conclude about a single mechanism of thermal change in the bandgap width for all studied samples, since the coefficients describing this change have the same order. The Urbach parameters and the electron-phonon interaction constant were calculated. An analysis of the obtained data indicates an increase in the Urbach energy with increasing temperature of the samples in the range from 100 to 300 K, which can be explained by an increase in the concentration of charged defects, which at low temperatures were neutral but undergo thermal ionization when heated. It was established that doping leads to an increase in the electronphonon interaction constant. Such an increase is probably due to the presence of dysprosium (Dy) ions at the silver (Ag) sites and an increase in the concentration of vacancies in the silver sublattice. Both of these factors, as charged impurities, affect the electron-phonon interaction, enhancing it.