Fundamental optical absorption edge in MnGa2Te4 single crystals

Abstract

A study is made of the optical properties of oriented MnGa2Te4 crystals in the region of the fundamental absorption edge. The energy gap width for the temperatures 77, 300, and 370 K is determined to be EG = 1.635, 1.52, and 1.50 eV. The spectral response α(hω) is found to follow Urbach's rule throughout the temperature range studied, the slope of the absorption edge remaining constant (α > 102 cm−1). Crystal annealing with subsequent rapid cooling results in a shift of the absorption edge longward by 25 meV with the exponential form of α(hω) prevailing over the range T = 77 to 370 K. An analysis shows the optical absorption in the region of the fundamental edge to be a sum of the effects coming from the density-of-states tails, local scattering centers associated with a high vacancy concentration, and electron–phonon interaction. Optical linear dichroism of the absorption edge of MnGa2Te4 single crystals with pseudotetragonal structure is revealed and studied. The single crystals are established to be optically uniaxial, their optical transmission dichroism being negative. It is shown that the minimal direct optical transitions in MnGa2Te4 are allowed in the E ∥ c polarization in the temperature range 77 to 370 K, the crystal-field splitting of the valence band increasing with temperature. [Russian Text Ignored].