Temperature dependence of the optical properties of manganese-doped Cu2GeSe3

The optical absorption on synthesized Mn-doped Cu2GeSe3 samples was made to determine the variation of the energy gap E-g as a function of temperature in the range 9 to 300 K at photon energies hv = 0.81 to 0.50 eV. The data are analyzed by considering the Manoogian-Woolley equation and using the Va rshni relation for the temperature dependence of semiconductor band gaps. T he formula is shown to be compatible with the assumption about the influenc e of phonons on the band gap energy. Above about 100 K the temperature coef ficient of the fundamental edge is dE(g)/dT = -1.5 x 10(-4) eV K. The estim ated value of the Debye temperature is in agreement with theta(D) = 170 K r eported from specific heat measurements. Additionally, a band gap shift due to the incorporation of manganese in the crystal lattice was observed. The results are discussed in regard to some general trends found in the I-2-IV -VI3 compounds.