The effect of Tl addition on the electrical and thermal transport properties of amorphous As2Se3

The effect of Tl addition on the electrical and thermal properties of the binary chalcogenide semiconductor As2Se3 has been studied in the homogeneous glass-forming region. The thallium in the ternary system (As2Se3)(1-x) Tl-x, where x varies between 0 and 0.7, tends to decrease the glass transition and melting temperatures and to increase the DC conductivity in the amorphous phase. The activation energy for crystallisation of the amorphous solid phase is found to vary between 0.44 and 1.34 eV in a way which is similar to the compositional dependence of the electrical energy gap where there is a discontinuity at thallium concentrations of 2.25 x 10(21) atoms cm(-3) ( x = 0.25). Near that concentration some discontinuity is also found in the heat capacity results. This dependence has been linked with the substantial difference in the Tl bond configurations in the Tl-rich ( x > 0.25) and Tl-poor ( x <= 0.25) regions investigated.