Thermal properties of a tetrahedrally bonded amorphous solid: CdGeAs2

We have measured the low-temperature thermal conductivity and specific heat of CdGeAs2 to investigate the influence of coordination number on the thermal properties of amorphous solids. CdGeAs2 is tetrahedrally bonded in the crystalline state and strong evidence exists that this local order is preserved in the amorphous state. The thermal conductivity of the amorphous material was measured from 0.1 to 300 K. It displays the same behavior as all other glasses: a T2 dependence below 1 K, a wide range of temperature over which the conductivity is approximately temperature independent, and a thermal conductivity at high temperatures that approaches the minimum thermal conductivity as described by Slack. The specific heats of c-CdGeAs2 and a-CdGeAs2 were measured from 0.1 to 50 K. Below 1 K, the amorphous material shows the excess specific heat that is characteristic of amorphous solids. Above 1 K, the specific heat of the amorphous material, when compared to the Debye model, closely resembles the specific heat of the crystal. We have also measured the thermal conductivity of a sputtered film of a-Ge from 30 to 300 K and compare our results to previous measurements of the thermal properties of a-Si and a-Ge. On the basis of our experimental findings, we conclude that the thermal properties of amorphous solids do not depend on the coordination number.