Research of thermodynamic properties of mid-infrared single crystal ZnGeP 2

Abstract Chalcopyrite ZnGeP 2 single crystal with sufficient size and quality was grown by modified vertical Bridgman method. The thermal expansion coefficients along a-axis and c-axis, α a and α c , were evaluated from the results of thermal dilatometer tests carried out in the range of 300–600 K. It is found that both α a and α c achieve positive values and α a is always larger than α c in the whole range indicating that the thermal expansion of the crystal exhibits anisotropic behavior. We selected the sample of c-axis and measured its thermal conductivity and molar specific heat. On this basis, the Gruneisen parameters of c-axis at different temperatures were calculated. Using these Gruneisen parameters, the lattice thermal conductivities have been deduced by one correction formula and we found that they are very close to the experimental results.