Crystal growth and structural, electrical, and optical characterization of CuIn3Te5 and CuGa3Te5 ordered vacancy compounds

X-ray powder diffraction studies of ordered vacancy compounds ${\mathrm{CuIn}}_{\mathrm{3}}{\mathrm{Te}}_5$ and ${\mathrm{CuGa}}_{\mathrm{3}}{\mathrm{Te}}_5,$ prepared by the vertical Bridgman–Stockbarger technique, show that these materials exhibit a tetragonal chalcopyrite-related structure. The unit cell parameters a and c are, respectively, 6.1639(3) and 12.346(2) Å for ${\mathrm{CuIn}}_{\mathrm{3}}{\mathrm{Te}}_5,$ and 5.9321(8) and 11.825(4) Å for ${\mathrm{CuGa}}_{\mathrm{3}}{\mathrm{Te}}_5.$ From electrical resistivity characterization as a function of temperature a shallow acceptor level, with an activation energy lower than 30 meV, is found in both these compounds. Their direct energy gaps at room temperature are 1.013 and 1.092 eV for ${\mathrm{CuIn}}_{\mathrm{3}}{\mathrm{Te}}_5$ and ${\mathrm{CuGa}}_{\mathrm{3}}{\mathrm{Te}}_5,$ respectively.