Structural characterization and electrical properties of quaternary CdGaInSe4 thin films

Stoichiometric bulk ingot material of the quaternary CdGaInSe4 was prepared by direct fusion of the constituent elements in vacuum-sealed silica tubes. Nearly stoichiometric films could be deposited by thermal evaporation of the ingot material in 10−3 Pa vacuum at a deposition rate 1.5 nm/s. Crystal structure investigation was carried out using X-ray diffractometry and transmission electron diffraction. Elemental composition was determined by means of energy-dispersive X-ray spectrometry. CdGaInSe4 possesses a tetragonal defective chalcopyrite structure (space group I¯4) with lattice parameters a=0.5665 nm and c=1.1221 nm. All the films exhibited n-type conduction and ohmic behaviour with metallic films of Au, Cd, In, Ag and Sb. However, in the case of Al a nonlinear behaviour occurs. Analysis of the temperature dependence of the dark conductivity in the range 130-470 K has revealed three operating conduction mechanisms; a variable range hopping conduction process dominating at low temperatures below 270 K, followed by a transport of the charge carriers across intercrystalline barriers and grain boundaries in the temperature range 270-353 K, and finally an extrinsic conduction above 353 K.