Electrical and optical properties of Cu2CdGeS4 single crystals

Cu2CdGeS4 single crystals are grown by chemical vapor transport and directional solidification, and their properties are studied. Independent of the growth technique, the crystals are p-type, with a 290-K Hall mobility of holes in the range 10-15 cm(2)/(V s). The room-temperature band gap of Cu2CdGeS4 evaluated from the position of its fundamental absorption edge is E-g approximate to 2.05 eV. The nature of the defects responsible for the near-IR absorption in Cu2CdGeS4 is assessed by analyzing the absorption spectra of stoichiometric crystals prepared by different techniques and melt-grown nonstoichiometric crystals. Some of the crystals studied have a thermoelectric power as high as 1800 mV/K. Based on the experimental data, a model is proposed for the electronic processes in Cu2CdGeS4, which accounts for the observed electrical and optical properties of this semiconductor.