Effect of doping with transition and rare-earth metals on the electrical and optical properties of AgGaGe3Se8 single crystals

• Published in: Inorganic materials 2008-04, Vol.44 (4), p.361-365
• Main Authors: Davidyuk, G. E., Yurchenko, O. N., Parasyuk, O. V., Sachanyuk, V. P., Pankevich, V. Z., Shavarova, A. P.
• Format: Article
• Language: English
• Subjects: Chemistry; Chemistry and Materials Science; Industrial Chemistry/Chemical Engineering; Inorganic Chemistry; Materials Science
• ISSN: 0020-1685; 1608-3172
• DOI: 10.1134/S0020168508040067

We have studied the electrical, optical, and thermoelectric properties of AgGaGe 3 Se 8 single crystals grown by the Bridgman-Stockbarger method and doped with transition and rare-earth metals during growth. AgGaGe 3 Se 8 is an anisotropic p -type semiconductor with a band gap of ∼2.25 eV ( T ∼ 290 K), which decreases slightly, to ∼2.20 eV, on doping with Nd, Gd, and Er ( N ∼ 5 × 10 18 cm −3 ). The high concentration of stoichiometric silver vacancies ( N ∼ 1.8 × 10 20 cm −3 ) and random distribution of the Ga and Ge atoms over the cation sites give rise to static disorder, so that the structure of AgGaGe 3 Se 8 approaches that of disordered systems. This leads to the formation of electronic states in the band gap, intrinsic edge broadening, and, as a consequence, a drop in transmission. Depending on the concentration and nature of the dopant, doping of AgGaGe 3 Se 8 may lead to structural ordering and bleaching or may increase the destructive factor at high doping levels ( N > 10 18 cm −3 ). 60 Co gamma irradiation to a dose of 1.2–1.3 kGy reduces the absorption coefficient of AgGaGe 3 Se 8 crystals doped with high concentrations of Mn and Cu ( N > 5 × 10 18 cm −3 ). A model is proposed which explains the observed effects.