Marquardt, J.; Gurieva, G.; Stephan-Scherb, C.; Schorr, S.: The Effect of Copper Vacancies on the Anion Position of Chalcopyrite Type CuGaS2. Physica Status Solidi A 216 (2019), p. 1800882/1-6
10.1002/pssa.201800882

Abstract:
The prediction of structural parameters and optoelectronic properties of compound semiconductors is very important. However, calculations often neglect chemical variability and structural defects. In chalcopyrite type semiconductors one of the major defects are copper vacancies (VCu). The four cation neighbors of the anion determine its position in the chalcopyrite type structure expressed by the Wyckoff position 8d (x, 1/4, 1/8). Intrinsic point defects like VCu and anti-sites may cause variations of the anion position in the middle of the cation tetrahedron, especially in the anion position parameter x. For stoichiometric chalcopyrite type compounds a formalism according to the principle of conservation of tetrahedral bonds (CTB) can be applied to calculate the anion position parameter, but it fails in the case of off-stoichiometric chalcopyrites. This case study of chalcopyrite type CuGaS2 and Mn-substituted GuGaS2 shows that the experimentally determined anion position parameter x deviate from values calculated by CTB approach. The systematic investigation of off-stoichiometric CuGaS2 and Mnsubstituted GuGaS2 demonstrates the effect of copper vacancies on the average radii of the cation sites (Wyckoff positions 4a and 4b) as well as on the anion position parameter x. By applying an elaborated CTB approach implementing copper vacancies an agreement between experimental and calculated anion position parameter x can be obtained.