It was shown that it required much less energy to form a Cu vacancy in this material, than to form cation vacancies in II-VI compounds. The defect formation energies varied considerably with the Fermi energy and with the chemical potential of the atomic species. Defect pairs, such as 2VCu-+InCu2+ and 2CuIn2-+InCu2+, had particularly low formation energies; which could even be exothermic under certain conditions. The above observations were used to explain the existence of unusual ordered compounds such as: CuIn5Se8, CuIn3Se5, Cu2In4Se7 and Cu3In5Se9, which involved the repeat of a single unit of 2VCu-+InCu2+ pairs for each 4, 5, 7 or 9 units, respectively, of CuInSe2. The very efficient p-type self-doping ability of CuInSe2 was attributed to the exceptionally low formation energy of shallow defect Cu vacancies. The electrically benign nature of the large defect population in CuInSe2 was explained in terms of the electronic passivation of InCu2+ by 2VCu-. Calculation indicated a new set of attributions of the defect transition energy levels which were observed in the band gap. The calculated level positions agreed quite well with the available experimental data.

S.B.Zhang, S.H.Wei, A.Zunger, E.Katayama-Yoshida: Physical Review B, 1998, 57[16], 9642-56