Band offsets and point-defect charges of the aluminum and hafnium oxides in contact with the Cu(In,Ga)Sechalcopyrite.

Surface passivation of CuInSe(CIS) and related Cu(In,Ga)Se(CIGS) chalcopyrite materials by depositing selected dielectric layers has been a major research activity aiming to reduce interface recombination and increase the electrical efficiency of chalcopyrite-based thin-film solar cells. The present study reports calculations based on density-functional theory andthermodynamics that examine the origin of field-effect passivation from alumina and hafnia two wide-gap, predominantly ionic insulators that have exhibited promising passivation qualities in silicon-based microelectronics. The source of fixed charges within the bulk lattices of both oxides was studied by determining the thermodynamically most favorable charge states of their native defects within the admissible ranges of the metal and oxygen chemical potentials. An alignment of the electron bands based on the branch-point energies was performed in order to correctly place the defect charge-transition levels with respect to the band edges of the CIS and the CIGS materials. The trends and predictions of the sign of the fixed charges in either insulator were obtained as a function of temperature, oxygen partial pressure and Fermi-level position inside the band gaps of CIS and CIGS. The findings are discussed in connection with existing experimental studies that extracted the magnitude and polarity of the fixed charges of both alumina and hafnia by analyzing the electrical properties of the CIGS/insulator interfaces.