SPLTRAK Abstract Submission
Hybrid Functional Calculations for Antimony Doping in CdTe
Intuon Chatratin, Shagorika Mukherjee, Anderson Janotti
Department of Materials Science & Engineering, University of Delaware, Newark, DE, United States

CdTe-based  solar  cells  are  leading  thin-film  photovoltaic  technology,  with  efficiencies  over  22%, but still  much  lower  than  the  theoretical maximum of 29%. Further improvements will rely on increasing the open-circuit voltage Voc,  which,  in  turn,  depends  on  carrier  density  and  lifetime.  Early density functional calculations predicted a high ionization energy of 230 meV for the Sb acceptor in CdTe, and while more recent hybrid functional calculations give 150 meV, yet recent experimental data based on temperature Hall measurements of CdTe bulk single crystals indicate a much lower ionization energy of 103 meV. Using  hybrid  density  functional  calculations,  we  investigate Sb doping of CdTe, focusing on its limitation as shallow acceptor and the formation of compensating AX center. Paying special attention to supercell size  and effects of spin-orbit coupling, we predict an ionization energy of 116 meV in the dilute limit, much closer to recent experimental value of 103 meV. We also find that the Sb-related AX  center is not the major compensation center in Sb-doped CdTe and that further, analysis of the Hall data based our predicted ionization energy suggest that only a relatively low concentration of donors (~5% of the total Sb concentration) is necessary to explain experimental results. We speculate that Te vacancies are the unknown compensation centers.